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authorAlexander Kabaev <kan@freebsd.org>2019-11-01 18:26:20 -0400
committerAlexander Kabaev <kan@freebsd.org>2019-11-01 21:57:49 -0400
commitfeda545105106d673fdca61028331c86eeb1f408 (patch)
tree74cb9790744d3f73ac6145910543196bf7ee5c9c /src/vlib/threads.h
parent5bec5f7860dafcef6aefd50b74de15d08910c6f4 (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
Diffstat (limited to 'src/vlib/threads.h')
-rw-r--r--src/vlib/threads.h2
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)
;