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    Subject[PATCH v3] Hardware breakpoints: Invoke __perf_event_disable() if interrupts are already disabled
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    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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