Messages in this thread Patch in this message | | | Date | Mon, 21 Dec 2009 15:36:40 +0800 | From | Li Zefan <> | Subject | Re: [PATCH] tracing: Fix lockdep warning in global_clock() |
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Ingo Molnar wrote: > * Li Zefan <lizf@cn.fujitsu.com> wrote: > >> # echo 1 > events/enable >> # echo global > trace_clock >> >> ------------[ cut here ]------------ >> WARNING: at kernel/lockdep.c:3162 check_flags+0xb2/0x190() >> ... >> ---[ end trace 3f86734a89416623 ]--- >> possible reason: unannotated irqs-on. >> ... >> >> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com> >> --- >> kernel/trace/trace_clock.c | 4 ++-- >> 1 files changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/kernel/trace/trace_clock.c b/kernel/trace/trace_clock.c >> index 84a3a7b..11563c9 100644 >> --- a/kernel/trace/trace_clock.c >> +++ b/kernel/trace/trace_clock.c >> @@ -83,7 +83,7 @@ u64 notrace trace_clock_global(void) >> int this_cpu; >> u64 now; >> >> - raw_local_irq_save(flags); >> + local_irq_save(flags); > > Hm, wont this cause problems when we trace inside lockdep? Have you tried the > lockdep events - do they still work? >
Yes, they still work.
trace_clock_global() calls cpu_clock() which calls local_irq_save(), which causes this lockdep warning.
And I noticed this commit:
=============================================== commit 2d452c9b10caeec455eb5e56a0ef4ed485178213 Author: Ingo Molnar <mingo@elte.hu> Date: Sun Jun 29 15:01:59 2008 +0200
sched: sched_clock_cpu() based cpu_clock(), lockdep fix
Vegard Nossum reported:
> WARNING: at kernel/lockdep.c:2738 check_flags+0x142/0x160()
which happens due to:
unsigned long long cpu_clock(int cpu) { unsigned long long clock; unsigned long flags;
raw_local_irq_save(flags);
as lower level functions can take locks, we must not do that, use proper lockdep-annotated irq save/restore.
Reported-by: Vegard Nossum <vegard.nossum@gmail.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/sched_clock.c b/kernel/sched_clock.c index ed5a8c4..60094e2 100644 --- a/kernel/sched_clock.c +++ b/kernel/sched_clock.c @@ -250,9 +250,9 @@ unsigned long long cpu_clock(int cpu) unsigned long long clock; unsigned long flags;
- raw_local_irq_save(flags); + local_irq_save(flags); clock = sched_clock_cpu(cpu); - raw_local_irq_restore(flags); + local_irq_restore(flags);
return clock; } =============================================== I guess it's still true that lower level functions can take locks?
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