Revert "blk-mq: put driver tag when this request is completed"

This reverts commits the following commits:

	37f4a24c
	723bf178
	36a3df5a

The last one is the culprit, but we have to go a bit deeper to get this
to revert cleanly. There's been a report that this breaks some MMC
setups [1], and also causes an issue with swap [2]. Until this can be
figured out, revert the offending commits.

[1] https://lore.kernel.org/linux-block/57fb09b1-54ba-f3aa-f82c-d709b0e6b281@samsung.com/
[2] https://lore.kernel.org/linux-block/20200702043721.GA1087@lca.pw/Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reported-by: Qian Cai <cai@lca.pw>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-flush.c

@@ -236,10 +236,13 @@ static void flush_end_io(struct request *flush_rq, blk_status_t error)
 		error = fq->rq_status;
 
 	hctx = flush_rq->mq_hctx;
-	if (!q->elevator)
-		flush_rq->tag = BLK_MQ_NO_TAG;
-	else
-		flush_rq->internal_tag = BLK_MQ_NO_TAG;
+	if (!q->elevator) {
+		blk_mq_tag_set_rq(hctx, flush_rq->tag, fq->orig_rq);
+		flush_rq->tag = -1;
+	} else {
+		blk_mq_put_driver_tag(flush_rq);
+		flush_rq->internal_tag = -1;
+	}
 
 	running = &fq->flush_queue[fq->flush_running_idx];
 	BUG_ON(fq->flush_pending_idx == fq->flush_running_idx);
@@ -313,10 +316,13 @@ static void blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq,
 	flush_rq->mq_ctx = first_rq->mq_ctx;
 	flush_rq->mq_hctx = first_rq->mq_hctx;
 
-	if (!q->elevator)
+	if (!q->elevator) {
+		fq->orig_rq = first_rq;
 		flush_rq->tag = first_rq->tag;
-	else
+		blk_mq_tag_set_rq(flush_rq->mq_hctx, first_rq->tag, flush_rq);
+	} else {
 		flush_rq->internal_tag = first_rq->internal_tag;
+	}
 
 	flush_rq->cmd_flags = REQ_OP_FLUSH | REQ_PREFLUSH;
 	flush_rq->cmd_flags |= (flags & REQ_DRV) | (flags & REQ_FAILFAST_MASK);
@@ -335,6 +341,11 @@ static void mq_flush_data_end_io(struct request *rq, blk_status_t error)
 	unsigned long flags;
 	struct blk_flush_queue *fq = blk_get_flush_queue(q, ctx);
 
+	if (q->elevator) {
+		WARN_ON(rq->tag < 0);
+		blk_mq_put_driver_tag(rq);
+	}
+
 	/*
 	 * After populating an empty queue, kick it to avoid stall.  Read
 	 * the comment in flush_end_io().

block/blk-mq-tag.h

@@ -101,6 +101,18 @@ static inline bool hctx_may_queue(struct blk_mq_hw_ctx *hctx,
 	return atomic_read(&hctx->nr_active) < depth;
 }
 
+/*
+ * This helper should only be used for flush request to share tag
+ * with the request cloned from, and both the two requests can't be
+ * in flight at the same time. The caller has to make sure the tag
+ * can't be freed.
+ */
+static inline void blk_mq_tag_set_rq(struct blk_mq_hw_ctx *hctx,
+		unsigned int tag, struct request *rq)
+{
+	hctx->tags->rqs[tag] = rq;
+}
+
 static inline bool blk_mq_tag_is_reserved(struct blk_mq_tags *tags,
 					  unsigned int tag)
 {

block/blk-mq.c

@@ -277,20 +277,26 @@ static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data,
 {
 	struct blk_mq_tags *tags = blk_mq_tags_from_data(data);
 	struct request *rq = tags->static_rqs[tag];
+	req_flags_t rq_flags = 0;
 
 	if (data->q->elevator) {
 		rq->tag = BLK_MQ_NO_TAG;
 		rq->internal_tag = tag;
 	} else {
+		if (data->hctx->flags & BLK_MQ_F_TAG_SHARED) {
+			rq_flags = RQF_MQ_INFLIGHT;
+			atomic_inc(&data->hctx->nr_active);
+		}
 		rq->tag = tag;
 		rq->internal_tag = BLK_MQ_NO_TAG;
+		data->hctx->tags->rqs[rq->tag] = rq;
 	}
 
 	/* csd/requeue_work/fifo_time is initialized before use */
 	rq->q = data->q;
 	rq->mq_ctx = data->ctx;
 	rq->mq_hctx = data->hctx;
-	rq->rq_flags = 0;
+	rq->rq_flags = rq_flags;
 	rq->cmd_flags = data->cmd_flags;
 	if (data->flags & BLK_MQ_REQ_PREEMPT)
 		rq->rq_flags |= RQF_PREEMPT;
@@ -660,32 +666,10 @@ static inline bool blk_mq_complete_need_ipi(struct request *rq)
 	return cpu_online(rq->mq_ctx->cpu);
 }
 
-static void __blk_mq_put_driver_tag(struct blk_mq_hw_ctx *hctx,
-		struct request *rq)
-{
-	blk_mq_put_tag(hctx->tags, rq->mq_ctx, rq->tag);
-	rq->tag = BLK_MQ_NO_TAG;
-
-	if (rq->rq_flags & RQF_MQ_INFLIGHT) {
-		rq->rq_flags &= ~RQF_MQ_INFLIGHT;
-		atomic_dec(&hctx->nr_active);
-	}
-}
-
-static inline void blk_mq_put_driver_tag(struct request *rq)
-{
-	if (rq->tag == BLK_MQ_NO_TAG || rq->internal_tag == BLK_MQ_NO_TAG)
-		return;
-
-	__blk_mq_put_driver_tag(rq->mq_hctx, rq);
-}
-
 bool blk_mq_complete_request_remote(struct request *rq)
 {
 	WRITE_ONCE(rq->state, MQ_RQ_COMPLETE);
 
-	blk_mq_put_driver_tag(rq);
-
 	/*
 	 * For a polled request, always complete locallly, it's pointless
 	 * to redirect the completion.
@@ -1121,10 +1105,9 @@ static bool __blk_mq_get_driver_tag(struct request *rq)
 {
 	struct sbitmap_queue *bt = &rq->mq_hctx->tags->bitmap_tags;
 	unsigned int tag_offset = rq->mq_hctx->tags->nr_reserved_tags;
+	bool shared = blk_mq_tag_busy(rq->mq_hctx);
 	int tag;
 
-	blk_mq_tag_busy(rq->mq_hctx);
-
 	if (blk_mq_tag_is_reserved(rq->mq_hctx->sched_tags, rq->internal_tag)) {
 		bt = &rq->mq_hctx->tags->breserved_tags;
 		tag_offset = 0;
@@ -1137,22 +1120,19 @@ static bool __blk_mq_get_driver_tag(struct request *rq)
 		return false;
 
 	rq->tag = tag + tag_offset;
+	if (shared) {
+		rq->rq_flags |= RQF_MQ_INFLIGHT;
+		atomic_inc(&rq->mq_hctx->nr_active);
+	}
+	rq->mq_hctx->tags->rqs[rq->tag] = rq;
 	return true;
 }
 
 static bool blk_mq_get_driver_tag(struct request *rq)
 {
-	struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
-
-	if (rq->tag == BLK_MQ_NO_TAG && !__blk_mq_get_driver_tag(rq))
-		return false;
-
-	if (hctx->flags & BLK_MQ_F_TAG_SHARED) {
-		rq->rq_flags |= RQF_MQ_INFLIGHT;
-		atomic_inc(&hctx->nr_active);
-	}
-	hctx->tags->rqs[rq->tag] = rq;
-	return true;
+	if (rq->tag != BLK_MQ_NO_TAG)
+		return true;
+	return __blk_mq_get_driver_tag(rq);
 }
 
 static int blk_mq_dispatch_wake(wait_queue_entry_t *wait, unsigned mode,

block/blk-mq.h

@@ -193,6 +193,26 @@ static inline bool blk_mq_get_dispatch_budget(struct request_queue *q)
 	return true;
 }
 
+static inline void __blk_mq_put_driver_tag(struct blk_mq_hw_ctx *hctx,
+					   struct request *rq)
+{
+	blk_mq_put_tag(hctx->tags, rq->mq_ctx, rq->tag);
+	rq->tag = BLK_MQ_NO_TAG;
+
+	if (rq->rq_flags & RQF_MQ_INFLIGHT) {
+		rq->rq_flags &= ~RQF_MQ_INFLIGHT;
+		atomic_dec(&hctx->nr_active);
+	}
+}
+
+static inline void blk_mq_put_driver_tag(struct request *rq)
+{
+	if (rq->tag == BLK_MQ_NO_TAG || rq->internal_tag == BLK_MQ_NO_TAG)
+		return;
+
+	__blk_mq_put_driver_tag(rq->mq_hctx, rq);
+}
+
 static inline void blk_mq_clear_mq_map(struct blk_mq_queue_map *qmap)
 {
 	int cpu;

block/blk.h

@@ -25,6 +25,11 @@ struct blk_flush_queue {
 	struct list_head	flush_data_in_flight;
 	struct request		*flush_rq;
 
+	/*
+	 * flush_rq shares tag with this rq, both can't be active
+	 * at the same time
+	 */
+	struct request		*orig_rq;
 	struct lock_class_key	key;
 	spinlock_t		mq_flush_lock;
 };