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Subject[PATCH 4.7 056/143] perf/core: Fix event_function_local()
Date
4.7-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Peter Zijlstra <peterz@infradead.org>

commit cca2094605efe6ccf43ff2876dd5bccc799202d8 upstream.

Vincent reported triggering the WARN_ON_ONCE() in event_function_local().

While thinking through cases I noticed that by using event_function()
directly, we miss the inactive case usually handled by
event_function_call().

Therefore construct a blend of event_function_call() and
event_function() that handles the cases relevant to
event_function_local().

Reported-by: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: fae3fde65138 ("perf: Collapse and fix event_function_call() users")
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
kernel/events/core.c | 60 ++++++++++++++++++++++++++++++++++++++++-----------
1 file changed, 48 insertions(+), 12 deletions(-)

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -242,18 +242,6 @@ unlock:
return ret;
}

-static void event_function_local(struct perf_event *event, event_f func, void *data)
-{
- struct event_function_struct efs = {
- .event = event,
- .func = func,
- .data = data,
- };
-
- int ret = event_function(&efs);
- WARN_ON_ONCE(ret);
-}
-
static void event_function_call(struct perf_event *event, event_f func, void *data)
{
struct perf_event_context *ctx = event->ctx;
@@ -303,6 +291,54 @@ again:
raw_spin_unlock_irq(&ctx->lock);
}

+/*
+ * Similar to event_function_call() + event_function(), but hard assumes IRQs
+ * are already disabled and we're on the right CPU.
+ */
+static void event_function_local(struct perf_event *event, event_f func, void *data)
+{
+ struct perf_event_context *ctx = event->ctx;
+ struct perf_cpu_context *cpuctx = __get_cpu_context(ctx);
+ struct task_struct *task = READ_ONCE(ctx->task);
+ struct perf_event_context *task_ctx = NULL;
+
+ WARN_ON_ONCE(!irqs_disabled());
+
+ if (task) {
+ if (task == TASK_TOMBSTONE)
+ return;
+
+ task_ctx = ctx;
+ }
+
+ perf_ctx_lock(cpuctx, task_ctx);
+
+ task = ctx->task;
+ if (task == TASK_TOMBSTONE)
+ goto unlock;
+
+ if (task) {
+ /*
+ * We must be either inactive or active and the right task,
+ * otherwise we're screwed, since we cannot IPI to somewhere
+ * else.
+ */
+ if (ctx->is_active) {
+ if (WARN_ON_ONCE(task != current))
+ goto unlock;
+
+ if (WARN_ON_ONCE(cpuctx->task_ctx != ctx))
+ goto unlock;
+ }
+ } else {
+ WARN_ON_ONCE(&cpuctx->ctx != ctx);
+ }
+
+ func(event, cpuctx, ctx, data);
+unlock:
+ perf_ctx_unlock(cpuctx, task_ctx);
+}
+
#define PERF_FLAG_ALL (PERF_FLAG_FD_NO_GROUP |\
PERF_FLAG_FD_OUTPUT |\
PERF_FLAG_PID_CGROUP |\

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