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SubjectRe: [PATCH] sched: unify the check on atomic sleeping in __might_sleep() and schedule_bug()
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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.


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