| Message ID | 20090616142217.GA5548@sig21.net (mailing list archive) |
|---|---|
| State | RFC, archived |
| Headers | show |
On Tue, 16 Jun 2009 16:22:17 +0200 Johannes Stezenbach <js@sig21.net> wrote: > Fix swsusp failure on !SMP > > Commit 01599fca6758d2cd133e78f87426fc851c9ea725 introduced > a regression which caused a backtrace on suspend and > a hang on resume on a Thinkpad T42p (Pentium M CPU). > > Signed-off-by: Johannes Stezenbach <js@sig21.net> > > > --- linux-2.6.30/kernel/up.c.orig 2009-06-16 15:56:28.000000000 +0200 > +++ linux-2.6.30/kernel/up.c 2009-06-16 15:57:27.000000000 +0200 > @@ -10,11 +10,13 @@ > int smp_call_function_single(int cpu, void (*func) (void *info), void *info, > int wait) > { > + unsigned long flags; > + > WARN_ON(cpu != 0); > > - local_irq_disable(); > + local_irq_save(flags); > (func)(info); > - local_irq_enable(); > + local_irq_restore(flags); > > return 0; > } ok, what's going on here? The patch implies that someone (presumably acpi-cpufreq) is calling smp_call_function_single() with local interrupts disabled. That's a bug on SMP kernels. And it'll generate a trace if it happens: /* Can deadlock when called with interrupts disabled */ WARN_ON_ONCE(irqs_disabled() && !oops_in_progress); but nobody has reported such a trace AFAIK? Also, prior to 01599fca6758d2cd133e78f87426fc851c9ea725, acpi-cpufreq was using work_on_cpu(). If it was calling work_on_cpu() with local interrupts disabled then that would have been a bug too, which could generate might_sleep() or scheduling-while-atomic warnings. Because it is a bug to call the SMP version of smp_call_function_single() with local interrupts disabled, I don't think we should need to apply the above patch. But I don't know what we _should_ do because I don't know what the bug is. Are you able to get us a copy of that stack trace? -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Tue, Jun 16, 2009 at 11:55:40AM -0700, Andrew Morton wrote: > On Tue, 16 Jun 2009 16:22:17 +0200 > Johannes Stezenbach <js@sig21.net> wrote: > > > Fix swsusp failure on !SMP > > > > Commit 01599fca6758d2cd133e78f87426fc851c9ea725 introduced > > a regression which caused a backtrace on suspend and > > a hang on resume on a Thinkpad T42p (Pentium M CPU). > > > > Signed-off-by: Johannes Stezenbach <js@sig21.net> > > > > > > --- linux-2.6.30/kernel/up.c.orig 2009-06-16 15:56:28.000000000 +0200 > > +++ linux-2.6.30/kernel/up.c 2009-06-16 15:57:27.000000000 +0200 > > @@ -10,11 +10,13 @@ > > int smp_call_function_single(int cpu, void (*func) (void *info), void *info, > > int wait) > > { > > + unsigned long flags; > > + > > WARN_ON(cpu != 0); > > > > - local_irq_disable(); > > + local_irq_save(flags); > > (func)(info); > > - local_irq_enable(); > > + local_irq_restore(flags); > > > > return 0; > > } > > ok, what's going on here? The patch implies that someone (presumably > acpi-cpufreq) is calling smp_call_function_single() with local > interrupts disabled. That's a bug on SMP kernels. And it'll generate > a trace if it happens: > > /* Can deadlock when called with interrupts disabled */ > WARN_ON_ONCE(irqs_disabled() && !oops_in_progress); > > but nobody has reported such a trace AFAIK? This problem apparently only exists on !SMP kernels... > Also, prior to 01599fca6758d2cd133e78f87426fc851c9ea725, acpi-cpufreq > was using work_on_cpu(). If it was calling work_on_cpu() with local > interrupts disabled then that would have been a bug too, which could > generate might_sleep() or scheduling-while-atomic warnings. On !SMP, work_on_cpu() is just a function call: http://lxr.linux.no/linux+v2.6.30/include/linux/workqueue.h#L261 > Because it is a bug to call the SMP version of > smp_call_function_single() with local interrupts disabled, I don't > think we should need to apply the above patch. and on SMP, smp_call_function_single() also uses local_irq_save/restore() iff cpu == this_cpu: http://lxr.linux.no/linux+v2.6.30/kernel/smp.c#L272 > But I don't know what we _should_ do because I don't know what the bug > is. Are you able to get us a copy of that stack trace? Unfortunately my laptop doesn't have a serial port, and the stack trace is large and scrolls off the screen, I can only see the last part of it and I would need to find someone with a camera to take a picture... Johannes -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
--- linux-2.6.30/kernel/up.c.orig 2009-06-16 15:56:28.000000000 +0200 +++ linux-2.6.30/kernel/up.c 2009-06-16 15:57:27.000000000 +0200 @@ -10,11 +10,13 @@ int smp_call_function_single(int cpu, void (*func) (void *info), void *info, int wait) { + unsigned long flags; + WARN_ON(cpu != 0); - local_irq_disable(); + local_irq_save(flags); (func)(info); - local_irq_enable(); + local_irq_restore(flags); return 0; }