Messages in this thread Patch in this message | | | Date | Fri, 14 Sep 2012 11:02:31 +0800 | From | Michael Wang <> | Subject | Re: [PATCH] sched: unify the check on atomic sleeping in __might_sleep() and schedule_bug() |
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On 09/13/2012 06:04 PM, Peter Zijlstra wrote: > On Wed, 2012-08-22 at 10:40 +0800, Michael Wang wrote: >> From: Michael Wang <wangyun@linux.vnet.ibm.com> >> >> Fengguang Wu <wfg@linux.intel.com> has reported the bug: >> >> [ 0.043953] BUG: scheduling while atomic: swapper/0/1/0x10000002 >> [ 0.044017] no locks held by swapper/0/1. >> [ 0.044692] Pid: 1, comm: swapper/0 Not tainted 3.6.0-rc1-00420-gb7aebb9 #34 >> [ 0.045861] Call Trace: >> [ 0.048071] [<c106361e>] __schedule_bug+0x5e/0x70 >> [ 0.048890] [<c1b28701>] __schedule+0x91/0xb10 >> [ 0.049660] [<c14472ea>] ? vsnprintf+0x33a/0x450 >> [ 0.050444] [<c1060006>] ? lg_local_lock+0x6/0x70 >> [ 0.051256] [<c14fb5b1>] ? wait_for_xmitr+0x31/0x90 >> [ 0.052019] [<c144fd55>] ? do_raw_spin_unlock+0xa5/0xf0 >> [ 0.052903] [<c1b2a532>] ? _raw_spin_unlock+0x22/0x30 >> [ 0.053759] [<c105cdbb>] ? up+0x1b/0x70 >> [ 0.054421] [<c1065d6b>] __cond_resched+0x1b/0x30 >> [ 0.055228] [<c1b292d5>] _cond_resched+0x45/0x50 >> [ 0.056020] [<c1b26c58>] mutex_lock_nested+0x28/0x370 >> [ 0.056884] [<c1034222>] ? console_unlock+0x3a2/0x4e0 >> [ 0.057741] [<c1ac8559>] __irq_alloc_descs+0x39/0x1c0 >> [ 0.058589] [<c10223bc>] io_apic_setup_irq_pin+0x2c/0x310 >> [ 0.060042] [<c20638df>] setup_IO_APIC+0x101/0x744 >> [ 0.060878] [<c1021d51>] ? clear_IO_APIC+0x31/0x50 >> [ 0.061695] [<c20600f4>] native_smp_prepare_cpus+0x538/0x680 >> [ 0.062644] [<c2056a91>] ? do_one_initcall+0x12c/0x12c >> [ 0.063517] [<c2056a91>] ? do_one_initcall+0x12c/0x12c >> [ 0.064016] [<c2056adc>] kernel_init+0x4b/0x17f >> [ 0.064790] [<c2056a91>] ? do_one_initcall+0x12c/0x12c >> [ 0.065660] [<c1b2bbd6>] kernel_thread_helper+0x6/0x10 >> >> It was caused by that: >> >> native_smp_prepare_cpus() >> preempt_disable() //preempt_count++ >> mutex_lock() //in __irq_alloc_descs >> __might_sleep() //system is booting, avoid check >> might_resched() >> __schedule() >> preempt_disable() //preempt_count++ >> schedule_bug() //preempt_count > 1, report bug >> >> The __might_sleep() avoid check on atomic sleeping until the system booted >> while the schedule_bug() doesn't, it's the reason for the bug. >> >> This patch will add one additional check in schedule_bug() to avoid check >> until the system booted, so the check on atomic sleeping will be unified. >> >> Signed-off-by: Michael Wang <wangyun@linux.vnet.ibm.com> >> Tested-by: Fengguang Wu <wfg@linux.intel.com> >> --- >> kernel/sched/core.c | 3 ++- >> 1 files changed, 2 insertions(+), 1 deletions(-) >> >> diff --git a/kernel/sched/core.c b/kernel/sched/core.c >> index 4376c9f..3396c33 100644 >> --- a/kernel/sched/core.c >> +++ b/kernel/sched/core.c >> @@ -3321,7 +3321,8 @@ static inline void schedule_debug(struct task_struct *prev) >> * schedule() atomically, we ignore that path for now. >> * Otherwise, whine if we are scheduling when we should not be. >> */ >> - if (unlikely(in_atomic_preempt_off() && !prev->exit_state)) >> + if (unlikely(in_atomic_preempt_off() && !prev->exit_state >> + && system_state == SYSTEM_RUNNING)) >> __schedule_bug(prev); >> rcu_sleep_check(); >> > > > No this is very very wrong.. we avoid the might_sleep bug on ! > SYSTEM_RUNNING because while we _might_ sleep, we should _never_ > actually sleep under those conditions. > > So hitting a schedule() here is an actual bug.
I see, so the rule is that we never allowed invoke schedule() with preempt disabled.
The actual reason trigger this bug is that: we invoke irq_alloc_descs() which will use mutex_lock() while !SYSTEM_RUNNING. And mutex_lock() invoke the might_sleep(), which do the schedule() without any warning.
So if we want to follow the rule, should_resched() should never return true if preempt disabled.
I think we could do changes like:
index c46a011..36fe510 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4209,7 +4209,7 @@ SYSCALL_DEFINE0(sched_yield) static inline int should_resched(void) { - return need_resched() && !(preempt_count() & PREEMPT_ACTIVE); + return need_resched() && !preempt_count(); } static void __cond_resched(void)
Then the should_resched() will return false when the preempt disabled or PREEMPT_ACTIVE bit is on.
Could we use this solution?
Regards, Michael Wang
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