The normal request completion can be done before or during handling
BLK_EH_RESET_TIMER, and this race may cause the request to never
be completed since driver's .timeout() may always return
BLK_EH_RESET_TIMER.
This issue can't be fixed completely by driver, since the normal
completion can be done between returning .timeout() and handling
BLK_EH_RESET_TIMER.
This patch fixes the race by introducing rq state of MQ_RQ_COMPLETE_IN_RESET,
and reading/writing rq's state by holding queue lock, which can be
per-request actually, but just not necessary to introduce one lock for
so unusual event.
Also when .timeout() returns BLK_EH_HANDLED, sync with normal completion
path before completing this timed-out rq finally for avoiding this rq's
state touched by normal completion.
Cc: "jianchao.wang" <jianchao.w.wang@xxxxxxxxxx>
Cc: Bart Van Assche <bart.vanassche@xxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Ming Lei <ming.lei@xxxxxxxxxx>
Cc: Sagi Grimberg <sagi@xxxxxxxxxxx>
Cc: Israel Rukshin <israelr@xxxxxxxxxxxx>,
Cc: Max Gurtovoy <maxg@xxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
---
V3:
- before completing rq for BLK_EH_HANDLED, sync with normal
completion path
- make sure rq's state updated as MQ_RQ_IN_FLIGHT before completing
V2:
- rename the new flag as MQ_RQ_COMPLETE_IN_TIMEOUT
- fix lock uses in blk_mq_rq_timed_out
- document re-order between blk_add_timer() and
blk_mq_rq_update_aborted_gstate(req, 0)
block/blk-mq.c | 85 +++++++++++++++++++++++++++++++++++++++++++++++-----------
block/blk-mq.h | 1 +
2 files changed, 70 insertions(+), 16 deletions(-)
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 0dc9e341c2a7..d70f69a32226 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -198,23 +198,12 @@ void blk_mq_quiesce_queue_nowait(struct request_queue *q)
}
EXPORT_SYMBOL_GPL(blk_mq_quiesce_queue_nowait);
-/**
- * blk_mq_quiesce_queue() - wait until all ongoing dispatches have finished
- * @q: request queue.
- *
- * Note: this function does not prevent that the struct request end_io()
- * callback function is invoked. Once this function is returned, we make
- * sure no dispatch can happen until the queue is unquiesced via
- * blk_mq_unquiesce_queue().
- */
-void blk_mq_quiesce_queue(struct request_queue *q)
+static void blk_mq_queue_synchronize_rcu(struct request_queue *q)
{
struct blk_mq_hw_ctx *hctx;
unsigned int i;
bool rcu = false;
- blk_mq_quiesce_queue_nowait(q);
-
queue_for_each_hw_ctx(q, hctx, i) {
if (hctx->flags & BLK_MQ_F_BLOCKING)
synchronize_srcu(hctx->srcu);
@@ -224,6 +213,21 @@ void blk_mq_quiesce_queue(struct request_queue *q)
if (rcu)
synchronize_rcu();
}
+
+/**
+ * blk_mq_quiesce_queue() - wait until all ongoing dispatches have finished
+ * @q: request queue.
+ *
+ * Note: this function does not prevent that the struct request end_io()
+ * callback function is invoked. Once this function is returned, we make
+ * sure no dispatch can happen until the queue is unquiesced via
+ * blk_mq_unquiesce_queue().
+ */
+void blk_mq_quiesce_queue(struct request_queue *q)
+{
+ blk_mq_quiesce_queue_nowait(q);
+ blk_mq_queue_synchronize_rcu(q);
+}
EXPORT_SYMBOL_GPL(blk_mq_quiesce_queue);
/*
@@ -630,10 +634,27 @@ void blk_mq_complete_request(struct request *rq)
* However, that would complicate paths which want to synchronize
* against us. Let stay in sync with the issue path so that
* hctx_lock() covers both issue and completion paths.
+ *
+ * Cover complete vs BLK_EH_RESET_TIMER race in slow path with
+ * holding queue lock.
*/
hctx_lock(hctx, &srcu_idx);
if (blk_mq_rq_aborted_gstate(rq) != rq->gstate)
__blk_mq_complete_request(rq);
+ else {
+ unsigned long flags;
+ bool need_complete = false;
+
+ spin_lock_irqsave(q->queue_lock, flags);
+ if (!blk_mq_rq_aborted_gstate(rq))
+ need_complete = true;
+ else
+ blk_mq_rq_update_state(rq, MQ_RQ_COMPLETE_IN_TIMEOUT);
+ spin_unlock_irqrestore(q->queue_lock, flags);
+
+ if (need_complete)
+ __blk_mq_complete_request(rq);
+ }
hctx_unlock(hctx, srcu_idx);
}
EXPORT_SYMBOL(blk_mq_complete_request);
@@ -814,6 +835,7 @@ static void blk_mq_rq_timed_out(struct request *req, bool reserved)
{
const struct blk_mq_ops *ops = req->q->mq_ops;
enum blk_eh_timer_return ret = BLK_EH_RESET_TIMER;
+ unsigned long flags;
req->rq_flags |= RQF_MQ_TIMEOUT_EXPIRED;
@@ -822,16 +844,47 @@ static void blk_mq_rq_timed_out(struct request *req, bool reserved)
switch (ret) {
case BLK_EH_HANDLED:
+ /*
+ * If .timeout returns BLK_EH_HANDLED, this rq shouldn't
+ * be completed by normal irq context any more, but for
+ * the sake of safety, sync with normal completion path
+ * before completing this request finally because the
+ * normal completion path may touch this rq's state.
+ */
+ blk_mq_queue_synchronize_rcu(req->q);
+
+ spin_lock_irqsave(req->q->queue_lock, flags);
+ complete_rq:
+ if (blk_mq_rq_state(req) == MQ_RQ_COMPLETE_IN_TIMEOUT)
+ blk_mq_rq_update_state(req, MQ_RQ_IN_FLIGHT);
+ spin_unlock_irqrestore(req->q->queue_lock, flags);
__blk_mq_complete_request(req);
break;
case BLK_EH_RESET_TIMER:
/*
- * As nothing prevents from completion happening while
- * ->aborted_gstate is set, this may lead to ignored
- * completions and further spurious timeouts.
+ * The normal completion may happen during handling the
+ * timeout, or even after returning from .timeout(), so
+ * once the request has been completed, we can't reset
+ * timer any more since this request may be handled as
+ * BLK_EH_RESET_TIMER in next timeout handling too, and
+ * it has to be completed in this situation.
+ *
+ * Holding the queue lock to cover read/write rq's
+ * aborted_gstate and normal state, so the race can be
+ * avoided completely.
+ *
+ * blk_add_timer() may be re-ordered with resetting
+ * aborted_gstate, and the only side-effec is that if this
+ * request is recycled after aborted_gstate is cleared, it
+ * may be timed out a bit late, that is what we can survive
+ * given timeout event is so unusual.
*/
- blk_mq_rq_update_aborted_gstate(req, 0);
+ spin_lock_irqsave(req->q->queue_lock, flags);
+ if (blk_mq_rq_state(req) == MQ_RQ_COMPLETE_IN_TIMEOUT)
+ goto complete_rq;
blk_add_timer(req);
+ blk_mq_rq_update_aborted_gstate(req, 0);
+ spin_unlock_irqrestore(req->q->queue_lock, flags);
break;
case BLK_EH_NOT_HANDLED:
break;
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 88c558f71819..0426d048743d 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -35,6 +35,7 @@ enum mq_rq_state {
MQ_RQ_IDLE = 0,
MQ_RQ_IN_FLIGHT = 1,
MQ_RQ_COMPLETE = 2,
+ MQ_RQ_COMPLETE_IN_TIMEOUT = 3,
MQ_RQ_STATE_BITS = 2,
MQ_RQ_STATE_MASK = (1 << MQ_RQ_STATE_BITS) - 1,
--
2.9.5
