Messages in this thread | | | Subject | Re: [Patch][perf] Invoke __perf_event_disable without an IPI | From | Peter Zijlstra <> | Date | Mon, 11 Jun 2012 13:13:33 +0200 |
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On Mon, 2012-06-11 at 11:32 +0530, K.Prasad wrote:
> 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()) {
Urgh..
So what's the callchain for the ppc->hw_bp->perf that triggers this?
> + ret = __perf_event_disable(event); > + if (!ret) > + return; > + } > if (!task_function_call(task, __perf_event_disable, event)) > return; > >
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