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    SubjectRe: [PATCH v3] Hardware breakpoints: Invoke __perf_event_disable() if interrupts are already disabled
    Hi Frederick,
    Did you get a chance to take a look at this?

    Regards,
    Naveen

    On 08/02/2012 01:46 PM, Naveen N. Rao wrote:
    > Hi Frederick,
    > I've added a check to make sure we are targeting the current task. This
    > applies on top of v3.5. Kindly review.
    >
    > Thanks,
    > Naveen
    >
    > History:
    > v3: Added check to make sure we only target "current" task.
    > v2: Use __perf_event_disable() directly
    > ______
    >
    > 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>
    > [naveen.n.rao@linux.vnet.ibm.com: v3: Check to make sure we target current task]
    > 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 | 11 ++++++++++-
    > 3 files changed, 13 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..9a7b487 100644
    > --- a/kernel/events/hw_breakpoint.c
    > +++ b/kernel/events/hw_breakpoint.c
    > @@ -453,7 +453,16 @@ 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 after making sure we are targeting the
    > + * current task.
    > + */
    > + if (irqs_disabled() && bp->ctx && bp->ctx->task == current)
    > + __perf_event_disable(bp);
    > + else
    > + perf_event_disable(bp);
    >
    > bp->attr.bp_addr = attr->bp_addr;
    > bp->attr.bp_type = attr->bp_type;
    >



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