| Age | Commit message (Collapse) | Author |
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Retry loops on RT might loop forever when the modifying side was
preempted. Use cpu_chill() instead of cpu_relax() to let the system
make progress.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable-rt@vger.kernel.org
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Retry loops on RT might loop forever when the modifying side was
preempted. Use cpu_chill() instead of cpu_relax() to let the system
make progress.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable-rt@vger.kernel.org
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Retry loops on RT might loop forever when the modifying side was
preempted. Steven also observed a live lock when there was a
concurrent priority boosting going on.
Use cpu_chill() instead of cpu_relax() to let the system
make progress.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable-rt@vger.kernel.org
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We hit another bug that was caused by switching cpu_chill() from
msleep() to hrtimer_nanosleep().
This time it is a livelock. The problem is that hrtimer_nanosleep()
calls schedule with the state == TASK_INTERRUPTIBLE. But these means
that if a signal is pending, the scheduler wont schedule, and will
simply change the current task state back to TASK_RUNNING. This
nullifies the whole point of cpu_chill() in the first place. That is,
if a task is spinning on a try_lock() and it preempted the owner of the
lock, if it has a signal pending, it will never give up the CPU to let
the owner of the lock run.
I made a static function __hrtimer_nanosleep() that takes a fifth
parameter "state", which determines the task state of that the
nanosleep() will be in. The normal hrtimer_nanosleep() will act the
same, but cpu_chill() will call the __hrtimer_nanosleep() directly with
the TASK_UNINTERRUPTIBLE state.
cpu_chill() only cares that the first sleep happens, and does not care
about the state of the restart schedule (in hrtimer_nanosleep_restart).
Cc: stable-rt@vger.kernel.org
Reported-by: Ulrich Obergfell <uobergfe@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Since we replaced msleep() by hrtimer I see now and then (rarely) this:
| [....] Waiting for /dev to be fully populated...
| =====================================
| [ BUG: udevd/229 still has locks held! ]
| 3.12.11-rt17 #23 Not tainted
| -------------------------------------
| 1 lock held by udevd/229:
| #0: (&type->i_mutex_dir_key#2){+.+.+.}, at: lookup_slow+0x28/0x98
|
| stack backtrace:
| CPU: 0 PID: 229 Comm: udevd Not tainted 3.12.11-rt17 #23
| (unwind_backtrace+0x0/0xf8) from (show_stack+0x10/0x14)
| (show_stack+0x10/0x14) from (dump_stack+0x74/0xbc)
| (dump_stack+0x74/0xbc) from (do_nanosleep+0x120/0x160)
| (do_nanosleep+0x120/0x160) from (hrtimer_nanosleep+0x90/0x110)
| (hrtimer_nanosleep+0x90/0x110) from (cpu_chill+0x30/0x38)
| (cpu_chill+0x30/0x38) from (dentry_kill+0x158/0x1ec)
| (dentry_kill+0x158/0x1ec) from (dput+0x74/0x15c)
| (dput+0x74/0x15c) from (lookup_real+0x4c/0x50)
| (lookup_real+0x4c/0x50) from (__lookup_hash+0x34/0x44)
| (__lookup_hash+0x34/0x44) from (lookup_slow+0x38/0x98)
| (lookup_slow+0x38/0x98) from (path_lookupat+0x208/0x7fc)
| (path_lookupat+0x208/0x7fc) from (filename_lookup+0x20/0x60)
| (filename_lookup+0x20/0x60) from (user_path_at_empty+0x50/0x7c)
| (user_path_at_empty+0x50/0x7c) from (user_path_at+0x14/0x1c)
| (user_path_at+0x14/0x1c) from (vfs_fstatat+0x48/0x94)
| (vfs_fstatat+0x48/0x94) from (SyS_stat64+0x14/0x30)
| (SyS_stat64+0x14/0x30) from (ret_fast_syscall+0x0/0x48)
For now I see no better way but to disable the freezer the sleep the period.
Cc: stable-rt@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Ulrich Obergfell pointed out that cpu_chill() calls msleep() which is woken
up by the ksoftirqd running the TIMER softirq. But as the cpu_chill() is
called from softirq context, it may block the ksoftirqd() from running, in
which case, it may never wake up the msleep() causing the deadlock.
I checked the vmcore, and irq/74-qla2xxx is stuck in the msleep() call,
running on CPU 8. The one ksoftirqd that is stuck, happens to be the one that
runs on CPU 8, and it is blocked on a lock held by irq/74-qla2xxx. As that
ksoftirqd is the one that will wake up irq/74-qla2xxx, and it happens to be
blocked on a lock that irq/74-qla2xxx holds, we have our deadlock.
The solution is not to convert the cpu_chill() back to a cpu_relax() as that
will re-create a possible live lock that the cpu_chill() fixed earlier, and may
also leave this bug open on other softirqs. The fix is to remove the
dependency on ksoftirqd from cpu_chill(). That is, instead of calling
msleep() that requires ksoftirqd to wake it up, use the
hrtimer_nanosleep() code that does the wakeup from hard irq context.
|Looks to be the lock of the block softirq. I don't have the core dump
|anymore, but from what I could tell the ksoftirqd was blocked on the
|block softirq lock, where the block softirq handler did a msleep
|(called by the qla2xxx interrupt handler).
|
|Looking at trigger_softirq() in block/blk-softirq.c, it can do a
|smp_callfunction() to another cpu to run the block softirq. If that
|happens to be the cpu where the qla2xx irq handler is doing the block
|softirq and is in a middle of a msleep(), I believe the ksoftirqd will
|try to run the softirq. If it does that, then BOOM, it's deadlocked
|because the ksoftirqd will never run the timer softirq either.
|I should have also stated that it was only one lock that was involved.
|But the lock owner was doing a msleep() that requires a wakeup by
|ksoftirqd to continue. If ksoftirqd happens to be blocked on a lock
|held by the msleep() caller, then you have your deadlock.
|
|It's best not to have any softirqs going to sleep requiring another
|softirq to wake it up. Note, if we ever require a timer softirq to do a
|cpu_chill() it will most definitely hit this deadlock.
Cc: stable-rt@vger.kernel.org
Found-by: Ulrich Obergfell <uobergfe@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
[bigeasy: add the 4 | chapters from email]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Retry loops on RT might loop forever when the modifying side was
preempted. Add cpu_chill() to replace cpu_relax(). cpu_chill()
defaults to cpu_relax() for non RT. On RT it puts the looping task to
sleep for a tick so the preempted task can make progress.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable-rt@vger.kernel.org
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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where do I start. Let me explain what is going on here. The code
sequence
| pushf
| pop %edx
| or $0x1,%dh
| push %edx
| mov $0xe0,%eax
| popf
| sysenter
triggers the bug. On 64bit kernel we see the double fault (with 32bit and
64bit userland) and on 32bit kernel there is no problem. The reporter said
that double fault does not happen on 64bit kernel with 64bit userland and
this is because in that case the VDSO uses the "syscall" interface instead
of "sysenter".
The bug. "popf" loads the flags with the TF bit set which enables
"single stepping" and this leads to a debug exception. Usually on 64bit
we have a special IST stack for the debug exception. Due to patch [0] we
do not use the IST stack but the kernel stack instead. On 64bit the
sysenter instruction starts in kernel with the stack address NULL. The
code sequence above enters the debug exception (TF flag) after the
sysenter instruction was executed which sets the stack pointer to NULL
and we have a fault (it seems that the debug exception saves some bytes
on the stack).
To fix the double fault I'm going to drop patch [0]. It is completely
pointless. In do_debug() and do_stack_segment() we disable preemption
which means the task can't leave the CPU. So it does not matter if we run
on IST or on kernel stack.
There is a patch [1] which drops preempt_disable() call for a 32bit
kernel but not for 64bit so there should be no regression.
And [1] seems valid even for this code sequence. We enter the debug
exception with a 256bytes long per cpu stack and migrate to the kernel
stack before calling do_debug().
[0] x86-disable-debug-stack.patch
[1] fix-rt-int3-x86_32-3.2-rt.patch
Cc: stable-rt@vger.kernel.org
Reported-by: Brian Silverman <bsilver16384@gmail.com>
Cc: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Normally the x86-64 trap handlers for debug/int 3/stack fault run
on a special interrupt stack to make them more robust
when dealing with kernel code.
The PREEMPT_RT kernel can sleep in locks even while allocating
GFP_ATOMIC memory. When one of these trap handlers needs to send
real time signals for ptrace it allocates memory and could then
try to to schedule. But it is not allowed to schedule on a
IST stack. This can cause warnings and hangs.
This patch disables the IST stacks for these handlers for PREEMPT_RT
kernel. Instead let them run on the normal process stack.
The kernel only really needs the ISTs here to make kernel debuggers more
robust in case someone sets a break point somewhere where the stack is
invalid. But there are no kernel debuggers in the standard kernel
that do this.
It also means kprobes cannot be set in situations with invalid stack;
but that sounds like a reasonable restriction.
The stack fault change could minimally impact oops quality, but not very
much because stack faults are fairly rare.
A better solution would be to use similar logic as the NMI "paranoid"
path: check if signal is for user space, if yes go back to entry.S, switch stack,
call sync_regs, then do the signal sending etc.
But this patch is much simpler and should work too with minimal impact.
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Simplifies the separation of anon_rw_semaphores and rw_semaphores for
-rt.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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CPU bringup calls into the random pool to initialize the stack
canary. During boot that works nicely even on RT as the might sleep
checks are disabled. During CPU hotplug the might sleep checks
trigger. Making the locks in random raw is a major PITA, so avoid the
call on RT is the only sensible solution. This is basically the same
randomness which we get during boot where the random pool has no
entropy and we rely on the TSC randomnness.
Reported-by: Carsten Emde <carsten.emde@osadl.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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We had a customer report a lockup on a 3.0-rt kernel that had the
following backtrace:
[ffff88107fca3e80] rt_spin_lock_slowlock at ffffffff81499113
[ffff88107fca3f40] rt_spin_lock at ffffffff81499a56
[ffff88107fca3f50] __wake_up at ffffffff81043379
[ffff88107fca3f80] mce_notify_irq at ffffffff81017328
[ffff88107fca3f90] intel_threshold_interrupt at ffffffff81019508
[ffff88107fca3fa0] smp_threshold_interrupt at ffffffff81019fc1
[ffff88107fca3fb0] threshold_interrupt at ffffffff814a1853
It actually bugged because the lock was taken by the same owner that
already had that lock. What happened was the thread that was setting
itself on a wait queue had the lock when an MCE triggered. The MCE
interrupt does a wake up on its wait list and grabs the same lock.
NOTE: THIS IS NOT A BUG ON MAINLINE
Sorry for yelling, but as I Cc'd mainline maintainers I want them to
know that this is an PREEMPT_RT bug only. I only Cc'd them for advice.
On PREEMPT_RT the wait queue locks are converted from normal
"spin_locks" into an rt_mutex (see the rt_spin_lock_slowlock above).
These are not to be taken by hard interrupt context. This usually isn't
a problem as most all interrupts in PREEMPT_RT are converted into
schedulable threads. Unfortunately that's not the case with the MCE irq.
As wait queue locks are notorious for long hold times, we can not
convert them to raw_spin_locks without causing issues with -rt. But
Thomas has created a "simple-wait" structure that uses raw spin locks
which may have been a good fit.
Unfortunately, wait queues are not the only issue, as the mce_notify_irq
also does a schedule_work(), which grabs the workqueue spin locks that
have the exact same issue.
Thus, this patch I'm proposing is to move the actual work of the MCE
interrupt into a helper thread that gets woken up on the MCE interrupt
and does the work in a schedulable context.
NOTE: THIS PATCH ONLY CHANGES THE BEHAVIOR WHEN PREEMPT_RT IS SET
Oops, sorry for yelling again, but I want to stress that I keep the same
behavior of mainline when PREEMPT_RT is not set. Thus, this only changes
the MCE behavior when PREEMPT_RT is configured.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
[bigeasy@linutronix: make mce_notify_work() a proper prototype, use
kthread_run()]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Seems mce timer fire at the wrong frequency in -rt kernels since roughly
forever due to 32 bit overflow. 3.8-rt is also missing a multiplier.
Add missing us -> ns conversion and 32 bit overflow prevention.
Cc: stable-rt@vger.kernel.org
Signed-off-by: Mike Galbraith <bitbucket@online.de>
[bigeasy: use ULL instead of u64 cast]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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mce_timer is started in atomic contexts of cpu bringup. This results
in might_sleep() warnings on RT. Convert mce_timer to a hrtimer to
avoid this.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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One of the requirements is that the lock has to fit in an u32 which does
not work with the sleeping locks. We would have to use the bare raw
locks for this and I would like to avoid this.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Two cps in parallel managed to stall the the ext4 fs. It seems that
journal code is either waiting for locks or sleeping waiting for
something to happen. This seems similar to what Mike observed on ext3,
here is his description:
|With an -rt kernel, and a heavy sync IO load, tasks can jam
|up on journal locks without unplugging, which can lead to
|terminal IO starvation. Unplug and schedule when waiting
|for space.
Cc: stable-rt@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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|
With an -rt kernel, and a heavy sync IO load, tasks can jam
up on journal locks without unplugging, which can lead to
terminal IO starvation. Unplug and schedule when waiting for space.
Signed-off-by: Mike Galbraith <mgalbraith@suse.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Theodore Tso <tytso@mit.edu>
Link: http://lkml.kernel.org/r/1341812414.7370.73.camel@marge.simpson.net
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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On Sat, 2007-10-27 at 11:44 +0200, Ingo Molnar wrote:
> * Nick Piggin <nickpiggin@yahoo.com.au> wrote:
>
> > > [10138.175796] [<c0105de3>] show_trace+0x12/0x14
> > > [10138.180291] [<c0105dfb>] dump_stack+0x16/0x18
> > > [10138.184769] [<c011609f>] native_smp_call_function_mask+0x138/0x13d
> > > [10138.191117] [<c0117606>] smp_call_function+0x1e/0x24
> > > [10138.196210] [<c012f85c>] on_each_cpu+0x25/0x50
> > > [10138.200807] [<c0115c74>] flush_tlb_all+0x1e/0x20
> > > [10138.205553] [<c016caaf>] kmap_high+0x1b6/0x417
> > > [10138.210118] [<c011ec88>] kmap+0x4d/0x4f
> > > [10138.214102] [<c026a9d8>] ntfs_end_buffer_async_read+0x228/0x2f9
> > > [10138.220163] [<c01a0e9e>] end_bio_bh_io_sync+0x26/0x3f
> > > [10138.225352] [<c01a2b09>] bio_endio+0x42/0x6d
> > > [10138.229769] [<c02c2a08>] __end_that_request_first+0x115/0x4ac
> > > [10138.235682] [<c02c2da7>] end_that_request_chunk+0x8/0xa
> > > [10138.241052] [<c0365943>] ide_end_request+0x55/0x10a
> > > [10138.246058] [<c036dae3>] ide_dma_intr+0x6f/0xac
> > > [10138.250727] [<c0366d83>] ide_intr+0x93/0x1e0
> > > [10138.255125] [<c015afb4>] handle_IRQ_event+0x5c/0xc9
> >
> > Looks like ntfs is kmap()ing from interrupt context. Should be using
> > kmap_atomic instead, I think.
>
> it's not atomic interrupt context but irq thread context - and -rt
> remaps kmap_atomic() to kmap() internally.
Hm. Looking at the change to mm/bounce.c, perhaps I should do this
instead?
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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User preempt_*_rt instead of local_irq_*_rt or otherwise there will be
warning on ARM like below:
WARNING: at build/linux/kernel/smp.c:459 smp_call_function_many+0x98/0x264()
Modules linked in:
[<c0013bb4>] (unwind_backtrace+0x0/0xe4) from [<c001be94>] (warn_slowpath_common+0x4c/0x64)
[<c001be94>] (warn_slowpath_common+0x4c/0x64) from [<c001bec4>] (warn_slowpath_null+0x18/0x1c)
[<c001bec4>] (warn_slowpath_null+0x18/0x1c) from [<c0053ff8>](smp_call_function_many+0x98/0x264)
[<c0053ff8>] (smp_call_function_many+0x98/0x264) from [<c0054364>] (smp_call_function+0x44/0x6c)
[<c0054364>] (smp_call_function+0x44/0x6c) from [<c0017d50>] (__new_context+0xbc/0x124)
[<c0017d50>] (__new_context+0xbc/0x124) from [<c009e49c>] (flush_old_exec+0x460/0x5e4)
[<c009e49c>] (flush_old_exec+0x460/0x5e4) from [<c00d61ac>] (load_elf_binary+0x2e0/0x11ac)
[<c00d61ac>] (load_elf_binary+0x2e0/0x11ac) from [<c009d060>] (search_binary_handler+0x94/0x2a4)
[<c009d060>] (search_binary_handler+0x94/0x2a4) from [<c009e8fc>] (do_execve+0x254/0x364)
[<c009e8fc>] (do_execve+0x254/0x364) from [<c0010e84>] (sys_execve+0x34/0x54)
[<c0010e84>] (sys_execve+0x34/0x54) from [<c000da00>] (ret_fast_syscall+0x0/0x30)
---[ end trace 0000000000000002 ]---
The reason is that ARM need irq enabled when doing activate_mm().
According to mm-protect-activate-switch-mm.patch, actually
preempt_[disable|enable]_rt() is sufficient.
Inspired-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Yong Zhang <yong.zhang0@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/1337061236-1766-1-git-send-email-yong.zhang0@gmail.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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On RT we cannot loop with preemption disabled here as
mnt_make_readonly() might have been preempted. We can safely enable
preemption while waiting for MNT_WRITE_HOLD to be cleared. Safe on !RT
as well.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Beyond the warning:
drivers/tty/serial/8250/8250.c:1613:6: warning: unused variable ‘pass_counter’ [-Wunused-variable]
the solution of just looping infinitely was ugly - up it to 1 million to
give it a chance to continue in some really ugly situation.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Signed-off-by: Ingo Molnar <mingo@elte.hu>
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Signed-off-by: David S. Miller <davem@davemloft.net>
Tested-by: Allen Pais <allen.pais@oracle.com>
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In -RT the spin_lock_irqsave() does not spin but sleep if the lock is
taken. Before that, local_irq_save() is invoked which disables
interrupts even on -RT. Therefore local_irq_save() + spin_lock() does not
work.
In the ->sysrq and oops_in_progress case it is save to trylock the lock
i.e. this is what we do now anyway except for ->sysrq where we assume
that the lock is already taken.
The spin_lock_irqsave() grabs the lock and disables the interrupts on
vanilla (the same behavior) and on -RT it won't disable interrupts.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
[bigeasy: add a patch description]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Any callers to the function rcu_preempt_qs() must disable irqs in
order to protect the assignment to ->rcu_read_unlock_special. In
RT case, rcu_bh_qs() as the wrapper of rcu_preempt_qs() is called
in some scenarios where irq is enabled, like this path,
do_single_softirq()
|
+ local_irq_enable();
+ handle_softirq()
| |
| + rcu_bh_qs()
| |
| + rcu_preempt_qs()
|
+ local_irq_disable()
So here we'd better disable irq directly inside of rcu_bh_qs() to
fix this, otherwise the kernel may be freezable sometimes as
observed. And especially this way is also kind and safe for the
potential rcu_bh_qs() usage elsewhere in the future.
Cc: stable-rt@vger.kernel.org
Signed-off-by: Tiejun Chen <tiejun.chen@windriver.com>
Signed-off-by: Bin Jiang <bin.jiang@windriver.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Implementing RCU-bh in terms of RCU-preempt makes the system vulnerable
to network-based denial-of-service attacks. This patch therefore
makes __do_softirq() invoke rcu_bh_qs(), but only when __do_softirq()
is running in ksoftirqd context. A wrapper layer in interposed so that
other calls to __do_softirq() avoid invoking rcu_bh_qs(). The underlying
function __do_softirq_common() does the actual work.
The reason that rcu_bh_qs() is bad in these non-ksoftirqd contexts is
that there might be a local_bh_enable() inside an RCU-preempt read-side
critical section. This local_bh_enable() can invoke __do_softirq()
directly, so if __do_softirq() were to invoke rcu_bh_qs() (which just
calls rcu_preempt_qs() in the PREEMPT_RT_FULL case), there would be
an illegal RCU-preempt quiescent state in the middle of an RCU-preempt
read-side critical section. Therefore, quiescent states can only happen
in cases where __do_softirq() is invoked directly from ksoftirqd.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/20111005184518.GA21601@linux.vnet.ibm.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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The Linux kernel has long RCU-bh read-side critical sections that
intolerably increase scheduling latency under mainline's RCU-bh rules,
which include RCU-bh read-side critical sections being non-preemptible.
This patch therefore arranges for RCU-bh to be implemented in terms of
RCU-preempt for CONFIG_PREEMPT_RT_FULL=y.
This has the downside of defeating the purpose of RCU-bh, namely,
handling the case where the system is subjected to a network-based
denial-of-service attack that keeps at least one CPU doing full-time
softirq processing. This issue will be fixed by a later commit.
The current commit will need some work to make it appropriate for
mainline use, for example, it needs to be extended to cover Tiny RCU.
[ paulmck: Added a useful changelog ]
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/20111005185938.GA20403@linux.vnet.ibm.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
|
|
With RT_FULL we get the below wreckage:
[ 126.060484] =======================================================
[ 126.060486] [ INFO: possible circular locking dependency detected ]
[ 126.060489] 3.0.1-rt10+ #30
[ 126.060490] -------------------------------------------------------
[ 126.060492] irq/24-eth0/1235 is trying to acquire lock:
[ 126.060495] (&(lock)->wait_lock#2){+.+...}, at: [<ffffffff81501c81>] rt_mutex_slowunlock+0x16/0x55
[ 126.060503]
[ 126.060504] but task is already holding lock:
[ 126.060506] (&p->pi_lock){-...-.}, at: [<ffffffff81074fdc>] try_to_wake_up+0x35/0x429
[ 126.060511]
[ 126.060511] which lock already depends on the new lock.
[ 126.060513]
[ 126.060514]
[ 126.060514] the existing dependency chain (in reverse order) is:
[ 126.060516]
[ 126.060516] -> #1 (&p->pi_lock){-...-.}:
[ 126.060519] [<ffffffff810afe9e>] lock_acquire+0x145/0x18a
[ 126.060524] [<ffffffff8150291e>] _raw_spin_lock_irqsave+0x4b/0x85
[ 126.060527] [<ffffffff810b5aa4>] task_blocks_on_rt_mutex+0x36/0x20f
[ 126.060531] [<ffffffff815019bb>] rt_mutex_slowlock+0xd1/0x15a
[ 126.060534] [<ffffffff81501ae3>] rt_mutex_lock+0x2d/0x2f
[ 126.060537] [<ffffffff810d9020>] rcu_boost+0xad/0xde
[ 126.060541] [<ffffffff810d90ce>] rcu_boost_kthread+0x7d/0x9b
[ 126.060544] [<ffffffff8109a760>] kthread+0x99/0xa1
[ 126.060547] [<ffffffff81509b14>] kernel_thread_helper+0x4/0x10
[ 126.060551]
[ 126.060552] -> #0 (&(lock)->wait_lock#2){+.+...}:
[ 126.060555] [<ffffffff810af1b8>] __lock_acquire+0x1157/0x1816
[ 126.060558] [<ffffffff810afe9e>] lock_acquire+0x145/0x18a
[ 126.060561] [<ffffffff8150279e>] _raw_spin_lock+0x40/0x73
[ 126.060564] [<ffffffff81501c81>] rt_mutex_slowunlock+0x16/0x55
[ 126.060566] [<ffffffff81501ce7>] rt_mutex_unlock+0x27/0x29
[ 126.060569] [<ffffffff810d9f86>] rcu_read_unlock_special+0x17e/0x1c4
[ 126.060573] [<ffffffff810da014>] __rcu_read_unlock+0x48/0x89
[ 126.060576] [<ffffffff8106847a>] select_task_rq_rt+0xc7/0xd5
[ 126.060580] [<ffffffff8107511c>] try_to_wake_up+0x175/0x429
[ 126.060583] [<ffffffff81075425>] wake_up_process+0x15/0x17
[ 126.060585] [<ffffffff81080a51>] wakeup_softirqd+0x24/0x26
[ 126.060590] [<ffffffff81081df9>] irq_exit+0x49/0x55
[ 126.060593] [<ffffffff8150a3bd>] smp_apic_timer_interrupt+0x8a/0x98
[ 126.060597] [<ffffffff81509793>] apic_timer_interrupt+0x13/0x20
[ 126.060600] [<ffffffff810d5952>] irq_forced_thread_fn+0x1b/0x44
[ 126.060603] [<ffffffff810d582c>] irq_thread+0xde/0x1af
[ 126.060606] [<ffffffff8109a760>] kthread+0x99/0xa1
[ 126.060608] [<ffffffff81509b14>] kernel_thread_helper+0x4/0x10
[ 126.060611]
[ 126.060612] other info that might help us debug this:
[ 126.060614]
[ 126.060615] Possible unsafe locking scenario:
[ 126.060616]
[ 126.060617] CPU0 CPU1
[ 126.060619] ---- ----
[ 126.060620] lock(&p->pi_lock);
[ 126.060623] lock(&(lock)->wait_lock);
[ 126.060625] lock(&p->pi_lock);
[ 126.060627] lock(&(lock)->wait_lock);
[ 126.060629]
[ 126.060629] *** DEADLOCK ***
[ 126.060630]
[ 126.060632] 1 lock held by irq/24-eth0/1235:
[ 126.060633] #0: (&p->pi_lock){-...-.}, at: [<ffffffff81074fdc>] try_to_wake_up+0x35/0x429
[ 126.060638]
[ 126.060638] stack backtrace:
[ 126.060641] Pid: 1235, comm: irq/24-eth0 Not tainted 3.0.1-rt10+ #30
[ 126.060643] Call Trace:
[ 126.060644] <IRQ> [<ffffffff810acbde>] print_circular_bug+0x289/0x29a
[ 126.060651] [<ffffffff810af1b8>] __lock_acquire+0x1157/0x1816
[ 126.060655] [<ffffffff810ab3aa>] ? trace_hardirqs_off_caller+0x1f/0x99
[ 126.060658] [<ffffffff81501c81>] ? rt_mutex_slowunlock+0x16/0x55
[ 126.060661] [<ffffffff810afe9e>] lock_acquire+0x145/0x18a
[ 126.060664] [<ffffffff81501c81>] ? rt_mutex_slowunlock+0x16/0x55
[ 126.060668] [<ffffffff8150279e>] _raw_spin_lock+0x40/0x73
[ 126.060671] [<ffffffff81501c81>] ? rt_mutex_slowunlock+0x16/0x55
[ 126.060674] [<ffffffff810d9655>] ? rcu_report_qs_rsp+0x87/0x8c
[ 126.060677] [<ffffffff81501c81>] rt_mutex_slowunlock+0x16/0x55
[ 126.060680] [<ffffffff810d9ea3>] ? rcu_read_unlock_special+0x9b/0x1c4
[ 126.060683] [<ffffffff81501ce7>] rt_mutex_unlock+0x27/0x29
[ 126.060687] [<ffffffff810d9f86>] rcu_read_unlock_special+0x17e/0x1c4
[ 126.060690] [<ffffffff810da014>] __rcu_read_unlock+0x48/0x89
[ 126.060693] [<ffffffff8106847a>] select_task_rq_rt+0xc7/0xd5
[ 126.060696] [<ffffffff810683da>] ? select_task_rq_rt+0x27/0xd5
[ 126.060701] [<ffffffff810a852a>] ? clockevents_program_event+0x8e/0x90
[ 126.060704] [<ffffffff8107511c>] try_to_wake_up+0x175/0x429
[ 126.060708] [<ffffffff810a95dc>] ? tick_program_event+0x1f/0x21
[ 126.060711] [<ffffffff81075425>] wake_up_process+0x15/0x17
[ 126.060715] [<ffffffff81080a51>] wakeup_softirqd+0x24/0x26
[ 126.060718] [<ffffffff81081df9>] irq_exit+0x49/0x55
[ 126.060721] [<ffffffff8150a3bd>] smp_apic_timer_interrupt+0x8a/0x98
[ 126.060724] [<ffffffff81509793>] apic_timer_interrupt+0x13/0x20
[ 126.060726] <EOI> [<ffffffff81072855>] ? migrate_disable+0x75/0x12d
[ 126.060733] [<ffffffff81080a61>] ? local_bh_disable+0xe/0x1f
[ 126.060736] [<ffffffff81080a70>] ? local_bh_disable+0x1d/0x1f
[ 126.060739] [<ffffffff810d5952>] irq_forced_thread_fn+0x1b/0x44
[ 126.060742] [<ffffffff81502ac0>] ? _raw_spin_unlock_irq+0x3b/0x59
[ 126.060745] [<ffffffff810d582c>] irq_thread+0xde/0x1af
[ 126.060748] [<ffffffff810d5937>] ? irq_thread_fn+0x3a/0x3a
[ 126.060751] [<ffffffff810d574e>] ? irq_finalize_oneshot+0xd1/0xd1
[ 126.060754] [<ffffffff810d574e>] ? irq_finalize_oneshot+0xd1/0xd1
[ 126.060757] [<ffffffff8109a760>] kthread+0x99/0xa1
[ 126.060761] [<ffffffff81509b14>] kernel_thread_helper+0x4/0x10
[ 126.060764] [<ffffffff81069ed7>] ? finish_task_switch+0x87/0x10a
[ 126.060768] [<ffffffff81502ec4>] ? retint_restore_args+0xe/0xe
[ 126.060771] [<ffffffff8109a6c7>] ? __init_kthread_worker+0x8c/0x8c
[ 126.060774] [<ffffffff81509b10>] ? gs_change+0xb/0xb
Because irq_exit() does:
void irq_exit(void)
{
account_system_vtime(current);
trace_hardirq_exit();
sub_preempt_count(IRQ_EXIT_OFFSET);
if (!in_interrupt() && local_softirq_pending())
invoke_softirq();
...
}
Which triggers a wakeup, which uses RCU, now if the interrupted task has
t->rcu_read_unlock_special set, the rcu usage from the wakeup will end
up in rcu_read_unlock_special(). rcu_read_unlock_special() will test
for in_irq(), which will fail as we just decremented preempt_count
with IRQ_EXIT_OFFSET, and in_sering_softirq(), which for
PREEMPT_RT_FULL reads:
int in_serving_softirq(void)
{
int res;
preempt_disable();
res = __get_cpu_var(local_softirq_runner) == current;
preempt_enable();
return res;
}
Which will thus also fail, resulting in the above wreckage.
The 'somewhat' ugly solution is to open-code the preempt_count() test
in rcu_read_unlock_special().
Also, we're not at all sure how ->rcu_read_unlock_special gets set
here... so this is very likely a bandaid and more thought is required.
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
|
|
Mike Galbraith captered the following:
| >#11 [ffff88017b243e90] _raw_spin_lock at ffffffff815d2596
| >#12 [ffff88017b243e90] rt_mutex_trylock at ffffffff815d15be
| >#13 [ffff88017b243eb0] get_next_timer_interrupt at ffffffff81063b42
| >#14 [ffff88017b243f00] tick_nohz_stop_sched_tick at ffffffff810bd1fd
| >#15 [ffff88017b243f70] tick_nohz_irq_exit at ffffffff810bd7d2
| >#16 [ffff88017b243f90] irq_exit at ffffffff8105b02d
| >#17 [ffff88017b243fb0] reschedule_interrupt at ffffffff815db3dd
| >--- <IRQ stack> ---
| >#18 [ffff88017a2a9bc8] reschedule_interrupt at ffffffff815db3dd
| > [exception RIP: task_blocks_on_rt_mutex+51]
| >#19 [ffff88017a2a9ce0] rt_spin_lock_slowlock at ffffffff815d183c
| >#20 [ffff88017a2a9da0] lock_timer_base.isra.35 at ffffffff81061cbf
| >#21 [ffff88017a2a9dd0] schedule_timeout at ffffffff815cf1ce
| >#22 [ffff88017a2a9e50] rcu_gp_kthread at ffffffff810f9bbb
| >#23 [ffff88017a2a9ed0] kthread at ffffffff810796d5
| >#24 [ffff88017a2a9f50] ret_from_fork at ffffffff815da04c
lock_timer_base() does a try_lock() which deadlocks on the waiter lock
not the lock itself.
This patch takes the waiter_lock with trylock so it should work from interrupt
context as well. If the fastpath doesn't work and the waiter_lock itself is
taken then it seems that the lock itself taken.
This patch also adds "rt_spin_unlock_after_trylock_in_irq" to keep lockdep
happy. If we managed to take the wait_lock in the first place we should also
be able to take it in the unlock path.
Cc: stable-rt@vger.kernel.org
Reported-by: Mike Galbraith <bitbucket@online.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
It was previously discovered that some systems would hang on boot up
with a previous version of 3.12-rt. This was due to RCU using irq_work,
and RT defers the irq_work to a softirq. But if there's no active
timers, the softirq will not be raised, and RCU work will not get done,
causing the system to hang. The fix was to check that if there was no
active timers but irq_work to be done, then we should raise the softirq.
But this fix was not 100% correct. It left out the case that there were
active timers that were not expired yet. This would have the softirq
not get raised even if there was irq work to be done.
If there is irq_work to be done, then we must raise the timer softirq
regardless of if there is active timers or whether they are expired or
not. The softirq can handle those cases. But we can never ignore
irq_work.
As it is only PREEMPT_RT_FULL that requires irq_work to be done in the
softirq, we can pull out the check in the active_timers condition, and
make the code a bit cleaner by having the irq_work check separate, and
put the code in with the other #ifdef PREEMPT_RT. If there is irq_work
to be done, there's no need to check the active timers or if they are
expired. Just raise the time softirq and be done with it. Otherwise, we
can do the timer checks just like we do with non -rt.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
[ Talking with Sebastian on IRC, it seems that doing the irq_work_run()
from the interrupt in -rt is a bad thing. Here we simply raise the
softirq if there's irq work to do. This too boots on my i7 ]
After trying hard to figure out why my i7 box was locking up with the
new active_timers code, that does not run the timer softirq if there
are no active timers, I took an extra look at the softirq handler and
noticed that it doesn't just run timer softirqs, it also runs irq work.
This was the bug that was locking up the system. It wasn't missing a
timer, it was missing irq work. By always doing the irq work callbacks,
the system boots fine. The missing irq work callback was the RCU's
sp_wakeup() function.
No need to check for defined(CONFIG_IRQ_WORK). When that's not set the
"irq_work_needs_cpu()" is a static inline that returns false.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
Mike,
On Thu, 7 Nov 2013, Mike Galbraith wrote:
> On Thu, 2013-11-07 at 04:26 +0100, Mike Galbraith wrote:
> > On Wed, 2013-11-06 at 18:49 +0100, Thomas Gleixner wrote:
>
> > > I bet you are trying to work around some of the side effects of the
> > > occasional tick which is still necessary despite of full nohz, right?
> >
> > Nope, I wanted to check out cost of nohz_full for rt, and found that it
> > doesn't work at all instead, looked, and found that the sole running
> > task has just awakened ksoftirqd when it wants to shut the tick down, so
> > that shutdown never happens.
>
> Like so in virgin 3.10-rt. Box is x3550 M3 booted nowatchdog
> rcu_nocbs=1-3 nohz_full=1-3, and CPUs1-3 are completely isolated via
> cpusets as well.
well, that very same problem is in mainline if you add "threadirqs" to
the command line. But we can be smart about this. The untested patch
below should address that issue. If that works on mainline we can
adapt it for RT (needs a trylock(&base->lock) there).
Though it's not a full solution. It needs some thought versus the
softirq code of timers. Assume we have only one timer queued 1000
ticks into the future. So this change will cause the timer softirq not
to be called until that timer expires and then the timer softirq is
going to do 1000 loops until it catches up with jiffies. That's
anything but pretty ...
What worries me more is this one:
pert-5229 [003] d..h1.. 684.482618: softirq_raise: vec=9 [action=RCU]
The CPU has no callbacks as you shoved them over to cpu 0, so why is
the RCU softirq raised?
Thanks,
tglx
------------------
Message-id: <alpine.DEB.2.02.1311071158350.23353@ionos.tec.linutronix.de>
|CONFIG_NO_HZ_FULL + CONFIG_PREEMPT_RT_FULL = nogo
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
|
|
This fixes the following build error for the preempt-rt kernel.
make kernel/fork.o
CC kernel/fork.o
kernel/fork.c:90: error: section of tasklist_lock conflicts with previous declaration
make[2]: *** [kernel/fork.o] Error 1
make[1]: *** [kernel/fork.o] Error 2
The rt kernel cache aligns the RWLOCK in DEFINE_RWLOCK by default.
The non-rt kernels explicitly cache align only the tasklist_lock in
kernel/fork.c
That can create a build conflict. This fixes the build problem by making the
non-rt kernels cache align RWLOCKs by default. The side effect is that
the other RWLOCKs are also cache aligned for non-rt.
This is a short term solution for rt only.
The longer term solution would be to push the cache aligned DEFINE_RWLOCK
to mainline. If there are objections, then we could create a
DEFINE_RWLOCK_CACHE_ALIGNED or something of that nature.
Comments? Objections?
Signed-off-by: John Kacur <jkacur@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/alpine.LFD.2.00.1109191104010.23118@localhost6.localdomain6
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
|
|
Bad return value in _mutex_lock_check_stamp - this problem only would show
up with 3.12.1 rt4 applied but CONFIG_PREEMPT_RT_FULL not enabled
currently it would be returning what ever vprintk_emit ended up with
(atleast on x86), which probably is not the intended behavior. Added a
return 0; as in the case with CONFIG_PREEMPT_RT_FULL enabled.
Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
lockdep says:
| --------------------------------------------------------------------------
| | Wound/wait tests |
| ---------------------
| ww api failures: ok | ok | ok |
| ww contexts mixing: ok | ok |
| finishing ww context: ok | ok | ok | ok |
| locking mismatches: ok | ok | ok |
| EDEADLK handling: ok | ok | ok | ok | ok | ok | ok | ok | ok | ok |
| spinlock nest unlocked: ok |
| -----------------------------------------------------
| |block | try |context|
| -----------------------------------------------------
| context: ok | ok | ok |
| try: ok | ok | ok |
| block: ok | ok | ok |
| spinlock: ok | ok | ok |
Signed-off-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
|
|
The shortcut on mainline skip lockdep. No idea why this is a good thing.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
With the migration pushdonw a few of the do{ }while(0)
loops became obsolete but got left over - this patch
only removes this fallout.
Patch applies on top of 3.12.9-rt13
Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
pushdown of migrate_disable/enable from read_*lock* to the rt_read_*lock*
api level
general mapping to mutexes:
read_*lock*
`-> rt_read_*lock*
`-> __spin_lock (the sleeping spin locks)
`-> rt_mutex
The real read_lock* mapping:
read_lock_irqsave -.
read_lock_irq `-> rt_read_lock_irqsave()
`->read_lock ---------. \
read_lock_bh ------+ \
`--> rt_read_lock()
if (rt_mutex_owner(lock) != current){
`-> __rt_spin_lock()
rt_spin_lock_fastlock()
`->rt_mutex_cmpxchg()
migrate_disable()
}
rwlock->read_depth++;
read_trylock mapping:
read_trylock
`-> rt_read_trylock
if (rt_mutex_owner(lock) != current){
`-> rt_mutex_trylock()
rt_mutex_fasttrylock()
rt_mutex_cmpxchg()
migrate_disable()
}
rwlock->read_depth++;
read_unlock* mapping:
read_unlock_bh --------+
read_unlock_irq -------+
read_unlock_irqrestore +
read_unlock -----------+
`-> rt_read_unlock()
if(--rwlock->read_depth==0){
`-> __rt_spin_unlock()
rt_spin_lock_fastunlock()
`-> rt_mutex_cmpxchg()
migrate_disable()
}
So calls to migrate_disable/enable() are better placed at the rt_read_*
level of lock/trylock/unlock as all of the read_*lock* API has this as a
common path. In the rt_read* API of lock/trylock/unlock the nesting level
is already being recorded in rwlock->read_depth, so we can push down the
migrate disable/enable to that level and condition it on the read_depth
going from 0 to 1 -> migrate_disable and 1 to 0 -> migrate_enable. This
eliminates the recursive calls that were needed when migrate_disable/enable
was done at the read_*lock* level.
The approach to read_*_bh also eliminates the concerns raised with the
regards to api inbalances (read_lock_bh -> read_unlock+local_bh_enable)
Tested-by: Carsten Emde <C.Emde@osadl.org>
Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
pushdown of migrate_disable/enable from write_*lock* to the rt_write_*lock*
api level
general mapping of write_*lock* to mutexes:
write_*lock*
`-> rt_write_*lock*
`-> __spin_lock (the sleeping __spin_lock)
`-> rt_mutex
write_*lock*s are non-recursive so we have two lock chains to consider
- write_trylock*/write_unlock
- write_lock*/wirte_unlock
for both paths the migration_disable/enable must be balanced.
write_trylock* mapping:
write_trylock_irqsave
`-> rt_write_trylock_irqsave
write_trylock \
`--------> rt_write_trylock
ret = rt_mutex_trylock
rt_mutex_fasttrylock
rt_mutex_cmpxchg
if (ret)
migrate_disable
write_lock* mapping:
write_lock_irqsave
`-> rt_write_lock_irqsave
write_lock_irq -> write_lock ----. \
write_lock_bh -+ \
`-> rt_write_lock
__rt_spin_lock()
rt_spin_lock_fastlock()
rt_mutex_cmpxchg()
migrate_disable()
write_unlock* mapping:
write_unlock_irqrestore.
write_unlock_bh -------+
write_unlock_irq -> write_unlock ----------+
`-> rt_write_unlock()
__rt_spin_unlock()
rt_spin_lock_fastunlock()
rt_mutex_cmpxchg()
migrate_enable()
So calls to migrate_disable/enable() are better placed at the rt_write_*
level of lock/trylock/unlock as all of the write_*lock* API has this as a
common path.
This approach to write_*_bh also eliminates the concerns raised with
regards to api inbalances (write_lock_bh -> write_unlock+local_bh_enable)
Tested-by: Carsten Emde <C.Emde@osadl.org>
Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
