* Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > On Wed, 12 Nov 2008, Maciej Rutecki wrote: > > > -rc3 works OK > > > > I have this bug during suspend to disk: > > > > [ 188.592151] Enabling non-boot CPUs ... > > [ 188.592151] SMP alternatives: switching to SMP code > > [ 188.666058] BUG: using smp_processor_id() in preemptible [00000000] > > code: suspend_to_disk/2934 > > [ 188.666064] caller is native_sched_clock+0x2b/0x80 > > The cause seems to be commit > 7cbaef9c83e58bbd4bdd534b09052b6c5ec457d5, "sched: optimize > sched_clock() a bit" by Ingo. > > Which actually comments on the fact that a few callers may need to > be updated. That wasn't good. Ingo - it's not acceptable for a > latish-rc patch to introduce _known_ bugs and not fixing everything > up. > > Of course, since Maciej has frame pointers disabled, the stack trace > isn't entirely reliable, but it looks like the problem is > "init_idle()". > > That thing needs to call sched_clock() with interrupts disabled. > Looking at it, I'd also expect that it should have used > "sched_clock_cpu()", but I'm leaving that to Ingo to sort out. Ingo? i've queued up the fix below in tip/sched/urgent - Maciej, could you please test it? I've build and boot tested it. I picked the simplest solution - to widen the (init only) use of the rq lock there, which is irqsafe already. Another question is: how/where does the hibernation code call init_idle() with interrupts and preemption enabled? All the normal init_idle() sequences are called with irqs off (and at least with preemption off), that's why my testing didnt catch this bug. [ I was under the distinct illusion that i had all callers covered both via review and via testing (there's no that many users of naked sched_clock() left). So there was certainly no bug known to me - my comment was directed at out-of-tree naked-sched_clock() users which do exist. The recommended in-kernel API is cpu_clock(cpu) - except for scheduler-internal use which was the issue here. ] But it was still a late change and the boot warning was unnecessary, sorry about that. Ingo -------------> >From 5cbd54ef470d880fc37fbe4b21eb514806d51e0d Mon Sep 17 00:00:00 2001 From: Ingo Molnar <mingo@xxxxxxx> Date: Wed, 12 Nov 2008 20:05:50 +0100 Subject: [PATCH] sched: fix init_idle()'s use of sched_clock() Maciej Rutecki reported: > I have this bug during suspend to disk: > > [ 188.592151] Enabling non-boot CPUs ... > [ 188.592151] SMP alternatives: switching to SMP code > [ 188.666058] BUG: using smp_processor_id() in preemptible > [00000000] > code: suspend_to_disk/2934 > [ 188.666064] caller is native_sched_clock+0x2b/0x80 Which, as noted by Linus, was caused by me, via: 7cbaef9c "sched: optimize sched_clock() a bit" Move the rq locking a bit earlier in the initialization sequence, that will make the sched_clock() call in init_idle() non-preemptible. Reported-by: Maciej Rutecki <maciej.rutecki@xxxxxxxxx> Signed-off-by: Ingo Molnar <mingo@xxxxxxx> --- kernel/sched.c | 3 ++- 1 files changed, 2 insertions(+), 1 deletions(-) diff --git a/kernel/sched.c b/kernel/sched.c index 3bafbe3..c94baf2 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -5870,6 +5870,8 @@ void __cpuinit init_idle(struct task_struct *idle, int cpu) struct rq *rq = cpu_rq(cpu); unsigned long flags; + spin_lock_irqsave(&rq->lock, flags); + __sched_fork(idle); idle->se.exec_start = sched_clock(); @@ -5877,7 +5879,6 @@ void __cpuinit init_idle(struct task_struct *idle, int cpu) idle->cpus_allowed = cpumask_of_cpu(cpu); __set_task_cpu(idle, cpu); - spin_lock_irqsave(&rq->lock, flags); rq->curr = rq->idle = idle; #if defined(CONFIG_SMP) && defined(__ARCH_WANT_UNLOCKED_CTXSW) idle->oncpu = 1; -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
