On Wed, 2012-08-22 at 10:40 +0800, Michael Wang wrote: > From: Michael Wang <wang...@linux.vnet.ibm.com> > > Fengguang Wu <w...@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 <wang...@linux.vnet.ibm.com> > Tested-by: Fengguang Wu <w...@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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
