4.4-stable review patch. If anyone has any objections, please let me know.
------------------ [ 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 <[email protected]> Signed-off-by: Peter Zijlstra (Intel) <[email protected]> Cc: Arnaldo Carvalho de Melo <[email protected]> Cc: Arnaldo Carvalho de Melo <[email protected]> Cc: Jiri Olsa <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Stephane Eranian <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Vince Weaver <[email protected]> Cc: [email protected] Link: http://lkml.kernel.org/r/1457098969-21595-2-git-send-email-alexander.shish...@linux.intel.com Signed-off-by: Ingo Molnar <[email protected]> Signed-off-by: Sasha Levin <[email protected]> --- 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 -- 2.19.1
