[PATCH 3/6] md/raid1: don't use write-behind for P2PDMA bios
Mykola Marzhan <[email protected]>
| Newsgroups | gmane.linux.kernel.pci,gmane.linux.block,gmane.linux.raid,gmane.linux.kernel,gmane.linux.drivers.rdma |
|---|---|
| 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.
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/raid1.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index afe2ca96ad8c..57f64e890102 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -1575,9 +1575,12 @@ 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 && rdev && test_bit(WriteMostly, &rdev->flags) &&
+ !md_bio_is_p2pdma(bio))
write_behind = true;
r1_bio->bios[i] = NULL;
--
2.43.0