From: Josef Bacik <jo...@toxicpanda.com> Oleg noticed that our checking of data.got_token is unsafe in the cleanup case, and should really use a memory barrier. Use a wmb on the write side, and a rmb() on the read side. We don't need one in the main loop since we're saved by set_current_state().
Reviewed-by: Oleg Nesterov <o...@redhat.com> Signed-off-by: Josef Bacik <jo...@toxicpanda.com> Signed-off-by: Jens Axboe <ax...@kernel.dk> Changes when porting to vz7: - original patch is patching block/blk-rq-qos.c:rq_qos_wait, but in vz7 similar hunk is in block/blk-wbt.c:__wbt_wait - also original patch is patching rq_qos_wake_function, but in vz7 similar hunk is in wbt_wake_function https://jira.sw.ru/browse/PSBM-141883 (cherry picked from commit ac38297f7038cd5b80d66f8809c7bbf5b70031f3) Signed-off-by: Pavel Tikhomirov <ptikhomi...@virtuozzo.com> --- block/blk-wbt.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/block/blk-wbt.c b/block/blk-wbt.c index 4c5b6899db71..099678cd0d04 100644 --- a/block/blk-wbt.c +++ b/block/blk-wbt.c @@ -541,6 +541,7 @@ static int wbt_wake_function(struct __wait_queue *curr, unsigned int mode, return -1; data->got_token = true; + smp_wmb(); list_del_init(&curr->task_list); wake_up_process(data->task); return 1; @@ -573,6 +574,7 @@ static void __wbt_wait(struct rq_wb *rwb, enum wbt_flags wb_acct, prepare_to_wait_exclusive(&rqw->wait, &data.wq, TASK_UNINTERRUPTIBLE); has_sleeper = !wq_has_single_sleeper(&rqw->wait); do { + /* The memory barrier in set_task_state saves us here. */ if (data.got_token) break; @@ -585,6 +587,7 @@ static void __wbt_wait(struct rq_wb *rwb, enum wbt_flags wb_acct, * which means we now have two. Put our local token * and wake anyone else potentially waiting for one. */ + smp_rmb(); if (data.got_token) wbt_rqw_done(rwb, rqw, wb_acct); break; -- 2.37.1 _______________________________________________ Devel mailing list Devel@openvz.org https://lists.openvz.org/mailman/listinfo/devel
