From: Ming Lei <ming.lei(a)redhat.com>
blk-mq: fix is_flush_rq
Bugzilla:
https://bugzilla.redhat.com/show_bug.cgi?id=1994424
Upstream Status: not merged to upstream, just posted on linux-block
is_flush_rq() is called from bt_iter()/bt_tags_iter(), and runs the
following check:
hctx->fq->flush_rq == req
but the passed hctx from bt_iter()/bt_tags_iter() may be NULL because:
1) memory re-order in blk_mq_rq_ctx_init():
rq->mq_hctx = data->hctx;
...
refcount_set(&rq->ref, 1);
OR
2) tag re-use and ->rqs[] isn't updated with new request.
Fix the issue by re-writing is_flush_rq() as:
return rq->end_io == flush_end_io;
which turns out simpler to follow and immune to data race since we have
ordered WRITE rq->end_io and refcount_set(&rq->ref, 1).
Fixes: 2e315dc07df0 ("blk-mq: grab rq->refcount before calling ->fn in
blk_mq_tagset_busy_iter")
Cc: "Blank-Burian, Markus, Dr." <blankburian(a)uni-muenster.de>
Cc: Yufen Yu <yuyufen(a)huawei.com>
Signed-off-by: Ming Lei <ming.lei(a)redhat.com>
diff --git a/block/blk-flush.c b/block/blk-flush.c
index blahblah..blahblah 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -262,6 +262,11 @@ static void flush_end_io(struct request *flush_rq, blk_status_t
error)
spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
}
+bool is_flush_rq(struct request *rq)
+{
+ return rq->end_io == flush_end_io;
+}
+
/**
* blk_kick_flush - consider issuing flush request
* @q: request_queue being kicked
diff --git a/block/blk-mq.c b/block/blk-mq.c
index blahblah..blahblah 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -911,7 +911,7 @@ static bool blk_mq_req_expired(struct request *rq, unsigned long
*next)
void blk_mq_put_rq_ref(struct request *rq)
{
- if (is_flush_rq(rq, rq->mq_hctx))
+ if (is_flush_rq(rq))
rq->end_io(rq, 0);
else if (refcount_dec_and_test(&rq->ref))
__blk_mq_free_request(rq);
diff --git a/block/blk.h b/block/blk.h
index blahblah..blahblah 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -44,11 +44,7 @@ static inline void __blk_get_queue(struct request_queue *q)
kobject_get(&q->kobj);
}
-static inline bool
-is_flush_rq(struct request *req, struct blk_mq_hw_ctx *hctx)
-{
- return hctx->fq->flush_rq == req;
-}
+bool is_flush_rq(struct request *req);
struct blk_flush_queue *blk_alloc_flush_queue(int node, int cmd_size,
gfp_t flags);
--
https://gitlab.com/cki-project/kernel-ark/-/merge_requests/1315