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 handle the timeout requests in two steps:
1) in 1st step, call .timeout(), and reset timer for BLK_EH_RESET_TIMER
2) in 2nd step, sync with normal completion path by holding queue lock
for avoiding race between BLK_EH_RESET_TIMER and 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
Cc: Martin Steigerwald <Martin@xxxxxxxxxxxx>
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
---
block/blk-mq.c | 116 ++++++++++++++++++++++++++++++++++++++++---------
block/blk-mq.h | 1 +
include/linux/blkdev.h | 6 +++
3 files changed, 102 insertions(+), 21 deletions(-)
diff --git a/block/blk-mq.c b/block/blk-mq.c
index d6a21898933d..9415e65302a8 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -630,10 +630,27 @@ 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);
@@ -810,7 +827,7 @@ struct blk_mq_timeout_data {
unsigned int nr_expired;
};
-static void blk_mq_rq_timed_out(struct request *req, bool reserved)
+static void blk_mq_rq_pre_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;
@@ -818,18 +835,44 @@ static void blk_mq_rq_timed_out(struct request *req, bool reserved)
if (ops->timeout)
ret = ops->timeout(req, reserved);
+ if (ret == BLK_EH_RESET_TIMER)
+ blk_add_timer(req);
+
+ req->timeout_ret = ret;
+}
+
+static void blk_mq_rq_timed_out(struct request *req, bool reserved)
+{
+ enum blk_eh_timer_return ret = req->timeout_ret;
+ unsigned long flags;
+
switch (ret) {
case BLK_EH_HANDLED:
+ 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.
*/
+ spin_lock_irqsave(req->q->queue_lock, flags);
blk_mq_rq_update_aborted_gstate(req, 0);
- blk_add_timer(req);
+ if (blk_mq_rq_state(req) == MQ_RQ_COMPLETE_IN_TIMEOUT)
+ goto complete_rq;
+ spin_unlock_irqrestore(req->q->queue_lock, flags);
break;
case BLK_EH_NOT_HANDLED:
req->rq_flags |= RQF_MQ_TIMEOUT_EXPIRED;
@@ -875,7 +918,7 @@ static void blk_mq_check_expired(struct blk_mq_hw_ctx *hctx,
}
}
-static void blk_mq_terminate_expired(struct blk_mq_hw_ctx *hctx,
+static void blk_mq_prepare_expired(struct blk_mq_hw_ctx *hctx,
struct request *rq, void *priv, bool reserved)
{
/*
@@ -887,9 +930,40 @@ static void blk_mq_terminate_expired(struct blk_mq_hw_ctx *hctx,
*/
if (!(rq->rq_flags & RQF_MQ_TIMEOUT_EXPIRED) &&
READ_ONCE(rq->gstate) == rq->aborted_gstate)
+ blk_mq_rq_pre_timed_out(rq, reserved);
+}
+
+static void blk_mq_terminate_expired(struct blk_mq_hw_ctx *hctx,
+ struct request *rq, void *priv, bool reserved)
+{
+ if (!(rq->rq_flags & RQF_MQ_TIMEOUT_EXPIRED) &&
+ READ_ONCE(rq->gstate) == rq->aborted_gstate)
blk_mq_rq_timed_out(rq, reserved);
}
+static void blk_mq_timeout_synchronize_rcu(struct request_queue *q,
+ bool reset_expired)
+{
+ struct blk_mq_hw_ctx *hctx;
+ int i;
+ bool has_rcu = false;
+
+ queue_for_each_hw_ctx(q, hctx, i) {
+ if (!hctx->nr_expired)
+ continue;
+
+ if (!(hctx->flags & BLK_MQ_F_BLOCKING))
+ has_rcu = true;
+ else
+ synchronize_srcu(hctx->srcu);
+
+ if (reset_expired)
+ hctx->nr_expired = 0;
+ }
+ if (has_rcu)
+ synchronize_rcu();
+}
+
static void blk_mq_timeout_work(struct work_struct *work)
{
struct request_queue *q =
@@ -899,8 +973,6 @@ static void blk_mq_timeout_work(struct work_struct *work)
.next_set = 0,
.nr_expired = 0,
};
- struct blk_mq_hw_ctx *hctx;
- int i;
/* A deadlock might occur if a request is stuck requiring a
* timeout at the same time a queue freeze is waiting
@@ -922,27 +994,26 @@ static void blk_mq_timeout_work(struct work_struct *work)
blk_mq_queue_tag_busy_iter(q, blk_mq_check_expired, &data);
if (data.nr_expired) {
- bool has_rcu = false;
-
/*
* Wait till everyone sees ->aborted_gstate. The
* sequential waits for SRCUs aren't ideal. If this ever
* becomes a problem, we can add per-hw_ctx rcu_head and
* wait in parallel.
*/
- queue_for_each_hw_ctx(q, hctx, i) {
- if (!hctx->nr_expired)
- continue;
+ blk_mq_timeout_synchronize_rcu(q, false);
- if (!(hctx->flags & BLK_MQ_F_BLOCKING))
- has_rcu = true;
- else
- synchronize_srcu(hctx->srcu);
+ /* call .timeout() for timed-out requests */
+ blk_mq_queue_tag_busy_iter(q, blk_mq_prepare_expired, NULL);
- hctx->nr_expired = 0;
- }
- if (has_rcu)
- synchronize_rcu();
+ /*
+ * If .timeout returns BLK_EH_HANDLED, wait till current
+ * completion is done, for avoiding to update state on
+ * completed request.
+ *
+ * If .timeout returns BLK_EH_RESET_TIMER, wait till
+ * blk_add_timer() is commited before completing this rq.
+ */
+ blk_mq_timeout_synchronize_rcu(q, true);
/* terminate the ones we won */
blk_mq_queue_tag_busy_iter(q, blk_mq_terminate_expired, NULL);
@@ -952,6 +1023,9 @@ static void blk_mq_timeout_work(struct work_struct *work)
data.next = blk_rq_timeout(round_jiffies_up(data.next));
mod_timer(&q->timeout, data.next);
} else {
+ struct blk_mq_hw_ctx *hctx;
+ int i;
+
/*
* Request timeouts are handled as a forward rolling timer. If
* we end up here it means that no requests are pending and
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,
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 9af3e0f430bc..8278f67d39a6 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -252,8 +252,14 @@ struct request {
struct list_head timeout_list;
union {
+ /* used after completion */
struct __call_single_data csd;
+
+ /* used in io scheduler, before dispatch */
u64 fifo_time;
+
+ /* used after dispatch and before completion */
+ int timeout_ret;
};
/*
--
2.9.5