perf/hwpb: Invoke __perf_event_disable() if interrupts are already disabled

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>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20120802081635.5811.17737.stgit@localhost.localdomain
[ Fixed build error on MIPS. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 11 insertions, 2 deletions

diff --git a/kernel/events/core.c b/kernel/events/core.c
index efef4282b8e8..7fee567153f0 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 bb38c4d3ee12..9a7b487c6fe2 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;