From b79ccadd6bb10e72cf784a298ca6dc1398eb9a24 Mon Sep 17 00:00:00 2001 From: Alexander Shishkin Date: Tue, 6 Sep 2016 16:23:50 +0300 Subject: [PATCH] perf/core: Fix aux_mmap_count vs aux_refcount order The order of accesses to ring buffer's aux_mmap_count and aux_refcount has to be preserved across the users, namely perf_mmap_close() and perf_aux_output_begin(), otherwise the inversion can result in the latter holding the last reference to the aux buffer and subsequently free'ing it in atomic context, triggering a warning. > ------------[ cut here ]------------ > WARNING: CPU: 0 PID: 257 at kernel/events/ring_buffer.c:541 __rb_free_aux+0x11a/0x130 > CPU: 0 PID: 257 Comm: stopbug Not tainted 4.8.0-rc1+ #2596 > Call Trace: > [] __warn+0xcb/0xf0 > [] warn_slowpath_null+0x1d/0x20 > [] __rb_free_aux+0x11a/0x130 > [] rb_free_aux+0x18/0x20 > [] perf_aux_output_begin+0x163/0x1e0 > [] bts_event_start+0x3a/0xd0 > [] bts_event_add+0x5d/0x80 > [] event_sched_in.isra.104+0xf6/0x2f0 > [] group_sched_in+0x6e/0x190 > [] ctx_sched_in+0x2fe/0x5f0 > [] perf_event_sched_in+0x60/0x80 > [] ctx_resched+0x5b/0x90 > [] __perf_event_enable+0x1e1/0x240 > [] event_function+0xa9/0x180 > [] ? perf_cgroup_attach+0x70/0x70 > [] remote_function+0x3f/0x50 > [] flush_smp_call_function_queue+0x83/0x150 > [] generic_smp_call_function_single_interrupt+0x13/0x60 > [] smp_call_function_single_interrupt+0x27/0x40 > [] call_function_single_interrupt+0x89/0x90 > [] finish_task_switch+0xa6/0x210 > [] ? finish_task_switch+0x67/0x210 > [] __schedule+0x3dd/0xb50 > [] schedule+0x35/0x80 > [] sys_sched_yield+0x61/0x70 > [] entry_SYSCALL_64_fastpath+0x18/0xa8 > ---[ end trace 6235f556f5ea83a9 ]--- This patch puts the checks in perf_aux_output_begin() in the same order as that of perf_mmap_close(). Reported-by: Vince Weaver 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@deater.net Link: http://lkml.kernel.org/r/20160906132353.19887-3-alexander.shishkin@linux.intel.com Signed-off-by: Ingo Molnar --- kernel/events/ring_buffer.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-) diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c index ae9b90dc9a5a..257fa460b846 100644 --- a/kernel/events/ring_buffer.c +++ b/kernel/events/ring_buffer.c @@ -330,15 +330,22 @@ void *perf_aux_output_begin(struct perf_output_handle *handle, if (!rb) return NULL; - if (!rb_has_aux(rb) || !atomic_inc_not_zero(&rb->aux_refcount)) + if (!rb_has_aux(rb)) 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 aux_mmap_count is zero, the aux buffer is in perf_mmap_close(), + * about to get freed, so we leave immediately. + * + * Checking rb::aux_mmap_count and rb::refcount has to be done in + * the same order, see perf_mmap_close. Otherwise we end up freeing + * aux pages in this path, which is a bug, because in_atomic(). */ if (!atomic_read(&rb->aux_mmap_count)) - goto err_put; + goto err; + + if (!atomic_inc_not_zero(&rb->aux_refcount)) + goto err; /* * Nesting is not supported for AUX area, make sure nested