Factor out [s]rcu synchronization in blk_mq_timeout_work() into blk_mq_timeout_sync_rcu(). This is to add another user in the future and doesn't cause any functional changes. Signed-off-by: Tejun Heo <tj@xxxxxxxxxx> Cc: Bart Van Assche <Bart.VanAssche@xxxxxxx> --- Hello, We were tracking this down in the following thread http://lkml.kernel.org/r/20180207011133.25957-1-bart.vanassche@xxxxxxx but lost the reproducer in the middle and couldn't fully verify these two patches fix the problem; however, the identified race is real and a bug, so I think it'd be best to apply these two patches. Given the lack of further reports on this front, I don't think it's necessary to rush these patches. I think it'd be best to apply these once the merge window closes. If we need to backport these to -stable, we can tag them later. Thanks. block/blk-mq.c | 39 +++++++++++++++++++++++---------------- include/linux/blk-mq.h | 2 +- 2 files changed, 24 insertions(+), 17 deletions(-) --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -876,13 +876,34 @@ static void blk_mq_check_expired(struct time_after_eq(jiffies, deadline)) { blk_mq_rq_update_aborted_gstate(rq, gstate); data->nr_expired++; - hctx->nr_expired++; + hctx->need_sync_rcu = true; } else if (!data->next_set || time_after(data->next, deadline)) { data->next = deadline; data->next_set = 1; } } +static void blk_mq_timeout_sync_rcu(struct request_queue *q) +{ + struct blk_mq_hw_ctx *hctx; + bool has_rcu = false; + int i; + + queue_for_each_hw_ctx(q, hctx, i) { + if (!hctx->need_sync_rcu) + continue; + + if (!(hctx->flags & BLK_MQ_F_BLOCKING)) + has_rcu = true; + else + synchronize_srcu(hctx->srcu); + + hctx->need_sync_rcu = false; + } + if (has_rcu) + synchronize_rcu(); +} + static void blk_mq_terminate_expired(struct blk_mq_hw_ctx *hctx, struct request *rq, void *priv, bool reserved) { @@ -930,27 +951,13 @@ static void blk_mq_timeout_work(struct w blk_mq_queue_tag_busy_iter(q, blk_mq_check_expired, &data); if (data.nr_expired) { - bool has_rcu = false; - /* * Wait till everyone sees ->aborted_gstate. The * sequential waits for SRCUs aren't ideal. If this ever * becomes a problem, we can add per-hw_ctx rcu_head and * wait in parallel. */ - queue_for_each_hw_ctx(q, hctx, i) { - if (!hctx->nr_expired) - continue; - - if (!(hctx->flags & BLK_MQ_F_BLOCKING)) - has_rcu = true; - else - synchronize_srcu(hctx->srcu); - - hctx->nr_expired = 0; - } - if (has_rcu) - synchronize_rcu(); + blk_mq_timeout_sync_rcu(q); /* terminate the ones we won */ blk_mq_queue_tag_busy_iter(q, blk_mq_terminate_expired, NULL); --- a/include/linux/blk-mq.h +++ b/include/linux/blk-mq.h @@ -51,7 +51,7 @@ struct blk_mq_hw_ctx { unsigned int queue_num; atomic_t nr_active; - unsigned int nr_expired; + bool need_sync_rcu; struct hlist_node cpuhp_dead; struct kobject kobj;
