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2013-08-31Merge branches 'doc.2013.08.19a', 'fixes.2013.08.20a', 'sysidle.2013.08.31a' ↵Paul E. McKenney
and 'torture.2013.08.20a' into HEAD doc.2013.08.19a: Documentation updates fixes.2013.08.20a: Miscellaneous fixes sysidle.2013.08.31a: Detect system-wide idle state. torture.2013.08.20a: rcutorture updates.
2013-08-31nohz_full: Force RCU's grace-period kthreads onto timekeeping CPUPaul E. McKenney
Because RCU's quiescent-state-forcing mechanism is used to drive the full-system-idle state machine, and because this mechanism is executed by RCU's grace-period kthreads, this commit forces these kthreads to run on the timekeeping CPU (tick_do_timer_cpu). To do otherwise would mean that the RCU grace-period kthreads would force the system into non-idle state every time they drove the state machine, which would be just a bit on the futile side. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-08-31nohz_full: Add full-system-idle state machinePaul E. McKenney
This commit adds the state machine that takes the per-CPU idle data as input and produces a full-system-idle indication as output. This state machine is driven out of RCU's quiescent-state-forcing mechanism, which invokes rcu_sysidle_check_cpu() to collect per-CPU idle state and then rcu_sysidle_report() to drive the state machine. The full-system-idle state is sampled using rcu_sys_is_idle(), which also drives the state machine if RCU is idle (and does so by forcing RCU to become non-idle). This function returns true if all but the timekeeping CPU (tick_do_timer_cpu) are idle and have been idle long enough to avoid memory contention on the full_sysidle_state state variable. The rcu_sysidle_force_exit() may be called externally to reset the state machine back into non-idle state. For large systems the state machine is driven out of RCU's force-quiescent-state logic, which provides good scalability at the price of millisecond-scale latencies on the transition to full-system-idle state. This is not so good for battery-powered systems, which are usually small enough that they don't need to care about scalability, but which do care deeply about energy efficiency. Small systems therefore drive the state machine directly out of the idle-entry code. The number of CPUs in a "small" system is defined by a new NO_HZ_FULL_SYSIDLE_SMALL Kconfig parameter, which defaults to 8. Note that this is a build-time definition. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> [ paulmck: Use true and false for boolean constants per Lai Jiangshan. ] Reviewed-by: Josh Triplett <josh@joshtriplett.org> [ paulmck: Simplify logic and provide better comments for memory barriers, based on review comments and questions by Lai Jiangshan. ]
2013-08-20rcu: Simplify _rcu_barrier() processingPaul E. McKenney
This commit drops an unneeded ACCESS_ONCE() and simplifies an "our work is done" check in _rcu_barrier(). This applies feedback from Linus (https://lkml.org/lkml/2013/7/26/777) that he gave to similar code in an unrelated patch. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org> [ paulmck: Fix comment to match code, reported by Lai Jiangshan. ]
2013-08-19nohz_full: Add full-system-idle arguments to APIPaul E. McKenney
This commit adds an isidle and jiffies argument to force_qs_rnp(), dyntick_save_progress_counter(), and rcu_implicit_dynticks_qs() to enable RCU's force-quiescent-state process to check for full-system idle. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> [ paulmck: Use true and false for boolean constants per Lai Jiangshan. ] Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-08-19nohz_full: Add per-CPU idle-state trackingPaul E. McKenney
This commit adds the code that updates the rcu_dyntick structure's new fields to track the per-CPU idle state based on interrupts and transitions into and out of the idle loop (NMIs are ignored because NMI handlers cannot cleanly read out the time anyway). This code is similar to the code that maintains RCU's idea of per-CPU idleness, but differs in that RCU treats CPUs running in user mode as idle, where this new code does not. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Steven Rostedt <rostedt@goodmis.org> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-08-19nohz_full: Add rcu_dyntick data for scalable detection of all-idle statePaul E. McKenney
This commit adds fields to the rcu_dyntick structure that are used to detect idle CPUs. These new fields differ from the existing ones in that the existing ones consider a CPU executing in user mode to be idle, where the new ones consider CPUs executing in user mode to be busy. The handling of these new fields is otherwise quite similar to that for the exiting fields. This commit also adds the initialization required for these fields. So, why is usermode execution treated differently, with RCU considering it a quiescent state equivalent to idle, while in contrast the new full-system idle state detection considers usermode execution to be non-idle? It turns out that although one of RCU's quiescent states is usermode execution, it is not a full-system idle state. This is because the purpose of the full-system idle state is not RCU, but rather determining when accurate timekeeping can safely be disabled. Whenever accurate timekeeping is required in a CONFIG_NO_HZ_FULL kernel, at least one CPU must keep the scheduling-clock tick going. If even one CPU is executing in user mode, accurate timekeeping is requires, particularly for architectures where gettimeofday() and friends do not enter the kernel. Only when all CPUs are really and truly idle can accurate timekeeping be disabled, allowing all CPUs to turn off the scheduling clock interrupt, thus greatly improving energy efficiency. This naturally raises the question "Why is this code in RCU rather than in timekeeping?", and the answer is that RCU has the data and infrastructure to efficiently make this determination. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Steven Rostedt <rostedt@goodmis.org> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-08-19rcu: Eliminate unused APIs intended for adaptive ticksPaul E. McKenney
The rcu_user_enter_after_irq() and rcu_user_exit_after_irq() functions were intended for use by adaptive ticks, but changes in implementation have rendered them unnecessary. This commit therefore removes them. Reported-by: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-08-19rcu: Avoid redundant grace-period kthread wakeupsPaul E. McKenney
When setting up an in-the-future "advanced" grace period, the code needs to wake up the relevant grace-period kthread, which it currently does unconditionally. However, this results in needless wakeups in the case where the advanced grace period is being set up by the grace-period kthread itself, which is a non-uncommon situation. This commit therefore checks to see if the running thread is the grace-period kthread, and avoids doing the irq_work_queue()-mediated wakeup in that case. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-08-19rcu: Make call_rcu() leak callbacks for debug-object errorsPaul E. McKenney
If someone does a duplicate call_rcu(), the worst thing the second call_rcu() could do would be to actually queue the callback the second time because doing so corrupts whatever list the callback was already queued on. This commit therefore makes __call_rcu() check the new return value from debug-objects and leak the callback upon error. This commit also substitutes rcu_leak_callback() for whatever callback function was previously in place in order to avoid freeing the callback out from under any readers that might still be referencing it. These changes increase the probability that the debug-objects error messages will actually make it somewhere visible. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Sedat Dilek <sedat.dilek@gmail.com> Cc: Davidlohr Bueso <davidlohr.bueso@hp.com> Cc: Rik van Riel <riel@surriel.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Linus Torvalds <torvalds@linux-foundation.org> Tested-by: Sedat Dilek <sedat.dilek@gmail.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-08-19rcu: Expedite grace periods during suspend/resumeBorislav Petkov
CONFIG_RCU_FAST_NO_HZ can increase grace-period durations by up to a factor of four, which can result in long suspend and resume times. Thus, this commit temporarily switches to expedited grace periods when suspending the box and return to normal settings when resuming. Similar logic is applied to hibernation. Because expedited grace periods are of dubious benefit on very large systems, so this commit restricts their automated use during suspend and resume to systems of 256 or fewer CPUs. (Some day a number of Linux-kernel facilities, including RCU's expedited grace periods, will be more scalable, but I need to see bug reports first.) [ paulmck: This also papers over an audio/irq bug, but hopefully that will be fixed soon. ] Signed-off-by: Borislav Petkov <bp@suse.de> Signed-off-by: Bjørn Mork <bjorn@mork.no> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-07-29rcu: Have the RCU tracepoints use the tracepoint_string infrastructureSteven Rostedt (Red Hat)
Currently, RCU tracepoints save only a pointer to strings in the ring buffer. When displayed via the /sys/kernel/debug/tracing/trace file they are referenced like the printf "%s" that looks at the address in the ring buffer and prints out the string it points too. This requires that the strings are constant and persistent in the kernel. The problem with this is for tools like trace-cmd and perf that read the binary data from the buffers but have no access to the kernel memory to find out what string is represented by the address in the buffer. By using the tracepoint_string infrastructure, the RCU tracepoint strings can be exported such that userspace tools can map the addresses to the strings. # cat /sys/kernel/debug/tracing/printk_formats 0xffffffff81a4a0e8 : "rcu_preempt" 0xffffffff81a4a0f4 : "rcu_bh" 0xffffffff81a4a100 : "rcu_sched" 0xffffffff818437a0 : "cpuqs" 0xffffffff818437a6 : "rcu_sched" 0xffffffff818437a0 : "cpuqs" 0xffffffff818437b0 : "rcu_bh" 0xffffffff818437b7 : "Start context switch" 0xffffffff818437cc : "End context switch" 0xffffffff818437a0 : "cpuqs" [...] Now userspaces tools can display: rcu_utilization: Start context switch rcu_dyntick: Start 1 0 rcu_utilization: End context switch rcu_batch_start: rcu_preempt CBs=0/5 bl=10 rcu_dyntick: End 0 140000000000000 rcu_invoke_callback: rcu_preempt rhp=0xffff880071c0d600 func=proc_i_callback rcu_invoke_callback: rcu_preempt rhp=0xffff880077b5b230 func=__d_free rcu_dyntick: Start 140000000000000 0 rcu_invoke_callback: rcu_preempt rhp=0xffff880077563980 func=file_free_rcu rcu_batch_end: rcu_preempt CBs-invoked=3 idle=>c<>c<>c<>c< rcu_utilization: End RCU core rcu_grace_period: rcu_preempt 9741 start rcu_dyntick: Start 1 0 rcu_dyntick: End 0 140000000000000 rcu_dyntick: Start 140000000000000 0 Instead of: rcu_utilization: ffffffff81843110 rcu_future_grace_period: ffffffff81842f1d 9939 9939 9940 0 0 3 ffffffff81842f32 rcu_batch_start: ffffffff81842f1d CBs=0/4 bl=10 rcu_future_grace_period: ffffffff81842f1d 9939 9939 9940 0 0 3 ffffffff81842f3c rcu_grace_period: ffffffff81842f1d 9939 ffffffff81842f80 rcu_invoke_callback: ffffffff81842f1d rhp=0xffff88007888aac0 func=file_free_rcu rcu_grace_period: ffffffff81842f1d 9939 ffffffff81842f95 rcu_invoke_callback: ffffffff81842f1d rhp=0xffff88006aeb4600 func=proc_i_callback rcu_future_grace_period: ffffffff81842f1d 9939 9939 9940 0 0 3 ffffffff81842f32 rcu_future_grace_period: ffffffff81842f1d 9939 9939 9940 0 0 3 ffffffff81842f3c rcu_invoke_callback: ffffffff81842f1d rhp=0xffff880071cb9fc0 func=__d_free rcu_grace_period: ffffffff81842f1d 9939 ffffffff81842f80 rcu_invoke_callback: ffffffff81842f1d rhp=0xffff88007888ae80 func=file_free_rcu rcu_batch_end: ffffffff81842f1d CBs-invoked=4 idle=>c<>c<>c<>c< rcu_utilization: ffffffff8184311f Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2013-07-29rcu: Simplify RCU_STATE_INITIALIZER() macroSteven Rostedt (Red Hat)
The RCU_STATE_INITIALIZER() macro is used only in the rcutree.c file as well as the rcutree_plugin.h file. It is passed as a rvalue to a variable of a similar name. A per_cpu variable is also created with a similar name as well. The uses of RCU_STATE_INITIALIZER() can be simplified to remove some of the duplicate code that is done. Currently the three users of this macro has this format: struct rcu_state rcu_sched_state = RCU_STATE_INITIALIZER(rcu_sched, call_rcu_sched); DEFINE_PER_CPU(struct rcu_data, rcu_sched_data); Notice that "rcu_sched" is called three times. This is the same with the other two users. This can be condensed to just: RCU_STATE_INITIALIZER(rcu_sched, call_rcu_sched); by moving the rest into the macro itself. This also opens the door to allow the RCU tracepoint strings and their addresses to be exported so that userspace tracing tools can translate the contents of the pointers of the RCU tracepoints. The change will allow for helper code to be placed in the RCU_STATE_INITIALIZER() macro to export the name that is used. Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2013-07-29rcu: Add const annotation to char * for RCU tracepoints and functionsSteven Rostedt (Red Hat)
All the RCU tracepoints and functions that reference char pointers do so with just 'char *' even though they do not modify the contents of the string itself. This will cause warnings if a const char * is used in one of these functions. The RCU tracepoints store the pointer to the string to refer back to them when the trace output is displayed. As this can be minutes, hours or even days later, those strings had better be constant. This change also opens the door to allow the RCU tracepoint strings and their addresses to be exported so that userspace tracing tools can translate the contents of the pointers of the RCU tracepoints. Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2013-07-14rcu: delete __cpuinit usage from all rcu filesPaul Gortmaker
The __cpuinit type of throwaway sections might have made sense some time ago when RAM was more constrained, but now the savings do not offset the cost and complications. For example, the fix in commit 5e427ec2d0 ("x86: Fix bit corruption at CPU resume time") is a good example of the nasty type of bugs that can be created with improper use of the various __init prefixes. After a discussion on LKML[1] it was decided that cpuinit should go the way of devinit and be phased out. Once all the users are gone, we can then finally remove the macros themselves from linux/init.h. This removes all the drivers/rcu uses of the __cpuinit macros from all C files. [1] https://lkml.org/lkml/2013/5/20/589 Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Cc: Josh Triplett <josh@freedesktop.org> Cc: Dipankar Sarma <dipankar@in.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org> Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
2013-07-03drivers: avoid parsing names as kthread_run() format stringsKees Cook
Calling kthread_run with a single name parameter causes it to be handled as a format string. Many callers are passing potentially dynamic string content, so use "%s" in those cases to avoid any potential accidents. Signed-off-by: Kees Cook <keescook@chromium.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2013-06-10Merge branches 'cbnum.2013.06.10a', 'doc.2013.06.10a', 'fixes.2013.06.10a', ↵Paul E. McKenney
'srcu.2013.06.10a' and 'tiny.2013.06.10a' into HEAD cbnum.2013.06.10a: Apply simplifications stemming from the new callback numbering. doc.2013.06.10a: Documentation updates. fixes.2013.06.10a: Miscellaneous fixes. srcu.2013.06.10a: Updates to SRCU. tiny.2013.06.10a: Eliminate TINY_PREEMPT_RCU.
2013-06-10rcu: Drive quiescent-state-forcing delay from HZPaul E. McKenney
Systems with HZ=100 can have slow bootup times due to the default three-jiffy delays between quiescent-state forcing attempts. This commit therefore auto-tunes the RCU_JIFFIES_TILL_FORCE_QS value based on the value of HZ. However, this would break very large systems that require more time between quiescent-state forcing attempts. This commit therefore also ups the default delay by one jiffy for each 256 CPUs that might be on the system (based off of nr_cpu_ids at runtime, -not- NR_CPUS at build time). Updated to collapse #ifdefs for RCU_JIFFIES_TILL_FORCE_QS into a step-function definition as suggested by Josh Triplett. Reported-by: Paul Mackerras <paulus@au1.ibm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2013-06-10rcu: Move redundant call to note_gp_changes() into called functionPaul E. McKenney
The __rcu_process_callbacks() invokes note_gp_changes() immediately before invoking rcu_check_quiescent_state(), which conditionally invokes that same function. This commit therefore eliminates the call to note_gp_changes() in __rcu_process_callbacks() in favor of making unconditional to call from rcu_check_quiescent_state() to note_gp_changes(). Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-06-10rcu: Inline trivial wrapper function rcu_start_gp_per_cpu()Paul E. McKenney
Given the changes that introduce note_gp_change(), rcu_start_gp_per_cpu() is now a trivial wrapper function with only one caller. This commit therefore inlines it into its sole call site. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-06-10rcu: Eliminate check_for_new_grace_period() wrapper functionPaul E. McKenney
One of the calls to check_for_new_grace_period() is now redundant due to an immediately preceding call to note_gp_changes(). Eliminating this redundant call leaves a single caller, which is simpler if inlined. This commit therefore eliminates the redundant call and inlines the body of check_for_new_grace_period() into the single remaining call site. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-06-10rcu: Merge __rcu_process_gp_end() into __note_gp_changes()Paul E. McKenney
This commit eliminates some duplicated code by merging __rcu_process_gp_end() into __note_gp_changes(). Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-06-10rcu: Switch callers from rcu_process_gp_end() to note_gp_changes()Paul E. McKenney
Because note_gp_changes() now incorporates rcu_process_gp_end() function, this commit switches to the former and eliminates the latter. In addition, this commit changes external calls from __rcu_process_gp_end() to __note_gp_changes(). Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-06-10rcu: Rename note_new_gpnum() to note_gp_changes()Paul E. McKenney
Because note_new_gpnum() now also checks for the ends of old grace periods, this commit changes its name to note_gp_changes(). Later commits will merge rcu_process_gp_end() into note_gp_changes(). Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-06-10rcu: Make __note_new_gpnum() check for ends of prior grace periodsPaul E. McKenney
The current implementation can detect the beginning of a new grace period before noting the end of a previous grace period. Although the current implementation correctly handles this sort of nonsense, it would be good to reduce RCU's state space by making such nonsense unnecessary, which is now possible thanks to the fact that RCU's callback groups are now numbered. This commit therefore makes __note_new_gpnum() invoke __rcu_process_gp_end() in order to note the ends of prior grace periods before noting the beginnings of new grace periods. Of course, this now means that note_new_gpnum() notes both the beginnings and ends of grace periods, and could therefore be used in place of rcu_process_gp_end(). But that is a job for later commits. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-06-10rcu: Move code to apply callback-numbering simplificationsPaul E. McKenney
The addition of callback numbering allows combining the detection of the ends of old grace periods and the beginnings of new grace periods. This commit moves code to set the stage for this combining. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-06-10rcu: Convert rcutree.c printk callsPaul E. McKenney
This commit converts printk() calls to the corresponding pr_*() calls. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-06-10rcu: Fix deadlock with CPU hotplug, RCU GP init, and timer migrationPaul E. McKenney
In Steven Rostedt's words: > I've been debugging the last couple of days why my tests have been > locking up. One of my tracing tests, runs all available tracers. The > lockup always happened with the mmiotrace, which is used to trace > interactions between priority drivers and the kernel. But to do this > easily, when the tracer gets registered, it disables all but the boot > CPUs. The lockup always happened after it got done disabling the CPUs. > > Then I decided to try this: > > while :; do > for i in 1 2 3; do > echo 0 > /sys/devices/system/cpu/cpu$i/online > done > for i in 1 2 3; do > echo 1 > /sys/devices/system/cpu/cpu$i/online > done > done > > Well, sure enough, that locked up too, with the same users. Doing a > sysrq-w (showing all blocked tasks): > > [ 2991.344562] task PC stack pid father > [ 2991.344562] rcu_preempt D ffff88007986fdf8 0 10 2 0x00000000 > [ 2991.344562] ffff88007986fc98 0000000000000002 ffff88007986fc48 0000000000000908 > [ 2991.344562] ffff88007986c280 ffff88007986ffd8 ffff88007986ffd8 00000000001d3c80 > [ 2991.344562] ffff880079248a40 ffff88007986c280 0000000000000000 00000000fffd4295 > [ 2991.344562] Call Trace: > [ 2991.344562] [<ffffffff815437ba>] schedule+0x64/0x66 > [ 2991.344562] [<ffffffff81541750>] schedule_timeout+0xbc/0xf9 > [ 2991.344562] [<ffffffff8154bec0>] ? ftrace_call+0x5/0x2f > [ 2991.344562] [<ffffffff81049513>] ? cascade+0xa8/0xa8 > [ 2991.344562] [<ffffffff815417ab>] schedule_timeout_uninterruptible+0x1e/0x20 > [ 2991.344562] [<ffffffff810c980c>] rcu_gp_kthread+0x502/0x94b > [ 2991.344562] [<ffffffff81062791>] ? __init_waitqueue_head+0x50/0x50 > [ 2991.344562] [<ffffffff810c930a>] ? rcu_gp_fqs+0x64/0x64 > [ 2991.344562] [<ffffffff81061cdb>] kthread+0xb1/0xb9 > [ 2991.344562] [<ffffffff81091e31>] ? lock_release_holdtime.part.23+0x4e/0x55 > [ 2991.344562] [<ffffffff81061c2a>] ? __init_kthread_worker+0x58/0x58 > [ 2991.344562] [<ffffffff8154c1dc>] ret_from_fork+0x7c/0xb0 > [ 2991.344562] [<ffffffff81061c2a>] ? __init_kthread_worker+0x58/0x58 > [ 2991.344562] kworker/0:1 D ffffffff81a30680 0 47 2 0x00000000 > [ 2991.344562] Workqueue: events cpuset_hotplug_workfn > [ 2991.344562] ffff880078dbbb58 0000000000000002 0000000000000006 00000000000000d8 > [ 2991.344562] ffff880078db8100 ffff880078dbbfd8 ffff880078dbbfd8 00000000001d3c80 > [ 2991.344562] ffff8800779ca5c0 ffff880078db8100 ffffffff81541fcf 0000000000000000 > [ 2991.344562] Call Trace: > [ 2991.344562] [<ffffffff81541fcf>] ? __mutex_lock_common+0x3d4/0x609 > [ 2991.344562] [<ffffffff815437ba>] schedule+0x64/0x66 > [ 2991.344562] [<ffffffff81543a39>] schedule_preempt_disabled+0x18/0x24 > [ 2991.344562] [<ffffffff81541fcf>] __mutex_lock_common+0x3d4/0x609 > [ 2991.344562] [<ffffffff8103d11b>] ? get_online_cpus+0x3c/0x50 > [ 2991.344562] [<ffffffff8103d11b>] ? get_online_cpus+0x3c/0x50 > [ 2991.344562] [<ffffffff815422ff>] mutex_lock_nested+0x3b/0x40 > [ 2991.344562] [<ffffffff8103d11b>] get_online_cpus+0x3c/0x50 > [ 2991.344562] [<ffffffff810af7e6>] rebuild_sched_domains_locked+0x6e/0x3a8 > [ 2991.344562] [<ffffffff810b0ec6>] rebuild_sched_domains+0x1c/0x2a > [ 2991.344562] [<ffffffff810b109b>] cpuset_hotplug_workfn+0x1c7/0x1d3 > [ 2991.344562] [<ffffffff810b0ed9>] ? cpuset_hotplug_workfn+0x5/0x1d3 > [ 2991.344562] [<ffffffff81058e07>] process_one_work+0x2d4/0x4d1 > [ 2991.344562] [<ffffffff81058d3a>] ? process_one_work+0x207/0x4d1 > [ 2991.344562] [<ffffffff8105964c>] worker_thread+0x2e7/0x3b5 > [ 2991.344562] [<ffffffff81059365>] ? rescuer_thread+0x332/0x332 > [ 2991.344562] [<ffffffff81061cdb>] kthread+0xb1/0xb9 > [ 2991.344562] [<ffffffff81061c2a>] ? __init_kthread_worker+0x58/0x58 > [ 2991.344562] [<ffffffff8154c1dc>] ret_from_fork+0x7c/0xb0 > [ 2991.344562] [<ffffffff81061c2a>] ? __init_kthread_worker+0x58/0x58 > [ 2991.344562] bash D ffffffff81a4aa80 0 2618 2612 0x10000000 > [ 2991.344562] ffff8800379abb58 0000000000000002 0000000000000006 0000000000000c2c > [ 2991.344562] ffff880077fea140 ffff8800379abfd8 ffff8800379abfd8 00000000001d3c80 > [ 2991.344562] ffff8800779ca5c0 ffff880077fea140 ffffffff81541fcf 0000000000000000 > [ 2991.344562] Call Trace: > [ 2991.344562] [<ffffffff81541fcf>] ? __mutex_lock_common+0x3d4/0x609 > [ 2991.344562] [<ffffffff815437ba>] schedule+0x64/0x66 > [ 2991.344562] [<ffffffff81543a39>] schedule_preempt_disabled+0x18/0x24 > [ 2991.344562] [<ffffffff81541fcf>] __mutex_lock_common+0x3d4/0x609 > [ 2991.344562] [<ffffffff81530078>] ? rcu_cpu_notify+0x2f5/0x86e > [ 2991.344562] [<ffffffff81530078>] ? rcu_cpu_notify+0x2f5/0x86e > [ 2991.344562] [<ffffffff815422ff>] mutex_lock_nested+0x3b/0x40 > [ 2991.344562] [<ffffffff81530078>] rcu_cpu_notify+0x2f5/0x86e > [ 2991.344562] [<ffffffff81091c99>] ? __lock_is_held+0x32/0x53 > [ 2991.344562] [<ffffffff81548912>] notifier_call_chain+0x6b/0x98 > [ 2991.344562] [<ffffffff810671fd>] __raw_notifier_call_chain+0xe/0x10 > [ 2991.344562] [<ffffffff8103cf64>] __cpu_notify+0x20/0x32 > [ 2991.344562] [<ffffffff8103cf8d>] cpu_notify_nofail+0x17/0x36 > [ 2991.344562] [<ffffffff815225de>] _cpu_down+0x154/0x259 > [ 2991.344562] [<ffffffff81522710>] cpu_down+0x2d/0x3a > [ 2991.344562] [<ffffffff81526351>] store_online+0x4e/0xe7 > [ 2991.344562] [<ffffffff8134d764>] dev_attr_store+0x20/0x22 > [ 2991.344562] [<ffffffff811b3c5f>] sysfs_write_file+0x108/0x144 > [ 2991.344562] [<ffffffff8114c5ef>] vfs_write+0xfd/0x158 > [ 2991.344562] [<ffffffff8114c928>] SyS_write+0x5c/0x83 > [ 2991.344562] [<ffffffff8154c494>] tracesys+0xdd/0xe2 > > As well as held locks: > > [ 3034.728033] Showing all locks held in the system: > [ 3034.728033] 1 lock held by rcu_preempt/10: > [ 3034.728033] #0: (rcu_preempt_state.onoff_mutex){+.+...}, at: [<ffffffff810c9471>] rcu_gp_kthread+0x167/0x94b > [ 3034.728033] 4 locks held by kworker/0:1/47: > [ 3034.728033] #0: (events){.+.+.+}, at: [<ffffffff81058d3a>] process_one_work+0x207/0x4d1 > [ 3034.728033] #1: (cpuset_hotplug_work){+.+.+.}, at: [<ffffffff81058d3a>] process_one_work+0x207/0x4d1 > [ 3034.728033] #2: (cpuset_mutex){+.+.+.}, at: [<ffffffff810b0ec1>] rebuild_sched_domains+0x17/0x2a > [ 3034.728033] #3: (cpu_hotplug.lock){+.+.+.}, at: [<ffffffff8103d11b>] get_online_cpus+0x3c/0x50 > [ 3034.728033] 1 lock held by mingetty/2563: > [ 3034.728033] #0: (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8131e28a>] n_tty_read+0x252/0x7e8 > [ 3034.728033] 1 lock held by mingetty/2565: > [ 3034.728033] #0: (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8131e28a>] n_tty_read+0x252/0x7e8 > [ 3034.728033] 1 lock held by mingetty/2569: > [ 3034.728033] #0: (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8131e28a>] n_tty_read+0x252/0x7e8 > [ 3034.728033] 1 lock held by mingetty/2572: > [ 3034.728033] #0: (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8131e28a>] n_tty_read+0x252/0x7e8 > [ 3034.728033] 1 lock held by mingetty/2575: > [ 3034.728033] #0: (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8131e28a>] n_tty_read+0x252/0x7e8 > [ 3034.728033] 7 locks held by bash/2618: > [ 3034.728033] #0: (sb_writers#5){.+.+.+}, at: [<ffffffff8114bc3f>] file_start_write+0x2a/0x2c > [ 3034.728033] #1: (&buffer->mutex#2){+.+.+.}, at: [<ffffffff811b3b93>] sysfs_write_file+0x3c/0x144 > [ 3034.728033] #2: (s_active#54){.+.+.+}, at: [<ffffffff811b3c3e>] sysfs_write_file+0xe7/0x144 > [ 3034.728033] #3: (x86_cpu_hotplug_driver_mutex){+.+.+.}, at: [<ffffffff810217c2>] cpu_hotplug_driver_lock+0x17/0x19 > [ 3034.728033] #4: (cpu_add_remove_lock){+.+.+.}, at: [<ffffffff8103d196>] cpu_maps_update_begin+0x17/0x19 > [ 3034.728033] #5: (cpu_hotplug.lock){+.+.+.}, at: [<ffffffff8103cfd8>] cpu_hotplug_begin+0x2c/0x6d > [ 3034.728033] #6: (rcu_preempt_state.onoff_mutex){+.+...}, at: [<ffffffff81530078>] rcu_cpu_notify+0x2f5/0x86e > [ 3034.728033] 1 lock held by bash/2980: > [ 3034.728033] #0: (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8131e28a>] n_tty_read+0x252/0x7e8 > > Things looked a little weird. Also, this is a deadlock that lockdep did > not catch. But what we have here does not look like a circular lock > issue: > > Bash is blocked in rcu_cpu_notify(): > > 1961 /* Exclude any attempts to start a new grace period. */ > 1962 mutex_lock(&rsp->onoff_mutex); > > > kworker is blocked in get_online_cpus(), which makes sense as we are > currently taking down a CPU. > > But rcu_preempt is not blocked on anything. It is simply sleeping in > rcu_gp_kthread (really rcu_gp_init) here: > > 1453 #ifdef CONFIG_PROVE_RCU_DELAY > 1454 if ((prandom_u32() % (rcu_num_nodes * 8)) == 0 && > 1455 system_state == SYSTEM_RUNNING) > 1456 schedule_timeout_uninterruptible(2); > 1457 #endif /* #ifdef CONFIG_PROVE_RCU_DELAY */ > > And it does this while holding the onoff_mutex that bash is waiting for. > > Doing a function trace, it showed me where it happened: > > [ 125.940066] rcu_pree-10 3.... 28384115273: schedule_timeout_uninterruptible <-rcu_gp_kthread > [...] > [ 125.940066] rcu_pree-10 3d..3 28384202439: sched_switch: prev_comm=rcu_preempt prev_pid=10 prev_prio=120 prev_state=D ==> next_comm=watchdog/3 next_pid=38 next_prio=120 > > The watchdog ran, and then: > > [ 125.940066] watchdog-38 3d..3 28384692863: sched_switch: prev_comm=watchdog/3 prev_pid=38 prev_prio=120 prev_state=P ==> next_comm=modprobe next_pid=2848 next_prio=118 > > Not sure what modprobe was doing, but shortly after that: > > [ 125.940066] modprobe-2848 3d..3 28385041749: sched_switch: prev_comm=modprobe prev_pid=2848 prev_prio=118 prev_state=R+ ==> next_comm=migration/3 next_pid=40 next_prio=0 > > Where the migration thread took down the CPU: > > [ 125.940066] migratio-40 3d..3 28389148276: sched_switch: prev_comm=migration/3 prev_pid=40 prev_prio=0 prev_state=P ==> next_comm=swapper/3 next_pid=0 next_prio=120 > > which finally did: > > [ 125.940066] <idle>-0 3...1 28389282142: arch_cpu_idle_dead <-cpu_startup_entry > [ 125.940066] <idle>-0 3...1 28389282548: native_play_dead <-arch_cpu_idle_dead > [ 125.940066] <idle>-0 3...1 28389282924: play_dead_common <-native_play_dead > [ 125.940066] <idle>-0 3...1 28389283468: idle_task_exit <-play_dead_common > [ 125.940066] <idle>-0 3...1 28389284644: amd_e400_remove_cpu <-play_dead_common > > > CPU 3 is now offline, the rcu_preempt thread that ran on CPU 3 is still > doing a schedule_timeout_uninterruptible() and it registered it's > timeout to the timer base for CPU 3. You would think that it would get > migrated right? The issue here is that the timer migration happens at > the CPU notifier for CPU_DEAD. The problem is that the rcu notifier for > CPU_DOWN is blocked waiting for the onoff_mutex to be released, which is > held by the thread that just put itself into a uninterruptible sleep, > that wont wake up until the CPU_DEAD notifier of the timer > infrastructure is called, which wont happen until the rcu notifier > finishes. Here's our deadlock! This commit breaks this deadlock cycle by substituting a shorter udelay() for the previous schedule_timeout_uninterruptible(), while at the same time increasing the probability of the delay. This maintains the intensity of the testing. Reported-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Tested-by: Steven Rostedt <rostedt@goodmis.org>
2013-06-10rcu: Don't call wakeup() with rcu_node structure ->lock heldSteven Rostedt
This commit fixes a lockdep-detected deadlock by moving a wake_up() call out from a rnp->lock critical section. Please see below for the long version of this story. On Tue, 2013-05-28 at 16:13 -0400, Dave Jones wrote: > [12572.705832] ====================================================== > [12572.750317] [ INFO: possible circular locking dependency detected ] > [12572.796978] 3.10.0-rc3+ #39 Not tainted > [12572.833381] ------------------------------------------------------- > [12572.862233] trinity-child17/31341 is trying to acquire lock: > [12572.870390] (rcu_node_0){..-.-.}, at: [<ffffffff811054ff>] rcu_read_unlock_special+0x9f/0x4c0 > [12572.878859] > but task is already holding lock: > [12572.894894] (&ctx->lock){-.-...}, at: [<ffffffff811390ed>] perf_lock_task_context+0x7d/0x2d0 > [12572.903381] > which lock already depends on the new lock. > > [12572.927541] > the existing dependency chain (in reverse order) is: > [12572.943736] > -> #4 (&ctx->lock){-.-...}: > [12572.960032] [<ffffffff810b9851>] lock_acquire+0x91/0x1f0 > [12572.968337] [<ffffffff816ebc90>] _raw_spin_lock+0x40/0x80 > [12572.976633] [<ffffffff8113c987>] __perf_event_task_sched_out+0x2e7/0x5e0 > [12572.984969] [<ffffffff81088953>] perf_event_task_sched_out+0x93/0xa0 > [12572.993326] [<ffffffff816ea0bf>] __schedule+0x2cf/0x9c0 > [12573.001652] [<ffffffff816eacfe>] schedule_user+0x2e/0x70 > [12573.009998] [<ffffffff816ecd64>] retint_careful+0x12/0x2e > [12573.018321] > -> #3 (&rq->lock){-.-.-.}: > [12573.034628] [<ffffffff810b9851>] lock_acquire+0x91/0x1f0 > [12573.042930] [<ffffffff816ebc90>] _raw_spin_lock+0x40/0x80 > [12573.051248] [<ffffffff8108e6a7>] wake_up_new_task+0xb7/0x260 > [12573.059579] [<ffffffff810492f5>] do_fork+0x105/0x470 > [12573.067880] [<ffffffff81049686>] kernel_thread+0x26/0x30 > [12573.076202] [<ffffffff816cee63>] rest_init+0x23/0x140 > [12573.084508] [<ffffffff81ed8e1f>] start_kernel+0x3f1/0x3fe > [12573.092852] [<ffffffff81ed856f>] x86_64_start_reservations+0x2a/0x2c > [12573.101233] [<ffffffff81ed863d>] x86_64_start_kernel+0xcc/0xcf > [12573.109528] > -> #2 (&p->pi_lock){-.-.-.}: > [12573.125675] [<ffffffff810b9851>] lock_acquire+0x91/0x1f0 > [12573.133829] [<ffffffff816ebe9b>] _raw_spin_lock_irqsave+0x4b/0x90 > [12573.141964] [<ffffffff8108e881>] try_to_wake_up+0x31/0x320 > [12573.150065] [<ffffffff8108ebe2>] default_wake_function+0x12/0x20 > [12573.158151] [<ffffffff8107bbf8>] autoremove_wake_function+0x18/0x40 > [12573.166195] [<ffffffff81085398>] __wake_up_common+0x58/0x90 > [12573.174215] [<ffffffff81086909>] __wake_up+0x39/0x50 > [12573.182146] [<ffffffff810fc3da>] rcu_start_gp_advanced.isra.11+0x4a/0x50 > [12573.190119] [<ffffffff810fdb09>] rcu_start_future_gp+0x1c9/0x1f0 > [12573.198023] [<ffffffff810fe2c4>] rcu_nocb_kthread+0x114/0x930 > [12573.205860] [<ffffffff8107a91d>] kthread+0xed/0x100 > [12573.213656] [<ffffffff816f4b1c>] ret_from_fork+0x7c/0xb0 > [12573.221379] > -> #1 (&rsp->gp_wq){..-.-.}: > [12573.236329] [<ffffffff810b9851>] lock_acquire+0x91/0x1f0 > [12573.243783] [<ffffffff816ebe9b>] _raw_spin_lock_irqsave+0x4b/0x90 > [12573.251178] [<ffffffff810868f3>] __wake_up+0x23/0x50 > [12573.258505] [<ffffffff810fc3da>] rcu_start_gp_advanced.isra.11+0x4a/0x50 > [12573.265891] [<ffffffff810fdb09>] rcu_start_future_gp+0x1c9/0x1f0 > [12573.273248] [<ffffffff810fe2c4>] rcu_nocb_kthread+0x114/0x930 > [12573.280564] [<ffffffff8107a91d>] kthread+0xed/0x100 > [12573.287807] [<ffffffff816f4b1c>] ret_from_fork+0x7c/0xb0 Notice the above call chain. rcu_start_future_gp() is called with the rnp->lock held. Then it calls rcu_start_gp_advance, which does a wakeup. You can't do wakeups while holding the rnp->lock, as that would mean that you could not do a rcu_read_unlock() while holding the rq lock, or any lock that was taken while holding the rq lock. This is because... (See below). > [12573.295067] > -> #0 (rcu_node_0){..-.-.}: > [12573.309293] [<ffffffff810b8d36>] __lock_acquire+0x1786/0x1af0 > [12573.316568] [<ffffffff810b9851>] lock_acquire+0x91/0x1f0 > [12573.323825] [<ffffffff816ebc90>] _raw_spin_lock+0x40/0x80 > [12573.331081] [<ffffffff811054ff>] rcu_read_unlock_special+0x9f/0x4c0 > [12573.338377] [<ffffffff810760a6>] __rcu_read_unlock+0x96/0xa0 > [12573.345648] [<ffffffff811391b3>] perf_lock_task_context+0x143/0x2d0 > [12573.352942] [<ffffffff8113938e>] find_get_context+0x4e/0x1f0 > [12573.360211] [<ffffffff811403f4>] SYSC_perf_event_open+0x514/0xbd0 > [12573.367514] [<ffffffff81140e49>] SyS_perf_event_open+0x9/0x10 > [12573.374816] [<ffffffff816f4dd4>] tracesys+0xdd/0xe2 Notice the above trace. perf took its own ctx->lock, which can be taken while holding the rq lock. While holding this lock, it did a rcu_read_unlock(). The perf_lock_task_context() basically looks like: rcu_read_lock(); raw_spin_lock(ctx->lock); rcu_read_unlock(); Now, what looks to have happened, is that we scheduled after taking that first rcu_read_lock() but before taking the spin lock. When we scheduled back in and took the ctx->lock, the following rcu_read_unlock() triggered the "special" code. The rcu_read_unlock_special() takes the rnp->lock, which gives us a possible deadlock scenario. CPU0 CPU1 CPU2 ---- ---- ---- rcu_nocb_kthread() lock(rq->lock); lock(ctx->lock); lock(rnp->lock); wake_up(); lock(rq->lock); rcu_read_unlock(); rcu_read_unlock_special(); lock(rnp->lock); lock(ctx->lock); **** DEADLOCK **** > [12573.382068] > other info that might help us debug this: > > [12573.403229] Chain exists of: > rcu_node_0 --> &rq->lock --> &ctx->lock > > [12573.424471] Possible unsafe locking scenario: > > [12573.438499] CPU0 CPU1 > [12573.445599] ---- ---- > [12573.452691] lock(&ctx->lock); > [12573.459799] lock(&rq->lock); > [12573.467010] lock(&ctx->lock); > [12573.474192] lock(rcu_node_0); > [12573.481262] > *** DEADLOCK *** > > [12573.501931] 1 lock held by trinity-child17/31341: > [12573.508990] #0: (&ctx->lock){-.-...}, at: [<ffffffff811390ed>] perf_lock_task_context+0x7d/0x2d0 > [12573.516475] > stack backtrace: > [12573.530395] CPU: 1 PID: 31341 Comm: trinity-child17 Not tainted 3.10.0-rc3+ #39 > [12573.545357] ffffffff825b4f90 ffff880219f1dbc0 ffffffff816e375b ffff880219f1dc00 > [12573.552868] ffffffff816dfa5d ffff880219f1dc50 ffff88023ce4d1f8 ffff88023ce4ca40 > [12573.560353] 0000000000000001 0000000000000001 ffff88023ce4d1f8 ffff880219f1dcc0 > [12573.567856] Call Trace: > [12573.575011] [<ffffffff816e375b>] dump_stack+0x19/0x1b > [12573.582284] [<ffffffff816dfa5d>] print_circular_bug+0x200/0x20f > [12573.589637] [<ffffffff810b8d36>] __lock_acquire+0x1786/0x1af0 > [12573.596982] [<ffffffff810918f5>] ? sched_clock_cpu+0xb5/0x100 > [12573.604344] [<ffffffff810b9851>] lock_acquire+0x91/0x1f0 > [12573.611652] [<ffffffff811054ff>] ? rcu_read_unlock_special+0x9f/0x4c0 > [12573.619030] [<ffffffff816ebc90>] _raw_spin_lock+0x40/0x80 > [12573.626331] [<ffffffff811054ff>] ? rcu_read_unlock_special+0x9f/0x4c0 > [12573.633671] [<ffffffff811054ff>] rcu_read_unlock_special+0x9f/0x4c0 > [12573.640992] [<ffffffff811390ed>] ? perf_lock_task_context+0x7d/0x2d0 > [12573.648330] [<ffffffff810b429e>] ? put_lock_stats.isra.29+0xe/0x40 > [12573.655662] [<ffffffff813095a0>] ? delay_tsc+0x90/0xe0 > [12573.662964] [<ffffffff810760a6>] __rcu_read_unlock+0x96/0xa0 > [12573.670276] [<ffffffff811391b3>] perf_lock_task_context+0x143/0x2d0 > [12573.677622] [<ffffffff81139070>] ? __perf_event_enable+0x370/0x370 > [12573.684981] [<ffffffff8113938e>] find_get_context+0x4e/0x1f0 > [12573.692358] [<ffffffff811403f4>] SYSC_perf_event_open+0x514/0xbd0 > [12573.699753] [<ffffffff8108cd9d>] ? get_parent_ip+0xd/0x50 > [12573.707135] [<ffffffff810b71fd>] ? trace_hardirqs_on_caller+0xfd/0x1c0 > [12573.714599] [<ffffffff81140e49>] SyS_perf_event_open+0x9/0x10 > [12573.721996] [<ffffffff816f4dd4>] tracesys+0xdd/0xe2 This commit delays the wakeup via irq_work(), which is what perf and ftrace use to perform wakeups in critical sections. Reported-by: Dave Jones <davej@redhat.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2013-05-02Merge commit '8700c95adb03' into timers/nohzFrederic Weisbecker
The full dynticks tree needs the latest RCU and sched upstream updates in order to fix some dependencies. Merge a common upstream merge point that has these updates. Conflicts: include/linux/perf_event.h kernel/rcutree.h kernel/rcutree_plugin.h Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
2013-04-30Merge branch 'core-rcu-for-linus' of ↵Linus Torvalds
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip Pull RCU updates from Ingo Molnar: "The main changes in this cycle are mostly related to preparatory work for the full-dynticks work: - Remove restrictions on no-CBs CPUs, make RCU_FAST_NO_HZ take advantage of numbered callbacks, do callback accelerations based on numbered callbacks. Posted to LKML at https://lkml.org/lkml/2013/3/18/960 - RCU documentation updates. Posted to LKML at https://lkml.org/lkml/2013/3/18/570 - Miscellaneous fixes. Posted to LKML at https://lkml.org/lkml/2013/3/18/594" * 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (24 commits) rcu: Make rcu_accelerate_cbs() note need for future grace periods rcu: Abstract rcu_start_future_gp() from rcu_nocb_wait_gp() rcu: Rename n_nocb_gp_requests to need_future_gp rcu: Push lock release to rcu_start_gp()'s callers rcu: Repurpose no-CBs event tracing to future-GP events rcu: Rearrange locking in rcu_start_gp() rcu: Make RCU_FAST_NO_HZ take advantage of numbered callbacks rcu: Accelerate RCU callbacks at grace-period end rcu: Export RCU_FAST_NO_HZ parameters to sysfs rcu: Distinguish "rcuo" kthreads by RCU flavor rcu: Add event tracing for no-CBs CPUs' grace periods rcu: Add event tracing for no-CBs CPUs' callback registration rcu: Introduce proper blocking to no-CBs kthreads GP waits rcu: Provide compile-time control for no-CBs CPUs rcu: Tone down debugging during boot-up and shutdown. rcu: Add softirq-stall indications to stall-warning messages rcu: Documentation update rcu: Make bugginess of code sample more evident rcu: Fix hlist_bl_set_first_rcu() annotation rcu: Delete unused rcu_node "wakemask" field ...
2013-04-30kernel/: rename random32() to prandom_u32()Akinobu Mita
Use preferable function name which implies using a pseudo-random number generator. Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2013-04-19nohz: Ensure full dynticks CPUs are RCU nocbsFrederic Weisbecker
We need full dynticks CPU to also be RCU nocb so that we don't have to keep the tick to handle RCU callbacks. Make sure the range passed to nohz_full= boot parameter is a subset of rcu_nocbs= The CPUs that fail to meet this requirement will be excluded from the nohz_full range. This is checked early in boot time, before any CPU has the opportunity to stop its tick. Suggested-by: Steven Rostedt <rostedt@goodmis.org> Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Chris Metcalf <cmetcalf@tilera.com> Cc: Christoph Lameter <cl@linux.com> Cc: Geoff Levand <geoff@infradead.org> Cc: Gilad Ben Yossef <gilad@benyossef.com> Cc: Hakan Akkan <hakanakkan@gmail.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Kevin Hilman <khilman@linaro.org> Cc: Li Zhong <zhong@linux.vnet.ibm.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de>
2013-04-15rcu: Kick adaptive-ticks CPUs that are holding up RCU grace periodsPaul E. McKenney
Adaptive-ticks CPUs inform RCU when they enter kernel mode, but they do not necessarily turn the scheduler-clock tick back on. This state of affairs could result in RCU waiting on an adaptive-ticks CPU running for an extended period in kernel mode. Such a CPU will never run the RCU state machine, and could therefore indefinitely extend the RCU state machine, sooner or later resulting in an OOM condition. This patch, inspired by an earlier patch by Frederic Weisbecker, therefore causes RCU's force-quiescent-state processing to check for this condition and to send an IPI to CPUs that remain in that state for too long. "Too long" currently means about three jiffies by default, which is quite some time for a CPU to remain in the kernel without blocking. The rcu_tree.jiffies_till_first_fqs and rcutree.jiffies_till_next_fqs sysfs variables may be used to tune "too long" if needed. Reported-by: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Chris Metcalf <cmetcalf@tilera.com> Cc: Christoph Lameter <cl@linux.com> Cc: Geoff Levand <geoff@infradead.org> Cc: Gilad Ben Yossef <gilad@benyossef.com> Cc: Hakan Akkan <hakanakkan@gmail.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Kevin Hilman <khilman@linaro.org> Cc: Li Zhong <zhong@linux.vnet.ibm.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de>
2013-03-26Merge branches 'doc.2013.03.12a', 'fixes.2013.03.13a' and ↵Paul E. McKenney
'idlenocb.2013.03.26b' into HEAD doc.2013.03.12a: Documentation changes. fixes.2013.03.13a: Miscellaneous fixes. idlenocb.2013.03.26b: Remove restrictions on no-CBs CPUs, make RCU_FAST_NO_HZ take advantage of numbered callbacks, add callback acceleration based on numbered callbacks.
2013-03-26rcu: Make rcu_accelerate_cbs() note need for future grace periodsPaul E. McKenney
Now that rcu_start_future_gp() has been abstracted from rcu_nocb_wait_gp(), rcu_accelerate_cbs() can invoke rcu_start_future_gp() so as to register the need for any future grace periods needed by a CPU about to enter dyntick-idle mode. This commit makes this change. Note that some refactoring of rcu_start_gp() is carried out to avoid recursion and subsequent self-deadlocks. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2013-03-26rcu: Abstract rcu_start_future_gp() from rcu_nocb_wait_gp()Paul E. McKenney
CPUs going idle will need to record the need for a future grace period, but won't actually need to block waiting on it. This commit therefore splits rcu_start_future_gp(), which does the recording, from rcu_nocb_wait_gp(), which now invokes rcu_start_future_gp() to do the recording, after which rcu_nocb_wait_gp() does the waiting. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2013-03-26rcu: Push lock release to rcu_start_gp()'s callersPaul E. McKenney
If CPUs are to give prior notice of needed grace periods, it will be necessary to invoke rcu_start_gp() without dropping the root rcu_node structure's ->lock. This commit takes a second step in this direction by moving the release of this lock to rcu_start_gp()'s callers. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2013-03-26rcu: Rearrange locking in rcu_start_gp()Paul E. McKenney
If CPUs are to give prior notice of needed grace periods, it will be necessary to invoke rcu_start_gp() without dropping the root rcu_node structure's ->lock. This commit takes a first step in this direction by moving the release of this lock to the end of rcu_start_gp(). Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2013-03-26rcu: Make RCU_FAST_NO_HZ take advantage of numbered callbacksPaul E. McKenney
Because RCU callbacks are now associated with the number of the grace period that they must wait for, CPUs can now take advance callbacks corresponding to grace periods that ended while a given CPU was in dyntick-idle mode. This eliminates the need to try forcing the RCU state machine while entering idle, thus reducing the CPU intensiveness of RCU_FAST_NO_HZ, which should increase its energy efficiency. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2013-03-26rcu: Accelerate RCU callbacks at grace-period endPaul E. McKenney
Now that callback acceleration is idempotent, it is safe to accelerate callbacks during grace-period cleanup on any CPUs that the kthread happens to be running on. This commit therefore propagates the completion of the grace period to the per-CPU data structures, and also adds an rcu_advance_cbs() just before the cpu_needs_another_gp() check in order to reduce false-positive grace periods. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2013-03-26rcu: Distinguish "rcuo" kthreads by RCU flavorPaul E. McKenney
Currently, the per-no-CBs-CPU kthreads are named "rcuo" followed by the CPU number, for example, "rcuo". This is problematic given that there are either two or three RCU flavors, each of which gets a per-CPU kthread with exactly the same name. This commit therefore introduces a one-letter abbreviation for each RCU flavor, namely 'b' for RCU-bh, 'p' for RCU-preempt, and 's' for RCU-sched. This abbreviation is used to distinguish the "rcuo" kthreads, for example, for CPU 0 we would have "rcuob/0", "rcuop/0", and "rcuos/0". Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
2013-03-26rcu: Introduce proper blocking to no-CBs kthreads GP waitsPaul E. McKenney
Currently, the no-CBs kthreads do repeated timed waits for grace periods to elapse. This is crude and energy inefficient, so this commit allows no-CBs kthreads to specify exactly which grace period they are waiting for and also allows them to block for the entire duration until the desired grace period completes. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2013-03-13rcu: Tone down debugging during boot-up and shutdown.Paul E. McKenney
In some situations, randomly delaying RCU grace-period initialization can cause more trouble than help. This commit therefore restricts this type of RCU self-torture to runtime, giving it a rest during boot and shutdown. Reported-by: Sasha Levin <sasha.levin@oracle.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2013-03-12rcu: Remove comment referring to __stop_machine()Srivatsa S. Bhat
Although it used to be that CPU_DYING notifiers executed on the outgoing CPU with interrupts disabled and with all other CPUs spinning, this is no longer the case. This commit therefore removes this obsolete comment. Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2013-03-12rcu: Avoid invoking RCU core on offline CPUsPaul E. McKenney
Offline CPUs transition through the scheduler to the idle loop one last time before being shut down. This can result in RCU raising softirq on this CPU, which is at best useless given that the CPU's callbacks will be offloaded at CPU_DEAD time. This commit therefore avoids raising softirq on offline CPUs. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2013-03-12rcu: Fix spacing problemJiang Fang
Signed-off-by: Jiang Fang <jiang.xx.fang@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2013-03-12rcu: Remove restrictions on no-CBs CPUsPaul E. McKenney
Currently, CPU 0 is constrained to not be a no-CBs CPU, and furthermore at least one no-CBs CPU must remain online at any given time. These restrictions are problematic in some situations, such as cases where all CPUs must run a real-time workload that needs to be insulated from OS jitter and latencies due to RCU callback invocation. This commit therefore provides no-CBs CPUs a (very crude and energy-inefficient) way to start and to wait for grace periods independently of the normal RCU callback mechanisms. This approach allows any or all of the CPUs to be designated as no-CBs CPUs, and allows any proper subset of the CPUs (whether no-CBs CPUs or not) to be offlined. This commit also provides a fix for a locking bug spotted by Xie ChanglongX <changlongx.xie@intel.com>. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2013-01-29Merge branches 'doctorture.2013.01.29a', 'fixes.2013.01.26a', ↵Paul E. McKenney
'tagcb.2013.01.24a' and 'tiny.2013.01.29b' into HEAD doctorture.2013.01.11a: Changes to rcutorture and to RCU documentation. fixes.2013.01.26a: Miscellaneous fixes. tagcb.2013.01.24a: Tag RCU callbacks with grace-period number to simplify callback advancement. tiny.2013.01.29b: Enhancements to uniprocessor handling in tiny RCU.
2013-01-29rcu: Provide RCU CPU stall warnings for tiny RCUPaul E. McKenney
Tiny RCU has historically omitted RCU CPU stall warnings in order to reduce memory requirements, however, lack of these warnings caused Thomas Gleixner some debugging pain recently. Therefore, this commit adds RCU CPU stall warnings to tiny RCU if RCU_TRACE=y. This keeps the memory footprint small, while still enabling CPU stall warnings in kernels built to enable them. Updated to include Josh Triplett's suggested use of RCU_STALL_COMMON config variable to simplify #if expressions. Reported-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>