blk-wbt: fix IO hang in wbt_wait()

On wbt invariant is that if one IO is tracked via WBT_TRACKED, rqw->inflight
should be updated for tracking this IO.

But commit c1c80384c8f ("block: remove external dependency on wbt_flags")
forgets to remove the early handling of !rwb_enabled(rwb) inside wbt_wait(),
then the inflight counter may not be increased in wbt_wait(), but decreased
in wbt_done() for this kind of IO, so this counter may become negative, then
wbt_wait() may wait forever.

This patch fixes the report in the following link:

	https://marc.info/?l=linux-block&m=153221542021033&w=2

Fixes: c1c80384c8f ("block: remove external dependency on wbt_flags")
Cc: Josef Bacik <jbacik@fb.com>
Reported-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-wbt.c b/block/blk-wbt.c
index 1d94a20374fcbf2108edd4d54927ad4b0d5c4647..bb93c7c2b182bc8efee456bb64c4da5f05939e3c 100644 (file)
--- a/block/blk-wbt.c
+++ b/block/blk-wbt.c
@@ -576,12 +576,8 @@ static void wbt_wait(struct rq_qos *rqos, struct bio *bio, spinlock_t *lock)
        struct rq_wb *rwb = RQWB(rqos);
        enum wbt_flags flags;
 
-       if (!rwb_enabled(rwb))
-               return;
-
        flags = bio_to_wbt_flags(rwb, bio);
-
-       if (!wbt_should_throttle(rwb, bio)) {
+       if (!(flags & WBT_TRACKED)) {
                if (flags & WBT_READ)
                        wb_timestamp(rwb, &rwb->last_issue);
                return;