Messages in this thread Patch in this message | | | Date | Mon, 11 Jun 2012 11:32:42 +0530 | From | "K.Prasad" <> | Subject | [Patch][perf] Invoke __perf_event_disable without an IPI |
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Hi All, Please review the following patch, the details of which are described in the commit message below.
Basic perf commands (and memory tracing event '-e mem') were tested to work fine with this patch and can be applied over commit b1dab2f0409c478fd2d9e227c2c018524eca9603.
Kindly let me know if there could be a better approach or if there's a need for further testing.
Thanks, K.Prasad
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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 avoids the use of an IPI to invoke __perf_event_disable when it is safe to do so i.e. when the process associated with the perf-event would run on the current CPU and interrupts are disabled on the system. Since interrupts are always disabled before hw_breakpoint_handler in PowerPC, the warning message will no longer be seen.
Reported-by: Edjunior Barbosa Machado <emachado@linux.vnet.ibm.com> Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com> --- kernel/events/core.c | 12 ++++++++++++ 1 files changed, 12 insertions(+), 0 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c index fd126f8..0e2c1eb 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -1302,6 +1302,7 @@ static int __perf_event_disable(void *info) */ void perf_event_disable(struct perf_event *event) { + int ret; struct perf_event_context *ctx = event->ctx; struct task_struct *task = ctx->task; @@ -1314,6 +1315,17 @@ void perf_event_disable(struct perf_event *event) } retry: + /* + * perf_event_disable may be called when interrupts are disabled. + * For e.g. hw_breakpoint_handler exception in PowerPC. Hence using + * IPIs to invoke __perf_event_disable is not always suitable. When + * possible invoke __perf_event_disable directly. + */ + if ((task_cpu(task) == smp_processor_id()) && irqs_disabled()) { + ret = __perf_event_disable(event); + if (!ret) + return; + } if (!task_function_call(task, __perf_event_disable, event)) return;
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