[PATCH v6 04/12] md/raid1: don't use write-behind for P2PDMA bios
Mykola Marzhan <[email protected]>
| Newsgroups | org.kernel.vger.linux-block,org.infradead.lists.linux-nvme,org.kernel.vger.linux-kernel,org.kernel.vger.linux-pci,org.kernel.vger.linux-raid,org.kernel.vger.linux-rdma,org.kernel.vger.stable |
|---|---|
| Message-ID | <[email protected]> |
alloc_behind_master_bio() copies the bio's data with bio_copy_data(),
a CPU copy. P2PDMA pages are peer device (BAR) memory; generic code
must not assume CPU load/store access to them is safe or fast on
every architecture, and bouncing peer memory through the CPU defeats
the point of a peer-to-peer transfer.
Skip write-behind for P2PDMA bios: they are written directly to all
members, including write-mostly ones. Ordering against write-behind
I/O in flight to overlapping sectors is preserved: the non-behind
clone path serializes on CollisionCheck rdevs (see the preceding
fix), which covers these bios like any other write that bypasses
write-behind.
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]>
Reviewed-by: Logan Gunthorpe <[email protected]>
---
drivers/md/raid1.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 997f79c05db7..7d769b6460ca 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -1523,6 +1523,7 @@ static bool raid1_write_request(struct mddev *mddev, struct bio *bio,
bool write_behind = false;
bool nowait = bio->bi_opf & REQ_NOWAIT;
bool is_discard = op_is_discard(bio->bi_opf);
+ bool is_p2pdma = md_bio_is_p2pdma(bio);
sector_t sector = bio->bi_iter.bi_sector;
if (mddev_is_clustered(mddev) &&
@@ -1575,9 +1576,12 @@ static bool raid1_write_request(struct mddev *mddev, struct bio *bio,
/*
* The write-behind io is only attempted on drives marked as
* write-mostly, which means we could allocate write behind
- * bio later.
+ * bio later. P2PDMA bios are excluded: write-behind copies
+ * the data with bio_copy_data(), a CPU copy that cannot be
+ * assumed safe or fast on P2PDMA (device BAR) pages.
*/
- if (!is_discard && rdev && test_bit(WriteMostly, &rdev->flags))
+ if (!is_discard && !is_p2pdma && rdev &&
+ test_bit(WriteMostly, &rdev->flags))
write_behind = true;
r1_bio->bios[i] = NULL;
--
2.52.0