Messages in this thread | | | Subject | Re: [PATCH] tracing: Fix lockdep warning in global_clock() | From | Steven Rostedt <> | Date | Mon, 21 Dec 2009 10:56:24 -0500 |
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On Mon, 2009-12-21 at 15:40 +0100, Peter Zijlstra wrote: > On Mon, 2009-12-21 at 15:36 +0800, Li Zefan wrote: > > > +++ 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? > > No, I removed the locks from cpu_clock a while back. >
The problem isn't with locks, it's with disabling interrupts. Lockdep keeps track of every time interrupts are disabled. If something disables interrupts with raw_* but then calls something that disables interrupts the normal way, lockdep will detect that interrupts are being disabled but they already are disabled. The internal irq disabled variable in lockdep wont match reality, and this will blow up (well, disable lockdep).
So if cpu_clock disables interrupts with local_irq_* then so must trace_clock_global.
-- Steve
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