From: Yu Kuai <yukuai3@huawei.com>

commit cd5fc653381811f1e0ba65f5d169918cab61476f upstream.

There are two BUG reports that raid5 will hang at
bitmap_startwrite([1],[2]), root cause is that bitmap start write and end
write is unbalanced, it's not quite clear where, and while reviewing raid5
code, it's found that bitmap operations can be optimized. For example,
for a 4 disks raid5, with chunksize=8k, if user issue a IO (0 + 48k) to
the array:

┌────────────────────────────────────────────────────────────┐
│chunk 0                                                     │
│      ┌────────────┬─────────────┬─────────────┬────────────┼
│  sh0 │A0: 0 + 4k  │A1: 8k + 4k  │A2: 16k + 4k │A3: P       │
│      ┼────────────┼─────────────┼─────────────┼────────────┼
│  sh1 │B0: 4k + 4k │B1: 12k + 4k │B2: 20k + 4k │B3: P       │
┼──────┴────────────┴─────────────┴─────────────┴────────────┼
│chunk 1                                                     │
│      ┌────────────┬─────────────┬─────────────┬────────────┤
│  sh2 │C0: 24k + 4k│C1: 32k + 4k │C2: P        │C3: 40k + 4k│
│      ┼────────────┼─────────────┼─────────────┼────────────┼
│  sh3 │D0: 28k + 4k│D1: 36k + 4k │D2: P        │D3: 44k + 4k│
└──────┴────────────┴─────────────┴─────────────┴────────────┘

Before this patch, 4 stripe head will be used, and each sh will attach
bio for 3 disks, and each attached bio will trigger
bitmap_startwrite() once, which means total 12 times.
 - 3 times (0 + 4k), for (A0, A1 and A2)
 - 3 times (4 + 4k), for (B0, B1 and B2)
 - 3 times (8 + 4k), for (C0, C1 and C3)
 - 3 times (12 + 4k), for (D0, D1 and D3)

After this patch, md upper layer will calculate that IO range (0 + 48k)
is corresponding to the bitmap (0 + 16k), and call bitmap_startwrite()
just once.

Noted that this patch will align bitmap ranges to the chunks, for example,
if user issue a IO (0 + 4k) to array:

- Before this patch, 1 time (0 + 4k), for A0;
- After this patch, 1 time (0 + 8k) for chunk 0;

Usually, one bitmap bit will represent more than one disk chunk, and this
doesn't have any difference. And even if user really created a array
that one chunk contain multiple bits, the overhead is that more data
will be recovered after power failure.

Also remove STRIPE_BITMAP_PENDING since it's not used anymore.

[1] https://lore.kernel.org/all/CAJpMwyjmHQLvm6zg1cmQErttNNQPDAAXPKM3xgTjMhbfts986Q@mail.gmail.com/
[2] https://lore.kernel.org/all/ADF7D720-5764-4AF3-B68E-1845988737AA@flyingcircus.io/

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Link: https://lore.kernel.org/r/20250109015145.158868-6-yukuai1@huaweicloud.com
Signed-off-by: Song Liu <song@kernel.org>
---
 drivers/md/md-bitmap.c   |  2 --
 drivers/md/md.c          | 26 +++++++++++++++++++++
 drivers/md/md.h          |  2 ++
 drivers/md/raid1.c       |  5 ----
 drivers/md/raid10.c      |  4 ----
 drivers/md/raid5-cache.c |  2 --
 drivers/md/raid5.c       | 50 ++++------------------------------------
 drivers/md/raid5.h       |  3 ---
 8 files changed, 33 insertions(+), 61 deletions(-)

diff --git a/drivers/md/md-bitmap.c b/drivers/md/md-bitmap.c
index 1bb99102f7cc..2085b1705f14 100644
--- a/drivers/md/md-bitmap.c
+++ b/drivers/md/md-bitmap.c
@@ -1517,7 +1517,6 @@ int md_bitmap_startwrite(struct bitmap *bitmap, sector_t offset,
 	}
 	return 0;
 }
-EXPORT_SYMBOL_GPL(md_bitmap_startwrite);
 
 void md_bitmap_endwrite(struct bitmap *bitmap, sector_t offset,
 			unsigned long sectors)
@@ -1564,7 +1563,6 @@ void md_bitmap_endwrite(struct bitmap *bitmap, sector_t offset,
 			sectors = 0;
 	}
 }
-EXPORT_SYMBOL_GPL(md_bitmap_endwrite);
 
 static int __bitmap_start_sync(struct bitmap *bitmap, sector_t offset, sector_t *blocks,
 			       int degraded)
diff --git a/drivers/md/md.c b/drivers/md/md.c
index d1f6770c5cc0..9bc19a5a4119 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -8713,12 +8713,32 @@ void md_submit_discard_bio(struct mddev *mddev, struct md_rdev *rdev,
 }
 EXPORT_SYMBOL_GPL(md_submit_discard_bio);
 
+static void md_bitmap_start(struct mddev *mddev,
+			    struct md_io_clone *md_io_clone)
+{
+	if (mddev->pers->bitmap_sector)
+		mddev->pers->bitmap_sector(mddev, &md_io_clone->offset,
+					   &md_io_clone->sectors);
+
+	md_bitmap_startwrite(mddev->bitmap, md_io_clone->offset,
+			     md_io_clone->sectors);
+}
+
+static void md_bitmap_end(struct mddev *mddev, struct md_io_clone *md_io_clone)
+{
+	md_bitmap_endwrite(mddev->bitmap, md_io_clone->offset,
+			   md_io_clone->sectors);
+}
+
 static void md_end_clone_io(struct bio *bio)
 {
 	struct md_io_clone *md_io_clone = bio->bi_private;
 	struct bio *orig_bio = md_io_clone->orig_bio;
 	struct mddev *mddev = md_io_clone->mddev;
 
+	if (bio_data_dir(orig_bio) == WRITE && mddev->bitmap)
+		md_bitmap_end(mddev, md_io_clone);
+
 	if (bio->bi_status && !orig_bio->bi_status)
 		orig_bio->bi_status = bio->bi_status;
 
@@ -8743,6 +8763,12 @@ static void md_clone_bio(struct mddev *mddev, struct bio **bio)
 	if (blk_queue_io_stat(bdev->bd_disk->queue))
 		md_io_clone->start_time = bio_start_io_acct(*bio);
 
+	if (bio_data_dir(*bio) == WRITE && mddev->bitmap) {
+		md_io_clone->offset = (*bio)->bi_iter.bi_sector;
+		md_io_clone->sectors = bio_sectors(*bio);
+		md_bitmap_start(mddev, md_io_clone);
+	}
+
 	clone->bi_end_io = md_end_clone_io;
 	clone->bi_private = md_io_clone;
 	*bio = clone;
diff --git a/drivers/md/md.h b/drivers/md/md.h
index f395f4562bb9..f29fa8650cd0 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -746,6 +746,8 @@ struct md_io_clone {
 	struct mddev	*mddev;
 	struct bio	*orig_bio;
 	unsigned long	start_time;
+	sector_t	offset;
+	unsigned long	sectors;
 	struct bio	bio_clone;
 };
 
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index b5601acc810f..65309da1dca3 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -421,9 +421,6 @@ static void close_write(struct r1bio *r1_bio)
 	}
 	if (test_bit(R1BIO_BehindIO, &r1_bio->state))
 		md_bitmap_end_behind_write(r1_bio->mddev);
-	/* clear the bitmap if all writes complete successfully */
-	md_bitmap_endwrite(r1_bio->mddev->bitmap, r1_bio->sector,
-			   r1_bio->sectors);
 	md_write_end(r1_bio->mddev);
 }
 
@@ -1517,8 +1514,6 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
 
 			if (test_bit(R1BIO_BehindIO, &r1_bio->state))
 				md_bitmap_start_behind_write(mddev);
-			md_bitmap_startwrite(bitmap, r1_bio->sector,
-					     r1_bio->sectors);
 			first_clone = 0;
 		}
 
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 0b04ae46b52e..c300fd609ef0 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -427,9 +427,6 @@ static void raid10_end_read_request(struct bio *bio)
 
 static void close_write(struct r10bio *r10_bio)
 {
-	/* clear the bitmap if all writes complete successfully */
-	md_bitmap_endwrite(r10_bio->mddev->bitmap, r10_bio->sector,
-			   r10_bio->sectors);
 	md_write_end(r10_bio->mddev);
 }
 
@@ -1541,7 +1538,6 @@ static void raid10_write_request(struct mddev *mddev, struct bio *bio,
 	md_account_bio(mddev, &bio);
 	r10_bio->master_bio = bio;
 	atomic_set(&r10_bio->remaining, 1);
-	md_bitmap_startwrite(mddev->bitmap, r10_bio->sector, r10_bio->sectors);
 
 	for (i = 0; i < conf->copies; i++) {
 		if (r10_bio->devs[i].bio)
diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
index 8a0c8e78891f..53f3718c01eb 100644
--- a/drivers/md/raid5-cache.c
+++ b/drivers/md/raid5-cache.c
@@ -313,8 +313,6 @@ void r5c_handle_cached_data_endio(struct r5conf *conf,
 		if (sh->dev[i].written) {
 			set_bit(R5_UPTODATE, &sh->dev[i].flags);
 			r5c_return_dev_pending_writes(conf, &sh->dev[i]);
-			md_bitmap_endwrite(conf->mddev->bitmap, sh->sector,
-					   RAID5_STRIPE_SECTORS(conf));
 		}
 	}
 }
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 0918386bb8ea..f69e4a6a8a59 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -905,7 +905,6 @@ static bool stripe_can_batch(struct stripe_head *sh)
 	if (raid5_has_log(conf) || raid5_has_ppl(conf))
 		return false;
 	return test_bit(STRIPE_BATCH_READY, &sh->state) &&
-		!test_bit(STRIPE_BITMAP_PENDING, &sh->state) &&
 		is_full_stripe_write(sh);
 }
 
@@ -3587,29 +3586,9 @@ static void __add_stripe_bio(struct stripe_head *sh, struct bio *bi,
 		 (*bip)->bi_iter.bi_sector, sh->sector, dd_idx,
 		 sh->dev[dd_idx].sector);
 
-	if (conf->mddev->bitmap && firstwrite) {
-		/* Cannot hold spinlock over bitmap_startwrite,
-		 * but must ensure this isn't added to a batch until
-		 * we have added to the bitmap and set bm_seq.
-		 * So set STRIPE_BITMAP_PENDING to prevent
-		 * batching.
-		 * If multiple __add_stripe_bio() calls race here they
-		 * much all set STRIPE_BITMAP_PENDING.  So only the first one
-		 * to complete "bitmap_startwrite" gets to set
-		 * STRIPE_BIT_DELAY.  This is important as once a stripe
-		 * is added to a batch, STRIPE_BIT_DELAY cannot be changed
-		 * any more.
-		 */
-		set_bit(STRIPE_BITMAP_PENDING, &sh->state);
-		spin_unlock_irq(&sh->stripe_lock);
-		md_bitmap_startwrite(conf->mddev->bitmap, sh->sector,
-				     RAID5_STRIPE_SECTORS(conf));
-		spin_lock_irq(&sh->stripe_lock);
-		clear_bit(STRIPE_BITMAP_PENDING, &sh->state);
-		if (!sh->batch_head) {
-			sh->bm_seq = conf->seq_flush+1;
-			set_bit(STRIPE_BIT_DELAY, &sh->state);
-		}
+	if (conf->mddev->bitmap && firstwrite && !sh->batch_head) {
+		sh->bm_seq = conf->seq_flush+1;
+		set_bit(STRIPE_BIT_DELAY, &sh->state);
 	}
 }
 
@@ -3660,7 +3639,6 @@ handle_failed_stripe(struct r5conf *conf, struct stripe_head *sh,
 	BUG_ON(sh->batch_head);
 	for (i = disks; i--; ) {
 		struct bio *bi;
-		int bitmap_end = 0;
 
 		if (test_bit(R5_ReadError, &sh->dev[i].flags)) {
 			struct md_rdev *rdev;
@@ -3687,8 +3665,6 @@ handle_failed_stripe(struct r5conf *conf, struct stripe_head *sh,
 		sh->dev[i].towrite = NULL;
 		sh->overwrite_disks = 0;
 		spin_unlock_irq(&sh->stripe_lock);
-		if (bi)
-			bitmap_end = 1;
 
 		log_stripe_write_finished(sh);
 
@@ -3703,10 +3679,6 @@ handle_failed_stripe(struct r5conf *conf, struct stripe_head *sh,
 			bio_io_error(bi);
 			bi = nextbi;
 		}
-		if (bitmap_end)
-			md_bitmap_endwrite(conf->mddev->bitmap, sh->sector,
-					   RAID5_STRIPE_SECTORS(conf));
-		bitmap_end = 0;
 		/* and fail all 'written' */
 		bi = sh->dev[i].written;
 		sh->dev[i].written = NULL;
@@ -3715,7 +3687,6 @@ handle_failed_stripe(struct r5conf *conf, struct stripe_head *sh,
 			sh->dev[i].page = sh->dev[i].orig_page;
 		}
 
-		if (bi) bitmap_end = 1;
 		while (bi && bi->bi_iter.bi_sector <
 		       sh->dev[i].sector + RAID5_STRIPE_SECTORS(conf)) {
 			struct bio *bi2 = r5_next_bio(conf, bi, sh->dev[i].sector);
@@ -3749,9 +3720,6 @@ handle_failed_stripe(struct r5conf *conf, struct stripe_head *sh,
 				bi = nextbi;
 			}
 		}
-		if (bitmap_end)
-			md_bitmap_endwrite(conf->mddev->bitmap, sh->sector,
-					   RAID5_STRIPE_SECTORS(conf));
 		/* If we were in the middle of a write the parity block might
 		 * still be locked - so just clear all R5_LOCKED flags
 		 */
@@ -4102,8 +4070,7 @@ static void handle_stripe_clean_event(struct r5conf *conf,
 					bio_endio(wbi);
 					wbi = wbi2;
 				}
-				md_bitmap_endwrite(conf->mddev->bitmap, sh->sector,
-						   RAID5_STRIPE_SECTORS(conf));
+
 				if (head_sh->batch_head) {
 					sh = list_first_entry(&sh->batch_list,
 							      struct stripe_head,
@@ -4935,8 +4902,7 @@ static void break_stripe_batch_list(struct stripe_head *head_sh,
 					  (1 << STRIPE_COMPUTE_RUN)  |
 					  (1 << STRIPE_DISCARD) |
 					  (1 << STRIPE_BATCH_READY) |
-					  (1 << STRIPE_BATCH_ERR) |
-					  (1 << STRIPE_BITMAP_PENDING)),
+					  (1 << STRIPE_BATCH_ERR)),
 			"stripe state: %lx\n", sh->state);
 		WARN_ONCE(head_sh->state & ((1 << STRIPE_DISCARD) |
 					      (1 << STRIPE_REPLACED)),
@@ -5840,12 +5806,6 @@ static void make_discard_request(struct mddev *mddev, struct bio *bi)
 		}
 		spin_unlock_irq(&sh->stripe_lock);
 		if (conf->mddev->bitmap) {
-			for (d = 0;
-			     d < conf->raid_disks - conf->max_degraded;
-			     d++)
-				md_bitmap_startwrite(mddev->bitmap,
-						     sh->sector,
-						     RAID5_STRIPE_SECTORS(conf));
 			sh->bm_seq = conf->seq_flush + 1;
 			set_bit(STRIPE_BIT_DELAY, &sh->state);
 		}
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index 80948057b877..fd6171553880 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -371,9 +371,6 @@ enum {
 	STRIPE_ON_RELEASE_LIST,
 	STRIPE_BATCH_READY,
 	STRIPE_BATCH_ERR,
-	STRIPE_BITMAP_PENDING,	/* Being added to bitmap, don't add
-				 * to batch yet.
-				 */
 	STRIPE_LOG_TRAPPED,	/* trapped into log (see raid5-cache.c)
 				 * this bit is used in two scenarios:
 				 *
-- 
2.39.2