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On RT that code is preemptible, so we cannot assign NULL to timers
base as a preempter would spin forever in lock_timer_base().
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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People were complaining about broken balancing with the recent -rt
series.
A look at /proc/sched_debug yielded:
cpu#0, 2393.874 MHz
.nr_running : 0
.load : 0
.cpu_load[0] : 177522
.cpu_load[1] : 177522
.cpu_load[2] : 177522
.cpu_load[3] : 177522
.cpu_load[4] : 177522
cpu#1, 2393.874 MHz
.nr_running : 4
.load : 4096
.cpu_load[0] : 181618
.cpu_load[1] : 180850
.cpu_load[2] : 180274
.cpu_load[3] : 179938
.cpu_load[4] : 179758
Which indicated the cpu_load computation was hosed, the 177522 value
indicates that there is one RT task runnable. Initially I thought the
old problem of calculating the cpu_load from a softirq had re-surfaced,
however looking at the code shows its being done from scheduler_tick().
[ we really should fix this RT/cfs interaction some day... ]
A few trace_printk()s later:
sirq-timer/1-19 [001] 174.289744: 19: 50:S ==> [001] 0:140:R <idle>
<idle>-0 [001] 174.290724: enqueue_task_rt: adding task: 19/sirq-timer/1 with load: 177522
<idle>-0 [001] 174.290725: 0:140:R + [001] 19: 50:S sirq-timer/1
<idle>-0 [001] 174.290730: scheduler_tick: current load: 177522
<idle>-0 [001] 174.290732: scheduler_tick: current: 0/swapper
<idle>-0 [001] 174.290736: 0:140:R ==> [001] 19: 50:R sirq-timer/1
sirq-timer/1-19 [001] 174.290741: dequeue_task_rt: removing task: 19/sirq-timer/1 with load: 177522
sirq-timer/1-19 [001] 174.290743: 19: 50:S ==> [001] 0:140:R <idle>
We see that we always raise the timer softirq before doing the load
calculation. Avoid this by re-ordering the scheduler_tick() call in
update_process_times() to occur before we deal with timers.
This lowers the load back to sanity and restores regular load-balancing
behaviour.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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wake_up should do nothing on the nort, so we should use wakeup_timer_waiters,
also fix a spell mistake.
Cc: stable-rt@vger.kernel.org
Signed-off-by: Zhao Hongjiang <zhaohongjiang@huawei.com>
[bigeasy: s/CONFIG_PREEMPT_RT_BASE/CONFIG_PREEMPT_RT_FULL/]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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When softirqs can be preempted we need to make sure that cancelling
the timer from the active thread can not deadlock vs. a running timer
callback. Add a waitqueue to resolve that.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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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 uses of the __cpuinit macros from C files in
the core kernel directories (kernel, init, lib, mm, and include)
that don't really have a specific maintainer.
[1] https://lkml.org/lkml/2013/5/20/589
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
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Direct compare of jiffies related values does not work in the wrap
around case. Replace it with time_is_after_jiffies().
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Link: http://lkml.kernel.org/r/519BC066.5080600@acm.org
Cc: stable@vger.kernel.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull timer fixes from Thomas Gleixner:
- Cure for not using zalloc in the first place, which leads to random
crashes with CPUMASK_OFF_STACK.
- Revert a user space visible change which broke udev
- Add a missing cpu_online early return introduced by the new full
dyntick conversions
- Plug a long standing race in the timer wheel cpu hotplug code.
Sigh...
- Cleanup NOHZ per cpu data on cpu down to prevent stale data on cpu
up.
* 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
time: Revert ALWAYS_USE_PERSISTENT_CLOCK compile time optimizaitons
timer: Don't reinitialize the cpu base lock during CPU_UP_PREPARE
tick: Don't invoke tick_nohz_stop_sched_tick() if the cpu is offline
tick: Cleanup NOHZ per cpu data on cpu down
tick: Use zalloc_cpumask_var for allocating offstack cpumasks
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An inactive timer's base can refer to a offline cpu's base.
In the current code, cpu_base's lock is blindly reinitialized each
time a CPU is brought up. If a CPU is brought online during the period
that another thread is trying to modify an inactive timer on that CPU
with holding its timer base lock, then the lock will be reinitialized
under its feet. This leads to following SPIN_BUG().
<0> BUG: spinlock already unlocked on CPU#3, kworker/u:3/1466
<0> lock: 0xe3ebe000, .magic: dead4ead, .owner: kworker/u:3/1466, .owner_cpu: 1
<4> [<c0013dc4>] (unwind_backtrace+0x0/0x11c) from [<c026e794>] (do_raw_spin_unlock+0x40/0xcc)
<4> [<c026e794>] (do_raw_spin_unlock+0x40/0xcc) from [<c076c160>] (_raw_spin_unlock+0x8/0x30)
<4> [<c076c160>] (_raw_spin_unlock+0x8/0x30) from [<c009b858>] (mod_timer+0x294/0x310)
<4> [<c009b858>] (mod_timer+0x294/0x310) from [<c00a5e04>] (queue_delayed_work_on+0x104/0x120)
<4> [<c00a5e04>] (queue_delayed_work_on+0x104/0x120) from [<c04eae00>] (sdhci_msm_bus_voting+0x88/0x9c)
<4> [<c04eae00>] (sdhci_msm_bus_voting+0x88/0x9c) from [<c04d8780>] (sdhci_disable+0x40/0x48)
<4> [<c04d8780>] (sdhci_disable+0x40/0x48) from [<c04bf300>] (mmc_release_host+0x4c/0xb0)
<4> [<c04bf300>] (mmc_release_host+0x4c/0xb0) from [<c04c7aac>] (mmc_sd_detect+0x90/0xfc)
<4> [<c04c7aac>] (mmc_sd_detect+0x90/0xfc) from [<c04c2504>] (mmc_rescan+0x7c/0x2c4)
<4> [<c04c2504>] (mmc_rescan+0x7c/0x2c4) from [<c00a6a7c>] (process_one_work+0x27c/0x484)
<4> [<c00a6a7c>] (process_one_work+0x27c/0x484) from [<c00a6e94>] (worker_thread+0x210/0x3b0)
<4> [<c00a6e94>] (worker_thread+0x210/0x3b0) from [<c00aad9c>] (kthread+0x80/0x8c)
<4> [<c00aad9c>] (kthread+0x80/0x8c) from [<c000ea80>] (kernel_thread_exit+0x0/0x8)
As an example, this particular crash occurred when CPU #3 is executing
mod_timer() on an inactive timer whose base is refered to offlined CPU
#2. The code locked the timer_base corresponding to CPU #2. Before it
could proceed, CPU #2 came online and reinitialized the spinlock
corresponding to its base. Thus now CPU #3 held a lock which was
reinitialized. When CPU #3 finally ended up unlocking the old cpu_base
corresponding to CPU #2, we hit the above SPIN_BUG().
CPU #0 CPU #3 CPU #2
------ ------- -------
..... ...... <Offline>
mod_timer()
lock_timer_base
spin_lock_irqsave(&base->lock)
cpu_up(2) ..... ......
init_timers_cpu()
.... ..... spin_lock_init(&base->lock)
..... spin_unlock_irqrestore(&base->lock) ......
<spin_bug>
Allocation of per_cpu timer vector bases is done only once under
"tvec_base_done[]" check. In the current code, spinlock_initialization
of base->lock isn't under this check. When a CPU is up each time the
base lock is reinitialized. Move base spinlock initialization under
the check.
Signed-off-by: Tirupathi Reddy <tirupath@codeaurora.org>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/1368520142-4136-1-git-send-email-tirupath@codeaurora.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull 'full dynticks' support from Ingo Molnar:
"This tree from Frederic Weisbecker adds a new, (exciting! :-) core
kernel feature to the timer and scheduler subsystems: 'full dynticks',
or CONFIG_NO_HZ_FULL=y.
This feature extends the nohz variable-size timer tick feature from
idle to busy CPUs (running at most one task) as well, potentially
reducing the number of timer interrupts significantly.
This feature got motivated by real-time folks and the -rt tree, but
the general utility and motivation of full-dynticks runs wider than
that:
- HPC workloads get faster: CPUs running a single task should be able
to utilize a maximum amount of CPU power. A periodic timer tick at
HZ=1000 can cause a constant overhead of up to 1.0%. This feature
removes that overhead - and speeds up the system by 0.5%-1.0% on
typical distro configs even on modern systems.
- Real-time workload latency reduction: CPUs running critical tasks
should experience as little jitter as possible. The last remaining
source of kernel-related jitter was the periodic timer tick.
- A single task executing on a CPU is a pretty common situation,
especially with an increasing number of cores/CPUs, so this feature
helps desktop and mobile workloads as well.
The cost of the feature is mainly related to increased timer
reprogramming overhead when a CPU switches its tick period, and thus
slightly longer to-idle and from-idle latency.
Configuration-wise a third mode of operation is added to the existing
two NOHZ kconfig modes:
- CONFIG_HZ_PERIODIC: [formerly !CONFIG_NO_HZ], now explicitly named
as a config option. This is the traditional Linux periodic tick
design: there's a HZ tick going on all the time, regardless of
whether a CPU is idle or not.
- CONFIG_NO_HZ_IDLE: [formerly CONFIG_NO_HZ=y], this turns off the
periodic tick when a CPU enters idle mode.
- CONFIG_NO_HZ_FULL: this new mode, in addition to turning off the
tick when a CPU is idle, also slows the tick down to 1 Hz (one
timer interrupt per second) when only a single task is running on a
CPU.
The .config behavior is compatible: existing !CONFIG_NO_HZ and
CONFIG_NO_HZ=y settings get translated to the new values, without the
user having to configure anything. CONFIG_NO_HZ_FULL is turned off by
default.
This feature is based on a lot of infrastructure work that has been
steadily going upstream in the last 2-3 cycles: related RCU support
and non-periodic cputime support in particular is upstream already.
This tree adds the final pieces and activates the feature. The pull
request is marked RFC because:
- it's marked 64-bit only at the moment - the 32-bit support patch is
small but did not get ready in time.
- it has a number of fresh commits that came in after the merge
window. The overwhelming majority of commits are from before the
merge window, but still some aspects of the tree are fresh and so I
marked it RFC.
- it's a pretty wide-reaching feature with lots of effects - and
while the components have been in testing for some time, the full
combination is still not very widely used. That it's default-off
should reduce its regression abilities and obviously there are no
known regressions with CONFIG_NO_HZ_FULL=y enabled either.
- the feature is not completely idempotent: there is no 100%
equivalent replacement for a periodic scheduler/timer tick. In
particular there's ongoing work to map out and reduce its effects
on scheduler load-balancing and statistics. This should not impact
correctness though, there are no known regressions related to this
feature at this point.
- it's a pretty ambitious feature that with time will likely be
enabled by most Linux distros, and we'd like you to make input on
its design/implementation, if you dislike some aspect we missed.
Without flaming us to crisp! :-)
Future plans:
- there's ongoing work to reduce 1Hz to 0Hz, to essentially shut off
the periodic tick altogether when there's a single busy task on a
CPU. We'd first like 1 Hz to be exposed more widely before we go
for the 0 Hz target though.
- once we reach 0 Hz we can remove the periodic tick assumption from
nr_running>=2 as well, by essentially interrupting busy tasks only
as frequently as the sched_latency constraints require us to do -
once every 4-40 msecs, depending on nr_running.
I am personally leaning towards biting the bullet and doing this in
v3.10, like the -rt tree this effort has been going on for too long -
but the final word is up to you as usual.
More technical details can be found in Documentation/timers/NO_HZ.txt"
* 'timers-nohz-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (39 commits)
sched: Keep at least 1 tick per second for active dynticks tasks
rcu: Fix full dynticks' dependency on wide RCU nocb mode
nohz: Protect smp_processor_id() in tick_nohz_task_switch()
nohz_full: Add documentation.
cputime_nsecs: use math64.h for nsec resolution conversion helpers
nohz: Select VIRT_CPU_ACCOUNTING_GEN from full dynticks config
nohz: Reduce overhead under high-freq idling patterns
nohz: Remove full dynticks' superfluous dependency on RCU tree
nohz: Fix unavailable tick_stop tracepoint in dynticks idle
nohz: Add basic tracing
nohz: Select wide RCU nocb for full dynticks
nohz: Disable the tick when irq resume in full dynticks CPU
nohz: Re-evaluate the tick for the new task after a context switch
nohz: Prepare to stop the tick on irq exit
nohz: Implement full dynticks kick
nohz: Re-evaluate the tick from the scheduler IPI
sched: New helper to prevent from stopping the tick in full dynticks
sched: Kick full dynticks CPU that have more than one task enqueued.
perf: New helper to prevent full dynticks CPUs from stopping tick
perf: Kick full dynticks CPU if events rotation is needed
...
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Andrew Morton noted:
akpm3:/usr/src/25> grep SYSCALL kernel/timer.c
SYSCALL_DEFINE1(alarm, unsigned int, seconds)
SYSCALL_DEFINE0(getpid)
SYSCALL_DEFINE0(getppid)
SYSCALL_DEFINE0(getuid)
SYSCALL_DEFINE0(geteuid)
SYSCALL_DEFINE0(getgid)
SYSCALL_DEFINE0(getegid)
SYSCALL_DEFINE0(gettid)
SYSCALL_DEFINE1(sysinfo, struct sysinfo __user *, info)
COMPAT_SYSCALL_DEFINE1(sysinfo, struct compat_sysinfo __user *, info)
Only one of those should be in kernel/timer.c. Who wrote this thing?
[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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The only use outside of kernel/timer.c was in kernel/compat.c, so move
compat_sys_sysinfo() next to sys_sysinfo() in kernel/timer.c.
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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We are planning to convert the dynticks Kconfig options layout
into a choice menu. The user must be able to easily pick
any of the following implementations: constant periodic tick,
idle dynticks, full dynticks.
As this implies a mutual exclusion, the two dynticks implementions
need to converge on the selection of a common Kconfig option in order
to ease the sharing of a common infrastructure.
It would thus seem pretty natural to reuse CONFIG_NO_HZ to
that end. It already implements all the idle dynticks code
and the full dynticks depends on all that code for now.
So ideally the choice menu would propose CONFIG_NO_HZ_IDLE and
CONFIG_NO_HZ_EXTENDED then both would select CONFIG_NO_HZ.
On the other hand we want to stay backward compatible: if
CONFIG_NO_HZ is set in an older config file, we want to
enable CONFIG_NO_HZ_IDLE by default.
But we can't afford both at the same time or we run into
a circular dependency:
1) CONFIG_NO_HZ_IDLE and CONFIG_NO_HZ_EXTENDED both select
CONFIG_NO_HZ
2) If CONFIG_NO_HZ is set, we default to CONFIG_NO_HZ_IDLE
We might be able to support that from Kconfig/Kbuild but it
may not be wise to introduce such a confusing behaviour.
So to solve this, create a new CONFIG_NO_HZ_COMMON option
which gathers the common code between idle and full dynticks
(that common code for now is simply the idle dynticks code)
and select it from their referring Kconfig.
Then we'll later create CONFIG_NO_HZ_IDLE and map CONFIG_NO_HZ
to it for backward compatibility.
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: Namhyung Kim <namhyung.kim@lge.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>
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Wake up a CPU when a timer list timer is enqueued there and
the target is part of the full dynticks range. Sending an IPI
to it makes it reconsidering the next timer to program on top
of recent updates.
This may later be improved by checking if the tick is really
stopped on the target. This would need some careful
synchronization though. So deal with such optimization later
and start simple.
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: Namhyung Kim <namhyung.kim@lge.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>
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull scheduler changes from Ingo Molnar:
"Main changes:
- scheduler side full-dynticks (user-space execution is undisturbed
and receives no timer IRQs) preparation changes that convert the
cputime accounting code to be full-dynticks ready, from Frederic
Weisbecker.
- Initial sched.h split-up changes, by Clark Williams
- select_idle_sibling() performance improvement by Mike Galbraith:
" 1 tbench pair (worst case) in a 10 core + SMT package:
pre 15.22 MB/sec 1 procs
post 252.01 MB/sec 1 procs "
- sched_rr_get_interval() ABI fix/change. We think this detail is not
used by apps (so it's not an ABI in practice), but lets keep it
under observation.
- misc RT scheduling cleanups, optimizations"
* 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (24 commits)
sched/rt: Add <linux/sched/rt.h> header to <linux/init_task.h>
cputime: Remove irqsave from seqlock readers
sched, powerpc: Fix sched.h split-up build failure
cputime: Restore CPU_ACCOUNTING config defaults for PPC64
sched/rt: Move rt specific bits into new header file
sched/rt: Add a tuning knob to allow changing SCHED_RR timeslice
sched: Move sched.h sysctl bits into separate header
sched: Fix signedness bug in yield_to()
sched: Fix select_idle_sibling() bouncing cow syndrome
sched/rt: Further simplify pick_rt_task()
sched/rt: Do not account zero delta_exec in update_curr_rt()
cputime: Safely read cputime of full dynticks CPUs
kvm: Prepare to add generic guest entry/exit callbacks
cputime: Use accessors to read task cputime stats
cputime: Allow dynamic switch between tick/virtual based cputime accounting
cputime: Generic on-demand virtual cputime accounting
cputime: Move default nsecs_to_cputime() to jiffies based cputime file
cputime: Librarize per nsecs resolution cputime definitions
cputime: Avoid multiplication overflow on utime scaling
context_tracking: Export context state for generic vtime
...
Fix up conflict in kernel/context_tracking.c due to comment additions.
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Move the sysctl-related bits from include/linux/sched.h into
a new file: include/linux/sched/sysctl.h. Then update source
files requiring access to those bits by including the new
header file.
Signed-off-by: Clark Williams <williams@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/20130207094659.06dced96@riff.lan
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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klogd is woken up asynchronously from the tick in order
to do it safely.
However if printk is called when the tick is stopped, the reader
won't be woken up until the next interrupt, which might not fire
for a while. As a result, the user may miss some message.
To fix this, lets implement the printk tick using a lazy irq work.
This subsystem takes care of the timer tick state and can
fix up accordingly.
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
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Adding two (or more) timers with large values for "expires" (they have
to reside within tv5 in the same list) leads to endless looping
between cascade() and internal_add_timer() in case CONFIG_BASE_SMALL
is one and jiffies are crossing the value 1 << 18. The bug was
introduced between 2.6.11 and 2.6.12 (and survived for quite some
time).
This patch ensures that when cascade() is called timers within tv5 are
not added endlessly to their own list again, instead they are added to
the next lower tv level tv4 (as expected).
Signed-off-by: Christian Hildner <christian.hildner@siemens.com>
Reviewed-by: Jan Kiszka <jan.kiszka@siemens.com>
Link: http://lkml.kernel.org/r/98673C87CB31274881CFFE0B65ECC87B0F5FC1963E@DEFTHW99EA4MSX.ww902.siemens.net
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
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into timers/core
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Timer internals are protected with irq-safe locks but timer execution
isn't, so a timer being dequeued for execution and its execution
aren't atomic against IRQs. This makes it impossible to wait for its
completion from IRQ handlers and difficult to shoot down a timer from
IRQ handlers.
This issue caused some issues for delayed_work interface. Because
there's no way to reliably shoot down delayed_work->timer from IRQ
handlers, __cancel_delayed_work() can't share the logic to steal the
target delayed_work with cancel_delayed_work_sync(), and can only
steal delayed_works which are on queued on timer. Similarly, the
pending mod_delayed_work() can't be used from IRQ handlers.
This patch adds a new timer flag TIMER_IRQSAFE, which makes the timer
to be executed without enabling IRQ after dequeueing such that its
dequeueing and execution are atomic against IRQ handlers.
This makes it safe to wait for the timer's completion from IRQ
handlers, for example, using del_timer_sync(). It can never be
executing on the local CPU and if executing on other CPUs it won't be
interrupted until done.
This will enable simplifying delayed_work cancel/mod interface.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: torvalds@linux-foundation.org
Cc: peterz@infradead.org
Link: http://lkml.kernel.org/r/1344449428-24962-5-git-send-email-tj@kernel.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
|
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Over time, timer initializers became messy with unnecessarily
duplicated code which are inconsistently spread across timer.h and
timer.c.
This patch cleans up timer initializers.
* timer.c::__init_timer() is renamed to do_init_timer().
* __TIMER_INITIALIZER() added. It takes @flags and all initializers
are wrappers around it.
* init_timer[_on_stack]_key() now take @flags.
* __init_timer[_on_stack]() added. They take @flags and all init
macros are wrappers around them.
* __setup_timer[_on_stack]() added. It uses __init_timer() and takes
@flags. All setup macros are wrappers around the two.
Note that this patch doesn't add missing init/setup combinations -
e.g. init_timer_deferrable_on_stack(). Adding missing ones is
trivial.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: torvalds@linux-foundation.org
Cc: peterz@infradead.org
Link: http://lkml.kernel.org/r/1344449428-24962-4-git-send-email-tj@kernel.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
|
|
To prepare for addition of another flag, generalize timer->base flags
handling.
* Rename from TBASE_*_FLAG to TIMER_* and make them LU constants.
* Define and use TIMER_FLAG_MASK for flags masking so that multiple
flags can be handled correctly.
* Don't dereference timer->base directly even if
!tbase_get_deferrable(). All two such places are already passed in
@base, so use it instead.
* Make sure tvec_base's alignment is large enough for timer->base
flags using BUILD_BUG_ON().
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: torvalds@linux-foundation.org
Cc: peterz@infradead.org
Link: http://lkml.kernel.org/r/1344449428-24962-2-git-send-email-tj@kernel.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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New helper: current_thread_info(). Allows to do a bunch of odd syscalls
in C. While we are at it, there had never been a reason to do
osf_getpriority() in assembler. We also get "namespace"-aware (read:
consistent with getuid(2), etc.) behaviour from getx?id() syscalls now.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Michael Cree <mcree@orcon.net.nz>
Acked-by: Matt Turner <mattst88@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Gilad reported at
http://lkml.kernel.org/r/1336056962-10465-2-git-send-email-gilad@benyossef.com
"Current timer code fails to correctly return a value meaning that
there is no future timer event, with the result that the timer keeps
getting re-armed in HZ one shot mode even when we could turn it off,
generating unneeded interrupts.
What is happening is that when __next_timer_interrupt() wishes
to return a value that signifies "there is no future timer
event", it returns (base->timer_jiffies + NEXT_TIMER_MAX_DELTA).
However, the code in tick_nohz_stop_sched_tick(), which called
__next_timer_interrupt() via get_next_timer_interrupt(),
compares the return value to (last_jiffies + NEXT_TIMER_MAX_DELTA)
to see if the timer needs to be re-armed.
base->timer_jiffies != last_jiffies and so tick_nohz_stop_sched_tick()
interperts the return value as indication that there is a distant
future event 12 days from now and programs the timer to fire next
after KTIME_MAX nsecs instead of avoiding to arm it. This ends up
causing a needless interrupt once every KTIME_MAX nsecs."
Fix this by using the new active timer accounting. This avoids scans
when no active timer is enqueued completely, so we don't have to rely
on base->timer_next and base->timer_jiffies anymore.
Reported-by: Gilad Ben-Yossef <gilad@benyossef.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Link: http://lkml.kernel.org/r/20120525214819.317535385@linutronix.de
|
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The code in get_next_timer_interrupt() is suboptimal as it has to run
through the cascade to find the next expiring timer. On a completely
idle core we should only do that when there is an active timer
enqueued and base->next_timer does not give us a fast answer.
Add accounting of the active timers to the now consolidated
attach/detach code. I deliberately avoided sanity checks because the
code is fully symetric and any fiddling with timers w/o using the API
functions will lead to cute explosions anyway. ulong is big enough
even on 32bit and if we really run into the situation to have more
than 1<<32 timers enqueued there, then we are definitely not in a
state to go idle and run through that code.
This allows us to fix another shortcoming of get_next_timer_interrupt().
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Gilad Ben-Yossef <gilad@benyossef.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Link: http://lkml.kernel.org/r/20120525214819.236377028@linutronix.de
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Another bunch of mindlessly copied code. All callers of
internal_add_timer() except the recascading code updates
base->next_timer.
Move this into internal_add_timer() and let the cascading code call
__internal_add_timer().
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Gilad Ben-Yossef <gilad@benyossef.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Link: http://lkml.kernel.org/r/20120525214819.189946224@linutronix.de
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|
Most callers of detach_timer() have the same pattern around
them. Check whether the timer is pending and eventually updating
base->next_timer.
Create detach_if_pending() and replace the duplicated code.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Gilad Ben-Yossef <gilad@benyossef.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Link: http://lkml.kernel.org/r/20120525214819.131246037@linutronix.de
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|
git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace
Pull user namespace enhancements from Eric Biederman:
"This is a course correction for the user namespace, so that we can
reach an inexpensive, maintainable, and reasonably complete
implementation.
Highlights:
- Config guards make it impossible to enable the user namespace and
code that has not been converted to be user namespace safe.
- Use of the new kuid_t type ensures the if you somehow get past the
config guards the kernel will encounter type errors if you enable
user namespaces and attempt to compile in code whose permission
checks have not been updated to be user namespace safe.
- All uids from child user namespaces are mapped into the initial
user namespace before they are processed. Removing the need to add
an additional check to see if the user namespace of the compared
uids remains the same.
- With the user namespaces compiled out the performance is as good or
better than it is today.
- For most operations absolutely nothing changes performance or
operationally with the user namespace enabled.
- The worst case performance I could come up with was timing 1
billion cache cold stat operations with the user namespace code
enabled. This went from 156s to 164s on my laptop (or 156ns to
164ns per stat operation).
- (uid_t)-1 and (gid_t)-1 are reserved as an internal error value.
Most uid/gid setting system calls treat these value specially
anyway so attempting to use -1 as a uid would likely cause
entertaining failures in userspace.
- If setuid is called with a uid that can not be mapped setuid fails.
I have looked at sendmail, login, ssh and every other program I
could think of that would call setuid and they all check for and
handle the case where setuid fails.
- If stat or a similar system call is called from a context in which
we can not map a uid we lie and return overflowuid. The LFS
experience suggests not lying and returning an error code might be
better, but the historical precedent with uids is different and I
can not think of anything that would break by lying about a uid we
can't map.
- Capabilities are localized to the current user namespace making it
safe to give the initial user in a user namespace all capabilities.
My git tree covers all of the modifications needed to convert the core
kernel and enough changes to make a system bootable to runlevel 1."
Fix up trivial conflicts due to nearby independent changes in fs/stat.c
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace: (46 commits)
userns: Silence silly gcc warning.
cred: use correct cred accessor with regards to rcu read lock
userns: Convert the move_pages, and migrate_pages permission checks to use uid_eq
userns: Convert cgroup permission checks to use uid_eq
userns: Convert tmpfs to use kuid and kgid where appropriate
userns: Convert sysfs to use kgid/kuid where appropriate
userns: Convert sysctl permission checks to use kuid and kgids.
userns: Convert proc to use kuid/kgid where appropriate
userns: Convert ext4 to user kuid/kgid where appropriate
userns: Convert ext3 to use kuid/kgid where appropriate
userns: Convert ext2 to use kuid/kgid where appropriate.
userns: Convert devpts to use kuid/kgid where appropriate
userns: Convert binary formats to use kuid/kgid where appropriate
userns: Add negative depends on entries to avoid building code that is userns unsafe
userns: signal remove unnecessary map_cred_ns
userns: Teach inode_capable to understand inodes whose uids map to other namespaces.
userns: Fail exec for suid and sgid binaries with ids outside our user namespace.
userns: Convert stat to return values mapped from kuids and kgids
userns: Convert user specfied uids and gids in chown into kuids and kgid
userns: Use uid_eq gid_eq helpers when comparing kuids and kgids in the vfs
...
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Pull workqueue changes from Tejun Heo:
"Nothing exciting. Most are updates to debug stuff and related fixes.
Two not-too-critical bugs are fixed - WARN_ON() triggering spurious
during cpu offlining and unlikely lockdep related oops."
* 'for-3.5' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq:
lockdep: fix oops in processing workqueue
workqueue: skip nr_running sanity check in worker_enter_idle() if trustee is active
workqueue: Catch more locking problems with flush_work()
workqueue: change BUG_ON() to WARN_ON()
trace: Remove unused workqueue tracer
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Under memory load, on x86_64, with lockdep enabled, the workqueue's
process_one_work() has been seen to oops in __lock_acquire(), barfing
on a 0xffffffff00000000 pointer in the lockdep_map's class_cache[].
Because it's permissible to free a work_struct from its callout function,
the map used is an onstack copy of the map given in the work_struct: and
that copy is made without any locking.
Surprisingly, gcc (4.5.1 in Hugh's case) uses "rep movsl" rather than
"rep movsq" for that structure copy: which might race with a workqueue
user's wait_on_work() doing lock_map_acquire() on the source of the
copy, putting a pointer into the class_cache[], but only in time for
the top half of that pointer to be copied to the destination map.
Boom when process_one_work() subsequently does lock_map_acquire()
on its onstack copy of the lockdep_map.
Fix this, and a similar instance in call_timer_fn(), with a
lockdep_copy_map() function which additionally NULLs the class_cache[].
Note: this oops was actually seen on 3.4-next, where flush_work() newly
does the racing lock_map_acquire(); but Tejun points out that 3.4 and
earlier are already vulnerable to the same through wait_on_work().
* Patch orginally from Peter. Hugh modified it a bit and wrote the
description.
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Reported-by: Hugh Dickins <hughd@google.com>
LKML-Reference: <alpine.LSU.2.00.1205070951170.1544@eggly.anvils>
Signed-off-by: Tejun Heo <tj@kernel.org>
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kgid
Convert setregid, setgid, setreuid, setuid,
setresuid, getresuid, setresgid, getresgid, setfsuid, setfsgid,
getuid, geteuid, getgid, getegid,
waitpid, waitid, wait4.
Convert userspace uids and gids into kuids and kgids before
being placed on struct cred. Convert struct cred kuids and
kgids into userspace uids and gids when returning them.
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
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The mod_timer_pinned() header comment states that it prevents timers
from being migrated to a different CPU. This is not the case, instead,
it ensures that the timer is posted to the current CPU, but does nothing
to prevent CPU-hotplug operations from migrating the timer.
This commit therefore brings the comment header into alignment with
reality.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
* 'core-debugobjects-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
timer: Use debugobjects to catch deletion of uninitialized timers
timer: Setup uninitialized timer with a stub callback
debugobjects: Extend to assert that an object is initialized
debugobjects: Be smarter about static objects
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In order to safely dereference current->real_parent inside an
rcu_read_lock, we need an rcu_dereference.
Signed-off-by: Mandeep Singh Baines <msb@chromium.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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del_timer_sync() calls debug_object_assert_init() to assert that
a timer has been initialized before calling lock_timer_base().
lock_timer_base() would spin forever on a NULL(uninit-ed) base.
The check is added to del_timer() to prevent silent failure, even
though it would not get stuck in an infinite loop.
[ sboyd@codeaurora.org: Remove WARN, intialize timer function]
Signed-off-by: Christine Chan <cschan@codeaurora.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Cc: John Stultz <john.stultz@linaro.org>
Link: http://lkml.kernel.org/r/1320724108-20788-4-git-send-email-sboyd@codeaurora.org
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Remove the WARN_ON() in timer_fixup_activate() as we now get the
debugobjects printout in the debugobjects activate check.
We also assign a dummy timer callback so that if the timer is
actually set to fire we don't oops.
[ tglx@linutronix.de: Split out the debugobjects vs. the timer change ]
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Cc: Christine Chan <cschan@codeaurora.org>
Cc: John Stultz <john.stultz@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/1320724108-20788-2-git-send-email-sboyd@codeaurora.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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The changed files were only including linux/module.h for the
EXPORT_SYMBOL infrastructure, and nothing else. Revector them
onto the isolated export header for faster compile times.
Nothing to see here but a whole lot of instances of:
-#include <linux/module.h>
+#include <linux/export.h>
This commit is only changing the kernel dir; next targets
will probably be mm, fs, the arch dirs, etc.
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
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There is an optimization which does not update the timer if the timer
was pending and the expiration time was unchanged.
Since commit 3bbb9ec9 ("timers: Introduce the concept of timer slack
for legacy timers") this optimization is no longer applied for timers
where the expiration time got extended due to the slack value. So we
need to check again after the expiration time might have been updated.
[ tglx: Made it a single check by applying slack first and sorting
out the slack = 0 value (all timeouts < 256 jiffies) early ]
Signed-off-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Link: http://lkml.kernel.org/r/20110521105828.GA29442@Chamillionaire.breakpoint.cc
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
* 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: (62 commits)
posix-clocks: Check write permissions in posix syscalls
hrtimer: Remove empty hrtimer_init_hres_timer()
hrtimer: Update hrtimer->state documentation
hrtimer: Update base[CLOCK_BOOTTIME].offset correctly
timers: Export CLOCK_BOOTTIME via the posix timers interface
timers: Add CLOCK_BOOTTIME hrtimer base
time: Extend get_xtime_and_monotonic_offset() to also return sleep
time: Introduce get_monotonic_boottime and ktime_get_boottime
hrtimers: extend hrtimer base code to handle more then 2 clockids
ntp: Remove redundant and incorrect parameter check
mn10300: Switch do_timer() to xtimer_update()
posix clocks: Introduce dynamic clocks
posix-timers: Cleanup namespace
posix-timers: Add support for fd based clocks
x86: Add clock_adjtime for x86
posix-timers: Introduce a syscall for clock tuning.
time: Splitout compat timex accessors
ntp: Add ADJ_SETOFFSET mode bit
time: Introduce timekeeping_inject_offset
posix-timer: Update comment
...
Fix up new system-call-related conflicts in
arch/x86/ia32/ia32entry.S
arch/x86/include/asm/unistd_32.h
arch/x86/include/asm/unistd_64.h
arch/x86/kernel/syscall_table_32.S
(name_to_handle_at()/open_by_handle_at() vs clock_adjtime()), and some
due to movement of get_jiffies_64() in:
kernel/time.c
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
* 'core-locking-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
rtmutex: tester: Remove the remaining BKL leftovers
lockdep/timers: Explain in detail the locking problems del_timer_sync() may cause
rtmutex: Simplify PI algorithm and make highest prio task get lock
rwsem: Remove redundant asmregparm annotation
rwsem: Move duplicate function prototypes to linux/rwsem.h
rwsem: Unify the duplicate rwsem_is_locked() inlines
rwsem: Move duplicate init macros and functions to linux/rwsem.h
rwsem: Move duplicate struct rwsem declaration to linux/rwsem.h
x86: Cleanup rwsem_count_t typedef
rwsem: Cleanup includes
locking: Remove deprecated lock initializers
cred: Replace deprecated spinlock initialization
kthread: Replace deprecated spinlock initialization
xtensa: Replace deprecated spinlock initialization
um: Replace deprecated spinlock initialization
sparc: Replace deprecated spinlock initialization
mips: Replace deprecated spinlock initialization
cris: Replace deprecated spinlock initialization
alpha: Replace deprecated spinlock initialization
rtmutex-tester: Remove BKL tests
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In complex subsystems like mac80211 structures can contain several
timers and work structs, so identifying a specific instance from the
call trace and object type output of debugobjects can be hard.
Allow the subsystems which support debugobjects to provide a hint
function. This function returns a pointer to a kernel address
(preferrably the objects callback function) which is printed along
with the debugobjects type.
Add hint methods for timer_list, work_struct and hrtimer.
[ tglx: Massaged changelog, made it compile ]
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
LKML-Reference: <20110307085809.GA9334@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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cause
Twice I had to explain the output about why lockdep gives an error with
locks in IRQ context and with del_timer_sync(). Might as well write it
up and place it in the comments above the code in del_timer_sync().
Perhaps the next time this lockdep dump triggers people will understand
the issues.
It is a ticky issue and very subtle, explaining it in detail in the code
may help others understand the issue when they stumble upon the bug
again.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1297186794.23343.19.camel@gandalf.stny.rr.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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Both attempts at trying to allow softirq usage for
del_timer_sync() failed (produced bogus warnings),
so revert the commit for this release:
f266a5110d45: lockdep, timer: Fix del_timer_sync() annotation
and try again later.
Reported-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Yong Zhang <yong.zhang0@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
LKML-Reference: <1297174680.13327.107.camel@laptop>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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Calling local_bh_enable() will want to actually start processing
softirqs, which isn't a good idea since this can get called with IRQs
disabled.
Cure this by using _local_bh_enable() which doesn't start processing
softirqs, and use raw_local_irq_save() to avoid any softirqs from
happening without letting lockdep think IRQs are in fact disabled.
Reported-by: Nick Bowler <nbowler@elliptictech.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Reviewed-by: Yong Zhang <yong.zhang0@gmail.com>
LKML-Reference: <20110203141548.039540914@chello.nl>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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do_timer() is primary timekeeping related. calc_global_load() is
called from do_timer() as well, but that's more for historical
reasons.
[ tglx: Fixed up the calc_global_load() reject andmassaged changelog ]
Signed-off-by: Torben Hohn <torbenh@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: johnstul@us.ibm.com
Cc: yong.zhang0@gmail.com
Cc: hch@infradead.org
LKML-Reference: <20110127145855.23248.56933.stgit@localhost>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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|
git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
* 'timers-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
MAINTAINERS: Update timer related entries
timers: Use this_cpu_read
timerqueue: Make timerqueue_getnext() static inline
hrtimer: fix timerqueue conversion flub
hrtimers: Convert hrtimers to use timerlist infrastructure
timers: Fixup allmodconfig build issue
timers: Rename timerlist infrastructure to timerqueue
timers: Introduce timerlist infrastructure.
hrtimer: Remove stale comment on curr_timer
timer: Warn when del_timer_sync() is called in hardirq context
timer: Del_timer_sync() can be used in softirq context
timer: Make try_to_del_timer_sync() the same on SMP and UP
posix-timers: Annotate lock_timer()
timer: Permit statically-declared work with deferrable timers
time: Use ARRAY_SIZE macro in timecompare.c
timer: Initialize the field slack of timer_list
timer_list: Remove alignment padding on 64 bit when CONFIG_TIMER_STATS
time: Compensate for rounding on odd-frequency clocksources
Fix up trivial conflict in MAINTAINERS
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Eric asked for this.
[tglx: Because it generates faster code according to Erics ]
Signed-off-by: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: linux-mm@kvack.org
LKML-Reference: <alpine.DEB.2.00.1011301404490.4039@router.home>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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This fixes a bug as seen on 2.6.32 based kernels where timers got
enqueued on offline cpus.
If a cpu goes offline it might still have pending timers. These will
be migrated during CPU_DEAD handling after the cpu is offline.
However while the cpu is going offline it will schedule the idle task
which will then call tick_nohz_stop_sched_tick().
That function in turn will call get_next_timer_intterupt() to figure
out if the tick of the cpu can be stopped or not. If it turns out that
the next tick is just one jiffy off (delta_jiffies == 1)
tick_nohz_stop_sched_tick() incorrectly assumes that the tick should
not stop and takes an early exit and thus it won't update the load
balancer cpu.
Just afterwards the cpu will be killed and the load balancer cpu could
be the offline cpu.
On 2.6.32 based kernel get_nohz_load_balancer() gets called to decide
on which cpu a timer should be enqueued (see __mod_timer()). Which
leads to the possibility that timers get enqueued on an offline cpu.
These will never expire and can cause a system hang.
This has been observed 2.6.32 kernels. On current kernels
__mod_timer() uses get_nohz_timer_target() which doesn't have that
problem. However there might be other problems because of the too
early exit tick_nohz_stop_sched_tick() in case a cpu goes offline.
The easiest and probably safest fix seems to be to let
get_next_timer_interrupt() just lie and let it say there isn't any
pending timer if the current cpu is offline.
I also thought of moving migrate_[hr]timers() from CPU_DEAD to
CPU_DYING, but seeing that there already have been fixes at least in
the hrtimer code in this area I'm afraid that this could add new
subtle bugs.
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20101201091109.GA8984@osiris.boeblingen.de.ibm.com>
Cc: stable@kernel.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>
|
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There's a long-running regression that proved difficult to fix and
which is hitting certain people and is rather annoying in its effects.
Damien reported that after 74f5187ac8 (sched: Cure load average vs
NO_HZ woes) his load average is unnaturally high, he also noted that
even with that patch reverted the load avgerage numbers are not
correct.
The problem is that the previous patch only solved half the NO_HZ
problem, it addressed the part of going into NO_HZ mode, not of
comming out of NO_HZ mode. This patch implements that missing half.
When comming out of NO_HZ mode there are two important things to take
care of:
- Folding the pending idle delta into the global active count.
- Correctly aging the averages for the idle-duration.
So with this patch the NO_HZ interaction should be complete and
behaviour between CONFIG_NO_HZ=[yn] should be equivalent.
Furthermore, this patch slightly changes the load average computation
by adding a rounding term to the fixed point multiplication.
Reported-by: Damien Wyart <damien.wyart@free.fr>
Reported-by: Tim McGrath <tmhikaru@gmail.com>
Tested-by: Damien Wyart <damien.wyart@free.fr>
Tested-by: Orion Poplawski <orion@cora.nwra.com>
Tested-by: Kyle McMartin <kyle@mcmartin.ca>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: stable@kernel.org
Cc: Chase Douglas <chase.douglas@canonical.com>
LKML-Reference: <1291129145.32004.874.camel@laptop>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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