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Subject[PATCH 5/7] blk-mq: remove REQ_ATOM_COMPLETE usages from blk-mq
Date
After the recent updates to use generation number and state based
synchronization, blk-mq no longer depends on REQ_ATOM_COMPLETE except
to avoid firing the same timeout multiple times.

Remove all REQ_ATOM_COMPLETE usages and use a new rq_flags flag
RQF_MQ_TIMEOUT_EXPIRED to avoid firing the same timeout multiple
times. This removes atomic bitops from hot paths too.

v2: Removed blk_clear_rq_complete() from blk_mq_rq_timed_out().

v3: Added RQF_MQ_TIMEOUT_EXPIRED flag.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: "jianchao.wang" <jianchao.w.wang@oracle.com>
---
block/blk-mq.c | 18 ++++++++----------
block/blk-timeout.c | 1 +
include/linux/blkdev.h | 2 ++
3 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 88baa82..47e722b 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -607,14 +607,12 @@ void blk_mq_complete_request(struct request *rq)
*/
if (!(hctx->flags & BLK_MQ_F_BLOCKING)) {
rcu_read_lock();
- if (blk_mq_rq_aborted_gstate(rq) != rq->gstate &&
- !blk_mark_rq_complete(rq))
+ if (blk_mq_rq_aborted_gstate(rq) != rq->gstate)
__blk_mq_complete_request(rq);
rcu_read_unlock();
} else {
srcu_idx = srcu_read_lock(hctx->queue_rq_srcu);
- if (blk_mq_rq_aborted_gstate(rq) != rq->gstate &&
- !blk_mark_rq_complete(rq))
+ if (blk_mq_rq_aborted_gstate(rq) != rq->gstate)
__blk_mq_complete_request(rq);
srcu_read_unlock(hctx->queue_rq_srcu, srcu_idx);
}
@@ -665,8 +663,6 @@ void blk_mq_start_request(struct request *rq)
preempt_enable();

set_bit(REQ_ATOM_STARTED, &rq->atomic_flags);
- if (test_bit(REQ_ATOM_COMPLETE, &rq->atomic_flags))
- clear_bit(REQ_ATOM_COMPLETE, &rq->atomic_flags);

if (q->dma_drain_size && blk_rq_bytes(rq)) {
/*
@@ -817,6 +813,8 @@ static void blk_mq_rq_timed_out(struct request *req, bool reserved)
if (!test_bit(REQ_ATOM_STARTED, &req->atomic_flags))
return;

+ req->rq_flags |= RQF_MQ_TIMEOUT_EXPIRED;
+
if (ops->timeout)
ret = ops->timeout(req, reserved);

@@ -832,7 +830,6 @@ static void blk_mq_rq_timed_out(struct request *req, bool reserved)
*/
blk_mq_rq_update_aborted_gstate(req, 0);
blk_add_timer(req);
- blk_clear_rq_complete(req);
break;
case BLK_EH_NOT_HANDLED:
break;
@@ -851,7 +848,8 @@ static void blk_mq_check_expired(struct blk_mq_hw_ctx *hctx,

might_sleep();

- if (!test_bit(REQ_ATOM_STARTED, &rq->atomic_flags))
+ if ((rq->rq_flags & RQF_MQ_TIMEOUT_EXPIRED) ||
+ !test_bit(REQ_ATOM_STARTED, &rq->atomic_flags))
return;

/* read coherent snapshots of @rq->state_gen and @rq->deadline */
@@ -886,8 +884,8 @@ static void blk_mq_terminate_expired(struct blk_mq_hw_ctx *hctx,
* now guaranteed to see @rq->aborted_gstate and yield. If
* @rq->aborted_gstate still matches @rq->gstate, @rq is ours.
*/
- if (READ_ONCE(rq->gstate) == rq->aborted_gstate &&
- !blk_mark_rq_complete(rq))
+ if (!(rq->rq_flags & RQF_MQ_TIMEOUT_EXPIRED) &&
+ READ_ONCE(rq->gstate) == rq->aborted_gstate)
blk_mq_rq_timed_out(rq, reserved);
}

diff --git a/block/blk-timeout.c b/block/blk-timeout.c
index d580af3..25c4ffa 100644
--- a/block/blk-timeout.c
+++ b/block/blk-timeout.c
@@ -209,6 +209,7 @@ void blk_add_timer(struct request *req)
req->timeout = q->rq_timeout;

req->deadline = jiffies + req->timeout;
+ req->rq_flags &= ~RQF_MQ_TIMEOUT_EXPIRED;

/*
* Only the non-mq case needs to add the request to a protected list.
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 2d6fd11..13186a7 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -123,6 +123,8 @@ typedef __u32 __bitwise req_flags_t;
/* Look at ->special_vec for the actual data payload instead of the
bio chain. */
#define RQF_SPECIAL_PAYLOAD ((__force req_flags_t)(1 << 18))
+/* timeout is expired */
+#define RQF_MQ_TIMEOUT_EXPIRED ((__force req_flags_t)(1 << 19))

/* flags that prevent us from merging requests: */
#define RQF_NOMERGE_FLAGS \
--
2.9.5
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