diff options
| author |   Alexander Kabaev <kan@freebsd.org> | 2019-11-01 18:26:20 -0400 |
|---|---|---|
| committer | Alexander Kabaev <kan@freebsd.org> | 2019-11-01 21:57:49 -0400 |
| commit | feda545105106d673fdca61028331c86eeb1f408 (patch) | |
| tree | 74cb9790744d3f73ac6145910543196bf7ee5c9c | |
| parent | 5bec5f7860dafcef6aefd50b74de15d08910c6f4 (diff) | |
vlib: Handle race in thread barrier processing
When CLIB_DEBUG is enabled, vlib_foreach_main macro asserts that
vlib_main it currently looks at is safely parked in barrier, by
checkling that vlib_main->parked_at_barrier is not 0.
Unfortunately, the check is racy - workers first increment the
atomic counter to indicate that they have reached the barrier
and _then_ set this_main->parked_at_barrier to 1. For the last
worker to suspend this opens the race - main thread is free
to execute and assert immediately after atomic counter has been
incremented, before worker gets to write to own parked_at_barrier.
Fix this by simply swapping the order of two operations.
Type: fix
Signed-off-by: Alexnader Kabaev <kan@FreeBSD.org>
Change-Id: Iae47abd6ca0be1c5413f5ecaefabc64cd7eac2ed
| -rw-r--r-- | src/vlib/threads.h | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/src/vlib/threads.h b/src/vlib/threads.h index 79f44c8f502..312323c096d 100644 --- a/src/vlib/threads.h +++ b/src/vlib/threads.h @@ -416,12 +416,12 @@ vlib_worker_thread_barrier_check (void) ed->thread_index = thread_index; } - clib_atomic_fetch_add (vlib_worker_threads->workers_at_barrier, 1); if (CLIB_DEBUG > 0) { vm = vlib_get_main (); vm->parked_at_barrier = 1; } + clib_atomic_fetch_add (vlib_worker_threads->workers_at_barrier, 1); while (*vlib_worker_threads->wait_at_barrier) ; |