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authorThomas Gleixner <tglx@linutronix.de>2010-11-24 10:05:55 +0100
committerIngo Molnar <mingo@elte.hu>2010-11-26 15:00:56 +0100
commitdddd3379a619a4cb8247bfd3c94ca9ae3797aa2e (patch)
tree9b090784b46956d236b51c4addfcd97f575f205e /kernel
parent02a9d03772aa1ff33a26180a2da0bfb191240eda (diff)
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perf: Fix inherit vs. context rotation bug
It was found that sometimes children of tasks with inherited events had one extra event. Eventually it turned out to be due to the list rotation no being exclusive with the list iteration in the inheritance code. Cure this by temporarily disabling the rotation while we inherit the events. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <new-submission> Cc: <stable@kernel.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/perf_event.c22
1 files changed, 20 insertions, 2 deletions
diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 671f6c8c8a3..f365dd8ef8b 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -1622,8 +1622,12 @@ static void rotate_ctx(struct perf_event_context *ctx)
{
raw_spin_lock(&ctx->lock);
- /* Rotate the first entry last of non-pinned groups */
- list_rotate_left(&ctx->flexible_groups);
+ /*
+ * Rotate the first entry last of non-pinned groups. Rotation might be
+ * disabled by the inheritance code.
+ */
+ if (!ctx->rotate_disable)
+ list_rotate_left(&ctx->flexible_groups);
raw_spin_unlock(&ctx->lock);
}
@@ -6162,6 +6166,7 @@ int perf_event_init_context(struct task_struct *child, int ctxn)
struct perf_event *event;
struct task_struct *parent = current;
int inherited_all = 1;
+ unsigned long flags;
int ret = 0;
child->perf_event_ctxp[ctxn] = NULL;
@@ -6202,6 +6207,15 @@ int perf_event_init_context(struct task_struct *child, int ctxn)
break;
}
+ /*
+ * We can't hold ctx->lock when iterating the ->flexible_group list due
+ * to allocations, but we need to prevent rotation because
+ * rotate_ctx() will change the list from interrupt context.
+ */
+ raw_spin_lock_irqsave(&parent_ctx->lock, flags);
+ parent_ctx->rotate_disable = 1;
+ raw_spin_unlock_irqrestore(&parent_ctx->lock, flags);
+
list_for_each_entry(event, &parent_ctx->flexible_groups, group_entry) {
ret = inherit_task_group(event, parent, parent_ctx,
child, ctxn, &inherited_all);
@@ -6209,6 +6223,10 @@ int perf_event_init_context(struct task_struct *child, int ctxn)
break;
}
+ raw_spin_lock_irqsave(&parent_ctx->lock, flags);
+ parent_ctx->rotate_disable = 0;
+ raw_spin_unlock_irqrestore(&parent_ctx->lock, flags);
+
child_ctx = child->perf_event_ctxp[ctxn];
if (child_ctx && inherited_all) {