Messages in this thread Patch in this message | | | Date | Sat, 31 Aug 2013 01:04:49 +0200 | From | Gerlando Falauto <> | Subject | Re: kernel deadlock |
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Hi,
sorry, it took me a while to narrow it down...
On 08/30/2013 01:45 AM, John Stultz wrote: > On 08/29/2013 01:56 PM, Falauto, Gerlando wrote: >> Hi everyone, >> >> I ran into the deadlock situation reported at the bottom. >> Actually, on my latest 3.10 kernel for some reason I don't get the >> report (the kernel just hangs for some reason), so it took me quite some >> time to track it down. >> >> Once I figured the trigger to the machine hanging was adjtimex(), I >> reverted everything (between 3.9 to 3.10) that was touching >> kernel/time/timekeeping/timekeeping.c and kernel/time/ntp.c, I double >> checked that indeed the problem was not happening anymore, and finally >> started bisecting, landing on the following offending commit. >> THEN, and ONLY THEN, did I get the &%""ç+"% deadlock report. >> >> Do you guys have any ideas what could be wrong and how to fix it? > > Thanks for the report! > > What exactly is your process for reproducing the issue?
Now (well, now...), it's quite easy.
Three ingredients:
1) Kernel 3.10
2) Enable HRTICK
diff --git a/kernel/sched/features.h b/kernel/sched/features.h index 99399f8..294e3ca 100644 --- a/kernel/sched/features.h +++ b/kernel/sched/features.h @@ -41,7 +41,7 @@ SCHED_FEAT(WAKEUP_PREEMPTION, true) */ SCHED_FEAT(ARCH_POWER, true)
-SCHED_FEAT(HRTICK, false) +SCHED_FEAT(HRTICK, true) SCHED_FEAT(DOUBLE_TICK, false) SCHED_FEAT(LB_BIAS, true)
3) Run the following: #include <stdio.h> #include <sys/timex.h>
int main(void) { int i; for (i = 0 ; ; i++) { struct timex adj = {}; printf("%d\r", i); fflush(stdout); adjtimex(&adj); } return 0; } Notice how: 1) The original issue (with a bit more complicated scenario) was seen on ARM and PowerPC platforms 2) Under the above test conditions (on ARM) I *don't* get any deadlock report printed, the machine just hangs 3) The offending commit (below) I had found through a weird (manual) process of reverting and re-reverting (where some commits could have been reverted out of order), so I'm not 100% sure you'd come to the same conclusions.
commit 06c017fdd4dc48451a29ac37fc1db4a3f86b7f40 Author: John Stultz <john.stultz@linaro.org> Date: Fri Mar 22 11:37:28 2013 -0700
timekeeping: Hold timekeepering locks in do_adjtimex and hardpps
I'm not able to perform any further testing at this very moment, but if needed, I can try bisecting again sometime next week, so to make an even more reliable statement.
Thank you! Gerlando
> > >> [ INFO: inconsistent lock state ] >> 3.10.0-04864-g346ecc9-dirty #16 Not tainted >> --------------------------------- >> inconsistent {IN-HARDIRQ-W} -> {HARDIRQ-ON-W} usage. >> SAKEY/738 [HC0[0]:SC0[0]:HE1:SE1] takes: >> (timekeeper_lock){?.-...}, at: [<c004a3e4>] do_adjtimex+0x64/0xbc >> {IN-HARDIRQ-W} state was registered at: >> [<c0055138>] __lock_acquire+0xabc/0x1bb8 >> [<c0056838>] lock_acquire+0xa8/0x15c >> [<c04c14ec>] _raw_spin_lock_irqsave+0x50/0x64 >> [<c00497a4>] do_timer+0x2c/0xa54 >> [<c004e7f4>] tick_periodic+0x74/0x9c >> [<c004e834>] tick_handle_periodic+0x18/0x7c >> [<c001349c>] orion_timer_interrupt+0x24/0x34 >> [<c0069c2c>] handle_irq_event_percpu+0x5c/0x300 >> [<c0069f0c>] handle_irq_event+0x3c/0x5c >> [<c006c194>] handle_level_irq+0x8c/0xe8 >> [<c0069574>] generic_handle_irq+0x30/0x4c >> [<c000951c>] handle_IRQ+0x30/0x84 >> [<c04c2178>] __irq_svc+0x38/0xa0 >> [<c06cf15c>] calibrate_delay+0x350/0x4e4 >> [<c06986e0>] start_kernel+0x23c/0x2c4 >> [<0000803c>] 0x803c >> irq event stamp: 32358 >> hardirqs last enabled at (32357): [<c0008c64>] ret_fast_syscall+0x24/0x44 >> hardirqs last disabled at (32358): [<c04c14bc>] >> _raw_spin_lock_irqsave+0x20/0x64 >> softirqs last enabled at (32160): [<c001e234>] __do_softirq+0x1b8/0x308 >> softirqs last disabled at (32137): [<c001e77c>] irq_exit+0xa0/0xd8 >> >> other info that might help us debug this: >> Possible unsafe locking scenario: >> >> CPU0 >> ---- >> lock(timekeeper_lock); >> <Interrupt> >> lock(timekeeper_lock); >> >> *** DEADLOCK *** >> >> 1 lock held by SAKEY/738: >> #0: (timekeeper_lock){?.-...}, at: [<c004a3e4>] do_adjtimex+0x64/0xbc >> >> stack backtrace: >> CPU: 0 PID: 738 Comm: SAKEY Not tainted 3.10.0-04864-g346ecc9-dirty #16 >> [<c000d67c>] (unwind_backtrace+0x0/0xf0) from [<c000b530>] >> (show_stack+0x10/0x14) >> [<c000b530>] (show_stack+0x10/0x14) from [<c04ba07c>] >> (print_usage_bug.part.27+0x218/0x280) >> [<c04ba07c>] (print_usage_bug.part.27+0x218/0x280) from [<c0053058>] >> (mark_lock+0x538/0x6bc) >> [<c0053058>] (mark_lock+0x538/0x6bc) from [<c005326c>] >> (mark_held_locks+0x90/0x124) >> [<c005326c>] (mark_held_locks+0x90/0x124) from [<c00533a8>] >> (trace_hardirqs_on_caller+0xa8/0x23c) >> [<c00533a8>] (trace_hardirqs_on_caller+0xa8/0x23c) from [<c04c1c60>] >> (_raw_spin_unlock_irq+0x24/0x5c) >> [<c04c1c60>] (_raw_spin_unlock_irq+0x24/0x5c) from [<c004ac8c>] >> (__do_adjtimex+0x17c/0x65c) >> [<c004ac8c>] (__do_adjtimex+0x17c/0x65c) from [<c004a404>] >> (do_adjtimex+0x84/0xbc) >> [<c004a404>] (do_adjtimex+0x84/0xbc) from [<c001d62c>] >> (SyS_adjtimex+0x50/0xa8) >> [<c001d62c>] (SyS_adjtimex+0x50/0xa8) from [<c0008c40>] >> (ret_fast_syscall+0x0/0x44) > > Hrmm. So I'm a little confused by the report, as we hold the write lock > on the timekeeper_lock disabling irqs, so I'm not sure I see how the irq > could trigger to cause the deadlock. In fact, all the timekeeper_lock > users save irqs. > > Hrmm. I dunno. :( > > Thomas, you have a guess? > > Let me know how you trigger it and I'll see if I can't reproduce it myself. > > thanks > -john > > >
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