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SubjectRe: [PATCH v2 RESEND] Hardware breakpoints: Invoke __perf_event_disable() if interrupts are already disabled
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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