From: Alexander Shishkin Date: Fri, 4 Mar 2016 13:42:45 +0000 (+0200) Subject: perf/ring_buffer: Refuse to begin AUX transaction after rb->aux_mmap_count drops X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=dcb10a967ce82d5ad20570693091139ae716ff76;p=openwrt%2Fstaging%2Fblogic.git perf/ring_buffer: Refuse to begin AUX transaction after rb->aux_mmap_count drops 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 Signed-off-by: Peter Zijlstra (Intel) Cc: Arnaldo Carvalho de Melo Cc: Arnaldo Carvalho de Melo Cc: Jiri Olsa Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Stephane Eranian Cc: Thomas Gleixner Cc: Vince Weaver Cc: vince@deater.net Link: http://lkml.kernel.org/r/1457098969-21595-2-git-send-email-alexander.shishkin@linux.intel.com Signed-off-by: Ingo Molnar --- diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c index c61f0cbd308b..89abf623e93c 100644 --- a/kernel/events/ring_buffer.c +++ b/kernel/events/ring_buffer.c @@ -287,6 +287,13 @@ 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