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authorYu Kuai <yukuai3@huawei.com>2022-05-13 04:35:07 +0200
committerJens Axboe <axboe@kernel.dk>2022-05-16 19:39:20 +0200
commitddc25c86b466d2359b57bc7798f167baa1735a44 (patch)
tree42e97d04b7d1155d8c68e00b876780930ed7bc61 /block
parentblock, bfq: protect 'bfqd->queued' by 'bfqd->lock' (diff)
downloadlinux-ddc25c86b466d2359b57bc7798f167baa1735a44.tar.xz
linux-ddc25c86b466d2359b57bc7798f167baa1735a44.zip
block, bfq: make bfq_has_work() more accurate
bfq_has_work() is using busy_queues currently, which is not accurate because bfq_queue is busy doesn't represent that it has requests. Since bfqd aready has a counter 'queued' to record how many requests are in bfq, use it instead of busy_queues. Noted that bfq_has_work() can be called with 'bfqd->lock' held, thus the lock can't be held in bfq_has_work() to protect 'bfqd->queued'. Signed-off-by: Yu Kuai <yukuai3@huawei.com> Reviewed-by: Jan Kara <jack@suse.cz> Link: https://lore.kernel.org/r/20220513023507.2625717-3-yukuai3@huawei.com Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block')
-rw-r--r--block/bfq-iosched.c16
1 files changed, 12 insertions, 4 deletions
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 62180dda6bf9..92f0a829a804 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -2204,7 +2204,11 @@ static void bfq_add_request(struct request *rq)
bfq_log_bfqq(bfqd, bfqq, "add_request %d", rq_is_sync(rq));
bfqq->queued[rq_is_sync(rq)]++;
- bfqd->queued++;
+ /*
+ * Updating of 'bfqd->queued' is protected by 'bfqd->lock', however, it
+ * may be read without holding the lock in bfq_has_work().
+ */
+ WRITE_ONCE(bfqd->queued, bfqd->queued + 1);
if (RB_EMPTY_ROOT(&bfqq->sort_list) && bfq_bfqq_sync(bfqq)) {
bfq_check_waker(bfqd, bfqq, now_ns);
@@ -2396,7 +2400,11 @@ static void bfq_remove_request(struct request_queue *q,
if (rq->queuelist.prev != &rq->queuelist)
list_del_init(&rq->queuelist);
bfqq->queued[sync]--;
- bfqd->queued--;
+ /*
+ * Updating of 'bfqd->queued' is protected by 'bfqd->lock', however, it
+ * may be read without holding the lock in bfq_has_work().
+ */
+ WRITE_ONCE(bfqd->queued, bfqd->queued - 1);
elv_rb_del(&bfqq->sort_list, rq);
elv_rqhash_del(q, rq);
@@ -5057,11 +5065,11 @@ static bool bfq_has_work(struct blk_mq_hw_ctx *hctx)
struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
/*
- * Avoiding lock: a race on bfqd->busy_queues should cause at
+ * Avoiding lock: a race on bfqd->queued should cause at
* most a call to dispatch for nothing
*/
return !list_empty_careful(&bfqd->dispatch) ||
- bfq_tot_busy_queues(bfqd) > 0;
+ READ_ONCE(bfqd->queued);
}
static struct request *__bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)