[PATCH v3 7/8] md/raid10: skip futile retries on P2PDMA mapping failures

Same handling as the preceding raid1 commit: flag P2PDMA master
bios with R10BIO_P2PDMA at submission; on a BLK_STS_TARGET leg
failure retry writes once as a whole range, don't set
WantReplacement, block the leg for reads without charging the
read-error budget, don't trip FailFast.

Replacement legs keep the stock fail-on-write-error policy:
badblocks are never recorded on a replacement, so failing it is
the only outcome that cannot leave a silent hole in a rebuild.

Fixes: 02666132403a ("md: propagate BLK_FEAT_PCI_P2PDMA from member devices to RAID device")
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Mykola Marzhan <[email protected]>
---
 drivers/md/raid10.c | 63 ++++++++++++++++++++++++++++++++++-----------
 drivers/md/raid10.h |  2 ++
 2 files changed, 50 insertions(+), 15 deletions(-)

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index f7ef903a3d4e..4c3da50250a5 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -482,15 +482,23 @@ static void raid10_end_write_request(struct bio *bio)
 			 */
 			md_error(rdev->mddev, rdev);
 		else {
-			set_bit(WriteErrorSeen,	&rdev->flags);
-			if (!test_and_set_bit(WantReplacement, &rdev->flags))
-				set_bit(MD_RECOVERY_NEEDED,
-					&rdev->mddev->recovery);
+			/* Peer/member pairing failure, not member health. */
+			bool p2pdma_unmappable =
+				bio->bi_status == BLK_STS_TARGET &&
+				test_bit(R10BIO_P2PDMA, &r10_bio->state);
 
+			set_bit(WriteErrorSeen,	&rdev->flags);
 			dec_rdev = 0;
-			if (test_bit(FailFast, &rdev->flags) &&
-			    (bio->bi_opf & MD_FAILFAST)) {
-				md_error(rdev->mddev, rdev);
+			if (!p2pdma_unmappable) {
+				if (!test_and_set_bit(WantReplacement,
+						      &rdev->flags))
+					set_bit(MD_RECOVERY_NEEDED,
+						&rdev->mddev->recovery);
+
+				if (test_bit(FailFast, &rdev->flags) &&
+				    (bio->bi_opf & MD_FAILFAST)) {
+					md_error(rdev->mddev, rdev);
+				}
 			}
 
 			/*
@@ -1170,6 +1178,9 @@ static void raid10_read_request(struct mddev *mddev, struct bio *bio,
 	 */
 	gfp_t gfp = err_path ? (GFP_NOIO | __GFP_HIGH) : GFP_NOIO;
 
+	if (md_bio_is_p2pdma(bio))
+		set_bit(R10BIO_P2PDMA, &r10_bio->state);
+
 	if (slot >= 0 && r10_bio->devs[slot].rdev) {
 		/*
 		 * This is an error retry, but we cannot
@@ -1357,6 +1368,9 @@ static bool raid10_write_request(struct mddev *mddev, struct bio *bio,
 	sector_t sectors;
 	int max_sectors;
 
+	if (md_bio_is_p2pdma(bio))
+		set_bit(R10BIO_P2PDMA, &r10_bio->state);
+
 	if ((mddev_is_clustered(mddev) &&
 	     mddev->cluster_ops->area_resyncing(mddev, WRITE,
 						bio->bi_iter.bi_sector,
@@ -2786,7 +2800,7 @@ static void fix_read_error(struct r10conf *conf, struct mddev *mddev, struct r10
 	}
 }
 
-static void narrow_write_error(struct r10bio *r10_bio, int i)
+static void narrow_write_error(struct r10bio *r10_bio, int i, bool coarse)
 {
 	struct bio *bio = r10_bio->master_bio;
 	struct mddev *mddev = r10_bio->mddev;
@@ -2800,6 +2814,9 @@ static void narrow_write_error(struct r10bio *r10_bio, int i)
 	 * It is conceivable that the bio doesn't exactly align with
 	 * blocks.  We must handle this.
 	 *
+	 * With 'coarse', retry the whole range as one bio: P2PDMA
+	 * mapping failures fail every block identically.
+	 *
 	 * We currently own a reference to the rdev.
 	 */
 
@@ -2814,9 +2831,12 @@ static void narrow_write_error(struct r10bio *r10_bio, int i)
 		block_sectors = roundup(1 << rdev->badblocks.shift, lbs);
 
 	sector = r10_bio->sector;
-	sectors = ((r10_bio->sector + block_sectors)
-		   & ~(sector_t)(block_sectors - 1))
-		- sector;
+	if (coarse)
+		sectors = sect_to_write;
+	else
+		sectors = ((r10_bio->sector + block_sectors)
+			   & ~(sector_t)(block_sectors - 1))
+			- sector;
 
 	while (sect_to_write) {
 		struct bio *wbio;
@@ -2856,6 +2876,7 @@ static void handle_read_error(struct mddev *mddev, struct r10bio *r10_bio)
 {
 	int slot = r10_bio->read_slot;
 	struct bio *bio;
+	bool p2pdma_error;
 	struct r10conf *conf = mddev->private;
 	struct md_rdev *rdev = r10_bio->devs[slot].rdev;
 
@@ -2868,17 +2889,24 @@ static void handle_read_error(struct mddev *mddev, struct r10bio *r10_bio)
 	 * frozen.
 	 */
 	bio = r10_bio->devs[slot].bio;
+	/* evaluate before the bio_put() below */
+	p2pdma_error = bio->bi_status == BLK_STS_TARGET &&
+		test_bit(R10BIO_P2PDMA, &r10_bio->state);
 	bio_put(bio);
 	r10_bio->devs[slot].bio = NULL;
 
 	if (mddev->ro)
 		r10_bio->devs[slot].bio = IO_BLOCKED;
-	else if (!test_bit(FailFast, &rdev->flags)) {
+	else if (p2pdma_error) {
+		/* Peer can't reach this member: just redirect the read. */
+		r10_bio->devs[slot].bio = IO_BLOCKED;
+	} else if (test_bit(FailFast, &rdev->flags)) {
+		md_error(mddev, rdev);
+	} else {
 		freeze_array(conf, 1);
 		fix_read_error(conf, mddev, r10_bio);
 		unfreeze_array(conf);
-	} else
-		md_error(mddev, rdev);
+	}
 
 	rdev_dec_pending(rdev, mddev);
 	r10_bio->state = 0;
@@ -2947,8 +2975,13 @@ static void handle_write_completed(struct r10conf *conf, struct r10bio *r10_bio)
 					r10_bio->sectors, 0);
 				rdev_dec_pending(rdev, conf->mddev);
 			} else if (bio != NULL && bio->bi_status) {
+				bool coarse = bio->bi_status ==
+						BLK_STS_TARGET &&
+					test_bit(R10BIO_P2PDMA,
+						 &r10_bio->state);
+
 				fail = true;
-				narrow_write_error(r10_bio, m);
+				narrow_write_error(r10_bio, m, coarse);
 				rdev_dec_pending(rdev, conf->mddev);
 			}
 			bio = r10_bio->devs[m].repl_bio;
diff --git a/drivers/md/raid10.h b/drivers/md/raid10.h
index ec79d87fb92f..a2e1554f77db 100644
--- a/drivers/md/raid10.h
+++ b/drivers/md/raid10.h
@@ -174,6 +174,8 @@ enum r10bio_state {
 	R10BIO_Previous,
 /* failfast devices did receive failfast requests. */
 	R10BIO_FailFast,
+/* the master bio carries PCI P2PDMA (peer device memory) pages */
+	R10BIO_P2PDMA,
 	R10BIO_Discard,
 };
 #endif
-- 
2.52.0