perf: Fix scaling vs. perf_install_in_context()
Completely reworks perf_install_in_context() (again!) in order to
ensure that there will be no ctx time hole between add_event_to_ctx()
and any potential ctx_sched_in().
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: Thomas Gleixner <tglx@linutronix.de>
Cc: dvyukov@google.com
Cc: eranian@google.com
Cc: oleg@redhat.com
Cc: panand@redhat.com
Cc: sasha.levin@oracle.com
Cc: vince@deater.net
Link: http://lkml.kernel.org/r/20160224174948.279399438@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 57c25fa..25edabd 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -276,10 +276,10 @@
return;
}
-again:
if (task == TASK_TOMBSTONE)
return;
+again:
if (!task_function_call(task, event_function, &efs))
return;
@@ -289,13 +289,15 @@
* a concurrent perf_event_context_sched_out().
*/
task = ctx->task;
- if (task != TASK_TOMBSTONE) {
- if (ctx->is_active) {
- raw_spin_unlock_irq(&ctx->lock);
- goto again;
- }
- func(event, NULL, ctx, data);
+ if (task == TASK_TOMBSTONE) {
+ raw_spin_unlock_irq(&ctx->lock);
+ return;
}
+ if (ctx->is_active) {
+ raw_spin_unlock_irq(&ctx->lock);
+ goto again;
+ }
+ func(event, NULL, ctx, data);
raw_spin_unlock_irq(&ctx->lock);
}
@@ -2116,49 +2118,68 @@
/*
* Cross CPU call to install and enable a performance event
*
- * Must be called with ctx->mutex held
+ * Very similar to remote_function() + event_function() but cannot assume that
+ * things like ctx->is_active and cpuctx->task_ctx are set.
*/
static int __perf_install_in_context(void *info)
{
- struct perf_event_context *ctx = info;
+ struct perf_event *event = info;
+ struct perf_event_context *ctx = event->ctx;
struct perf_cpu_context *cpuctx = __get_cpu_context(ctx);
struct perf_event_context *task_ctx = cpuctx->task_ctx;
+ bool activate = true;
+ int ret = 0;
raw_spin_lock(&cpuctx->ctx.lock);
if (ctx->task) {
raw_spin_lock(&ctx->lock);
- /*
- * If we hit the 'wrong' task, we've since scheduled and
- * everything should be sorted, nothing to do!
- */
task_ctx = ctx;
- if (ctx->task != current)
+
+ /* If we're on the wrong CPU, try again */
+ if (task_cpu(ctx->task) != smp_processor_id()) {
+ ret = -ESRCH;
goto unlock;
+ }
/*
- * If task_ctx is set, it had better be to us.
+ * If we're on the right CPU, see if the task we target is
+ * current, if not we don't have to activate the ctx, a future
+ * context switch will do that for us.
*/
- WARN_ON_ONCE(cpuctx->task_ctx != ctx && cpuctx->task_ctx);
+ if (ctx->task != current)
+ activate = false;
+ else
+ WARN_ON_ONCE(cpuctx->task_ctx && cpuctx->task_ctx != ctx);
+
} else if (task_ctx) {
raw_spin_lock(&task_ctx->lock);
}
- ctx_resched(cpuctx, task_ctx);
+ if (activate) {
+ ctx_sched_out(ctx, cpuctx, EVENT_TIME);
+ add_event_to_ctx(event, ctx);
+ ctx_resched(cpuctx, task_ctx);
+ } else {
+ add_event_to_ctx(event, ctx);
+ }
+
unlock:
perf_ctx_unlock(cpuctx, task_ctx);
- return 0;
+ return ret;
}
/*
- * Attach a performance event to a context
+ * Attach a performance event to a context.
+ *
+ * Very similar to event_function_call, see comment there.
*/
static void
perf_install_in_context(struct perf_event_context *ctx,
struct perf_event *event,
int cpu)
{
- struct task_struct *task = NULL;
+ struct task_struct *task = READ_ONCE(ctx->task);
lockdep_assert_held(&ctx->mutex);
@@ -2166,42 +2187,46 @@
if (event->cpu != -1)
event->cpu = cpu;
- /*
- * Installing events is tricky because we cannot rely on ctx->is_active
- * to be set in case this is the nr_events 0 -> 1 transition.
- *
- * So what we do is we add the event to the list here, which will allow
- * a future context switch to DTRT and then send a racy IPI. If the IPI
- * fails to hit the right task, this means a context switch must have
- * happened and that will have taken care of business.
- */
- raw_spin_lock_irq(&ctx->lock);
- task = ctx->task;
-
- /*
- * If between ctx = find_get_context() and mutex_lock(&ctx->mutex) the
- * ctx gets destroyed, we must not install an event into it.
- *
- * This is normally tested for after we acquire the mutex, so this is
- * a sanity check.
- */
- if (WARN_ON_ONCE(task == TASK_TOMBSTONE)) {
- raw_spin_unlock_irq(&ctx->lock);
+ if (!task) {
+ cpu_function_call(cpu, __perf_install_in_context, event);
return;
}
- if (ctx->is_active) {
- update_context_time(ctx);
- update_cgrp_time_from_event(event);
+ /*
+ * Should not happen, we validate the ctx is still alive before calling.
+ */
+ if (WARN_ON_ONCE(task == TASK_TOMBSTONE))
+ return;
+
+ /*
+ * Installing events is tricky because we cannot rely on ctx->is_active
+ * to be set in case this is the nr_events 0 -> 1 transition.
+ */
+again:
+ /*
+ * Cannot use task_function_call() because we need to run on the task's
+ * CPU regardless of whether its current or not.
+ */
+ if (!cpu_function_call(task_cpu(task), __perf_install_in_context, event))
+ return;
+
+ raw_spin_lock_irq(&ctx->lock);
+ task = ctx->task;
+ if (WARN_ON_ONCE(task == TASK_TOMBSTONE)) {
+ /*
+ * Cannot happen because we already checked above (which also
+ * cannot happen), and we hold ctx->mutex, which serializes us
+ * against perf_event_exit_task_context().
+ */
+ raw_spin_unlock_irq(&ctx->lock);
+ return;
}
-
- add_event_to_ctx(event, ctx);
raw_spin_unlock_irq(&ctx->lock);
-
- if (task)
- task_function_call(task, __perf_install_in_context, ctx);
- else
- cpu_function_call(cpu, __perf_install_in_context, ctx);
+ /*
+ * Since !ctx->is_active doesn't mean anything, we must IPI
+ * unconditionally.
+ */
+ goto again;
}
/*