4.4-stable review patch. If anyone has any objections, please let me know.
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[ Upstream commit dcb10a967ce82d5ad20570693091139ae716ff76 ]
When ring buffer's AUX area is unmapped and rb->aux_mmap_count drops to zero, new AUX transactions into this buffer can still be started, even though the buffer in en route to deallocation.
This patch adds a check to perf_aux_output_begin() for rb->aux_mmap_count being zero, in which case there is no point starting new transactions, in other words, the ring buffers that pass a certain point in perf_mmap_close will not have their events sending new data, which clears path for freeing those buffers' pages right there and then, provided that no active transactions are holding the AUX reference.
Signed-off-by: Alexander Shishkin alexander.shishkin@linux.intel.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Cc: Arnaldo Carvalho de Melo acme@infradead.org 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 Cc: Vince Weaver vincent.weaver@maine.edu Cc: vince@deater.net Link: http://lkml.kernel.org/r/1457098969-21595-2-git-send-email-alexander.shishki... Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/events/ring_buffer.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c index 94dc6b0763ab..7324d83d6bd8 100644 --- a/kernel/events/ring_buffer.c +++ b/kernel/events/ring_buffer.c @@ -288,6 +288,13 @@ void *perf_aux_output_begin(struct perf_output_handle *handle, if (!rb_has_aux(rb) || !atomic_inc_not_zero(&rb->aux_refcount)) goto err;
+ /* + * If rb::aux_mmap_count is zero (and rb_has_aux() above went through), + * the aux buffer is in perf_mmap_close(), about to get freed. + */ + if (!atomic_read(&rb->aux_mmap_count)) + goto err; + /* * Nesting is not supported for AUX area, make sure nested * writers are caught early