Messages in this thread | | | Date | Thu, 19 Jul 2012 16:46:28 +0530 | From | "Naveen N. Rao" <> | Subject | Re: [PATCH v2 RESEND] Hardware breakpoints: Invoke __perf_event_disable() if interrupts are already disabled |
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On 07/18/2012 05:27 PM, Frederic Weisbecker wrote: > On Wed, Jul 18, 2012 at 04:00:46PM +0530, Naveen N. Rao wrote: >> Please find v2 of the patch from Prasad, based on Peter Zijlstra's >> feedback. This applies on top of v3.5-rc7. This has been tested and >> found to work fine by Edjunior. >> >> Regards, >> Naveen >> ______ >> >> From: K.Prasad <Prasad.Krishnan@gmail.com> >> >> While debugging a warning message on PowerPC while using hardware >> breakpoints, it was discovered that when perf_event_disable is invoked >> through hw_breakpoint_handler function with interrupts disabled, a >> subsequent IPI in the code path would trigger a WARN_ON_ONCE message in >> smp_call_function_single function. >> >> This patch calls __perf_event_disable() when interrupts are already >> disabled, instead of perf_event_disable(). >> >> Reported-by: Edjunior Barbosa Machado <emachado@linux.vnet.ibm.com> >> Signed-off-by: K.Prasad <Prasad.Krishnan@gmail.com> >> Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com> >> --- >> include/linux/perf_event.h | 2 ++ >> kernel/events/core.c | 2 +- >> kernel/events/hw_breakpoint.c | 10 +++++++++- >> 3 files changed, 12 insertions(+), 2 deletions(-) >> >> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h >> index 45db49f..c289ba0 100644 >> --- a/include/linux/perf_event.h >> +++ b/include/linux/perf_event.h >> @@ -1292,6 +1292,7 @@ extern int perf_swevent_get_recursion_context(void); >> extern void perf_swevent_put_recursion_context(int rctx); >> extern void perf_event_enable(struct perf_event *event); >> extern void perf_event_disable(struct perf_event *event); >> +extern int __perf_event_disable(void *info); >> extern void perf_event_task_tick(void); >> #else >> static inline void >> @@ -1330,6 +1331,7 @@ static inline int perf_swevent_get_recursion_context(void) { return -1; } >> static inline void perf_swevent_put_recursion_context(int rctx) { } >> static inline void perf_event_enable(struct perf_event *event) { } >> static inline void perf_event_disable(struct perf_event *event) { } >> +static inline int __perf_event_disable(void *info) { } >> static inline void perf_event_task_tick(void) { } >> #endif >> >> diff --git a/kernel/events/core.c b/kernel/events/core.c >> index d7d71d6..0ad0fc9 100644 >> --- a/kernel/events/core.c >> +++ b/kernel/events/core.c >> @@ -1253,7 +1253,7 @@ retry: >> /* >> * Cross CPU call to disable a performance event >> */ >> -static int __perf_event_disable(void *info) >> +int __perf_event_disable(void *info) >> { >> struct perf_event *event = info; >> struct perf_event_context *ctx = event->ctx; >> diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c >> index bb38c4d..483f14a 100644 >> --- a/kernel/events/hw_breakpoint.c >> +++ b/kernel/events/hw_breakpoint.c >> @@ -453,7 +453,15 @@ int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *att >> int old_type = bp->attr.bp_type; >> int err = 0; >> >> - perf_event_disable(bp); >> + /* >> + * modify_user_hw_breakpoint can be invoked with IRQs disabled and hence it >> + * will not be possible to raise IPIs that invoke __perf_event_disable. >> + * So call the function directly. >> + */ >> + if (irqs_disabled()) >> + __perf_event_disable(bp); >> + else >> + perf_event_disable(bp); > > This only works if we are sure the bp is on the current CPU. Do we > have that guarantee?
Yes. This is being hit during bp exception processing and is specific to ppc where we disable interrupts: hw_breakpoint_handler->perf_bp_event->ptrace_triggered->modify_user_hw_breakpoint()
Regards, Naveen
> >> >> bp->attr.bp_addr = attr->bp_addr; >> bp->attr.bp_type = attr->bp_type; >> >
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