2023-07-07 10:11:47

by Chengming Zhou

Subject: [PATCH v3 4/4] blk-flush: reuse rq queuelist in flush state machine

From: Chengming Zhou <[email protected]>

Since we don't need to maintain inflight flush_data requests list
anymore, we can reuse rq->queuelist for flush pending list.

Note in mq_flush_data_end_io(), we need to re-initialize rq->queuelist
before reusing it in the state machine when end, since the rq->rq_next
also reuse it, may have corrupted rq->queuelist by the driver.

This patch decrease the size of struct request by 16 bytes.

Signed-off-by: Chengming Zhou <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
---
v3:
- fix a bug report of blktests nvme/012, we need to re-initialize
rq->queuelist before reusing it in the state machine when end.
Because rq->rq_next reuse may have corrupted it. Thanks Ming Lei.
---
block/blk-flush.c | 17 ++++++++++-------
include/linux/blk-mq.h | 1 -
2 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/block/blk-flush.c b/block/blk-flush.c
index bb7adfc2a5da..4826d2d61a23 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -183,14 +183,13 @@ static void blk_flush_complete_seq(struct request *rq,
/* queue for flush */
if (list_empty(pending))
fq->flush_pending_since = jiffies;
- list_move_tail(&rq->flush.list, pending);
+ list_move_tail(&rq->queuelist, pending);
break;

case REQ_FSEQ_DATA:
- list_del_init(&rq->flush.list);
fq->flush_data_in_flight++;
spin_lock(&q->requeue_lock);
- list_add_tail(&rq->queuelist, &q->flush_list);
+ list_move_tail(&rq->queuelist, &q->flush_list);
spin_unlock(&q->requeue_lock);
blk_mq_kick_requeue_list(q);
break;
@@ -202,7 +201,7 @@ static void blk_flush_complete_seq(struct request *rq,
* flush data request completion path. Restore @rq for
* normal completion and end it.
*/
- list_del_init(&rq->flush.list);
+ list_del_init(&rq->queuelist);
blk_flush_restore_request(rq);
blk_mq_end_request(rq, error);
break;
@@ -258,7 +257,7 @@ static enum rq_end_io_ret flush_end_io(struct request *flush_rq,
fq->flush_running_idx ^= 1;

/* and push the waiting requests to the next stage */
- list_for_each_entry_safe(rq, n, running, flush.list) {
+ list_for_each_entry_safe(rq, n, running, queuelist) {
unsigned int seq = blk_flush_cur_seq(rq);

BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
@@ -292,7 +291,7 @@ static void blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq,
{
struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
struct request *first_rq =
- list_first_entry(pending, struct request, flush.list);
+ list_first_entry(pending, struct request, queuelist);
struct request *flush_rq = fq->flush_rq;

/* C1 described at the top of this file */
@@ -376,6 +375,11 @@ static enum rq_end_io_ret mq_flush_data_end_io(struct request *rq,
*/
spin_lock_irqsave(&fq->mq_flush_lock, flags);
fq->flush_data_in_flight--;
+ /*
+ * May have been corrupted by rq->rq_next reuse, we need to
+ * re-initialize rq->queuelist before reusing it here.
+ */
+ INIT_LIST_HEAD(&rq->queuelist);
blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error);
spin_unlock_irqrestore(&fq->mq_flush_lock, flags);

@@ -386,7 +390,6 @@ static enum rq_end_io_ret mq_flush_data_end_io(struct request *rq,
static void blk_rq_init_flush(struct request *rq)
{
rq->flush.seq = 0;
- INIT_LIST_HEAD(&rq->flush.list);
rq->rq_flags |= RQF_FLUSH_SEQ;
rq->flush.saved_end_io = rq->end_io; /* Usually NULL */
rq->end_io = mq_flush_data_end_io;
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 34d400171b3e..ab790eba5fcf 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -176,7 +176,6 @@ struct request {

struct {
unsigned int seq;
- struct list_head list;
rq_end_io_fn *saved_end_io;
} flush;

--
2.41.0

2023-07-07 10:31:39

by Ming Lei

Subject: Re: [PATCH v3 4/4] blk-flush: reuse rq queuelist in flush state machine

On Fri, Jul 07, 2023 at 05:37:22PM +0800, [email protected] wrote:
> From: Chengming Zhou <[email protected]>
>
> Since we don't need to maintain inflight flush_data requests list
> anymore, we can reuse rq->queuelist for flush pending list.
>
> Note in mq_flush_data_end_io(), we need to re-initialize rq->queuelist
> before reusing it in the state machine when end, since the rq->rq_next
> also reuse it, may have corrupted rq->queuelist by the driver.
>
> This patch decrease the size of struct request by 16 bytes.
>
> Signed-off-by: Chengming Zhou <[email protected]>
> Reviewed-by: Christoph Hellwig <[email protected]>
> ---
> v3:
> - fix a bug report of blktests nvme/012, we need to re-initialize
> rq->queuelist before reusing it in the state machine when end.
> Because rq->rq_next reuse may have corrupted it. Thanks Ming Lei.

Reviewed-by: Ming Lei <[email protected]>

Thanks,
Ming