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authorPeter Zijlstra <peterz@infradead.org>2015-09-09 20:48:22 +0200
committerIngo Molnar <mingo@kernel.org>2015-09-18 09:20:26 +0200
commitf73e22ab450140830005581c2c7ec389791a1b8d (patch)
tree78ff75731998d7b9cf2857b91ad4a944ce996f2c /kernel
parenta723968c0ed36db676478c3d26078f13484fe01c (diff)
perf: Fix races in computing the header sizes
There are two races with the current code: - Another event can join the group and compute a larger header_size concurrently, if the smaller store wins we'll have an incorrect header_size set. - We compute the header_size after the event becomes active, therefore its possible to use the size before its computed. Remedy the first by moving the computation inside the ctx::mutex lock, and the second by placing it _before_ perf_install_in_context(). Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Arnaldo Carvalho de Melo <acme@kernel.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/events/core.c15
1 files changed, 9 insertions, 6 deletions
diff --git a/kernel/events/core.c b/kernel/events/core.c
index dbb5329b6a3a..b11756f9b6dc 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -8399,6 +8399,15 @@ SYSCALL_DEFINE5(perf_event_open,
put_ctx(gctx);
}
+ /*
+ * Precalculate sample_data sizes; do while holding ctx::mutex such
+ * that we're serialized against further additions and before
+ * perf_install_in_context() which is the point the event is active and
+ * can use these values.
+ */
+ perf_event__header_size(event);
+ perf_event__id_header_size(event);
+
perf_install_in_context(ctx, event, event->cpu);
perf_unpin_context(ctx);
@@ -8415,12 +8424,6 @@ SYSCALL_DEFINE5(perf_event_open,
mutex_unlock(&current->perf_event_mutex);
/*
- * Precalculate sample_data sizes
- */
- perf_event__header_size(event);
- perf_event__id_header_size(event);
-
- /*
* Drop the reference on the group_event after placing the
* new event on the sibling_list. This ensures destruction
* of the group leader will find the pointer to itself in