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authorJens Axboe <axboe@fb.com>2014-04-24 08:51:47 -0600
committerJens Axboe <axboe@fb.com>2014-04-24 08:51:47 -0600
commit87ee7b112193bd081ba1a171fa5f6f39c429ef56 (patch)
treefbf88d2de279209467dee4d6cd9007f5daa8a678
parent70ab0b2d51f84fc7d9eb6ed81c3986595efaa33d (diff)
downloadop-kernel-dev-87ee7b112193bd081ba1a171fa5f6f39c429ef56.zip
op-kernel-dev-87ee7b112193bd081ba1a171fa5f6f39c429ef56.tar.gz
blk-mq: fix race with timeouts and requeue events
If a requeue event races with a timeout, we can get into the situation where we attempt to complete a request from the timeout handler when it's not start anymore. This causes a crash. So have the timeout handler check that REQ_ATOM_STARTED is still set on the request - if not, we ignore the event. If this happens, the request has now been marked as complete. As a consequence, we need to ensure to clear REQ_ATOM_COMPLETE in blk_mq_start_request(), as to maintain proper request state. Signed-off-by: Jens Axboe <axboe@fb.com>
-rw-r--r--block/blk-mq.c39
-rw-r--r--block/blk-mq.h2
-rw-r--r--block/blk-timeout.c16
-rw-r--r--block/blk.h3
4 files changed, 42 insertions, 18 deletions
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 7d5650d..a84112c 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -378,7 +378,15 @@ static void blk_mq_start_request(struct request *rq, bool last)
* REQ_ATOMIC_STARTED is seen.
*/
rq->deadline = jiffies + q->rq_timeout;
+
+ /*
+ * Mark us as started and clear complete. Complete might have been
+ * set if requeue raced with timeout, which then marked it as
+ * complete. So be sure to clear complete again when we start
+ * the request, otherwise we'll ignore the completion event.
+ */
set_bit(REQ_ATOM_STARTED, &rq->atomic_flags);
+ clear_bit(REQ_ATOM_COMPLETE, &rq->atomic_flags);
if (q->dma_drain_size && blk_rq_bytes(rq)) {
/*
@@ -485,6 +493,28 @@ static void blk_mq_hw_ctx_check_timeout(struct blk_mq_hw_ctx *hctx,
blk_mq_tag_busy_iter(hctx->tags, blk_mq_timeout_check, &data);
}
+static enum blk_eh_timer_return blk_mq_rq_timed_out(struct request *rq)
+{
+ struct request_queue *q = rq->q;
+
+ /*
+ * We know that complete is set at this point. If STARTED isn't set
+ * anymore, then the request isn't active and the "timeout" should
+ * just be ignored. This can happen due to the bitflag ordering.
+ * Timeout first checks if STARTED is set, and if it is, assumes
+ * the request is active. But if we race with completion, then
+ * we both flags will get cleared. So check here again, and ignore
+ * a timeout event with a request that isn't active.
+ */
+ if (!test_bit(REQ_ATOM_STARTED, &rq->atomic_flags))
+ return BLK_EH_NOT_HANDLED;
+
+ if (!q->mq_ops->timeout)
+ return BLK_EH_RESET_TIMER;
+
+ return q->mq_ops->timeout(rq);
+}
+
static void blk_mq_rq_timer(unsigned long data)
{
struct request_queue *q = (struct request_queue *) data;
@@ -538,11 +568,6 @@ static bool blk_mq_attempt_merge(struct request_queue *q,
return false;
}
-void blk_mq_add_timer(struct request *rq)
-{
- __blk_add_timer(rq, NULL);
-}
-
/*
* Run this hardware queue, pulling any software queues mapped to it in.
* Note that this function currently has various problems around ordering
@@ -799,7 +824,7 @@ static void __blk_mq_insert_request(struct blk_mq_hw_ctx *hctx,
/*
* We do this early, to ensure we are on the right CPU.
*/
- blk_mq_add_timer(rq);
+ blk_add_timer(rq);
}
void blk_mq_insert_request(struct request *rq, bool at_head, bool run_queue,
@@ -1400,7 +1425,7 @@ struct request_queue *blk_mq_init_queue(struct blk_mq_tag_set *set)
q->sg_reserved_size = INT_MAX;
blk_queue_make_request(q, blk_mq_make_request);
- blk_queue_rq_timed_out(q, set->ops->timeout);
+ blk_queue_rq_timed_out(q, blk_mq_rq_timed_out);
if (set->timeout)
blk_queue_rq_timeout(q, set->timeout);
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 5fa14f1..b41a784 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -51,6 +51,4 @@ void blk_mq_disable_hotplug(void);
extern unsigned int *blk_mq_make_queue_map(struct blk_mq_tag_set *set);
extern int blk_mq_update_queue_map(unsigned int *map, unsigned int nr_queues);
-void blk_mq_add_timer(struct request *rq);
-
#endif
diff --git a/block/blk-timeout.c b/block/blk-timeout.c
index a09e8af..49988a3 100644
--- a/block/blk-timeout.c
+++ b/block/blk-timeout.c
@@ -96,11 +96,7 @@ static void blk_rq_timed_out(struct request *req)
__blk_complete_request(req);
break;
case BLK_EH_RESET_TIMER:
- if (q->mq_ops)
- blk_mq_add_timer(req);
- else
- blk_add_timer(req);
-
+ blk_add_timer(req);
blk_clear_rq_complete(req);
break;
case BLK_EH_NOT_HANDLED:
@@ -170,7 +166,8 @@ void blk_abort_request(struct request *req)
}
EXPORT_SYMBOL_GPL(blk_abort_request);
-void __blk_add_timer(struct request *req, struct list_head *timeout_list)
+static void __blk_add_timer(struct request *req,
+ struct list_head *timeout_list)
{
struct request_queue *q = req->q;
unsigned long expiry;
@@ -225,6 +222,11 @@ void __blk_add_timer(struct request *req, struct list_head *timeout_list)
*/
void blk_add_timer(struct request *req)
{
- __blk_add_timer(req, &req->q->timeout_list);
+ struct request_queue *q = req->q;
+
+ if (q->mq_ops)
+ __blk_add_timer(req, NULL);
+ else
+ __blk_add_timer(req, &req->q->timeout_list);
}
diff --git a/block/blk.h b/block/blk.h
index 1d880f1..79be2cb 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -37,9 +37,8 @@ bool __blk_end_bidi_request(struct request *rq, int error,
void blk_rq_timed_out_timer(unsigned long data);
void blk_rq_check_expired(struct request *rq, unsigned long *next_timeout,
unsigned int *next_set);
-void __blk_add_timer(struct request *req, struct list_head *timeout_list);
+void blk_add_timer(struct request *req);
void blk_delete_timer(struct request *);
-void blk_add_timer(struct request *);
bool bio_attempt_front_merge(struct request_queue *q, struct request *req,
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