linux-kernel - [PATCH v5 09/16] md/raid10: fix failfast read error not rescheduled

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Message-ID: <20251027150433.18193-10-k@mgml.me>
Date: Tue, 28 Oct 2025 00:04:26 +0900
From: Kenta Akagi <k@...l.me>
To: Song Liu <song@...nel.org>, Yu Kuai <yukuai@...as.com>,
        Shaohua Li <shli@...com>, Mariusz Tkaczyk <mtkaczyk@...nel.org>,
        Guoqing Jiang <jgq516@...il.com>
Cc: linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org,
        Kenta Akagi <k@...l.me>, Li Nan <linan122@...wei.com>
Subject: [PATCH v5 09/16] md/raid10: fix failfast read error not rescheduled

raid10_end_read_request lacks a path to retry when a FailFast IO fails.
As a result, when Failfast Read IOs fail on all rdevs, the upper layer
receives EIO, without read rescheduled.

Looking at the two commits below, it seems only raid10_end_read_request
lacks the failfast read retry handling, while raid1_end_read_request has
it. In RAID1, the retry works as expected.
* commit 8d3ca83dcf9c ("md/raid10: add failfast handling for reads.")
* commit 2e52d449bcec ("md/raid1: add failfast handling for reads.")

This commit will make the failfast read bio for the last rdev in raid10
retry if it fails.

Fixes: 8d3ca83dcf9c ("md/raid10: add failfast handling for reads.")
Signed-off-by: Kenta Akagi <k@...l.me>
Reviewed-by: Li Nan <linan122@...wei.com>
---
 drivers/md/raid10.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 87468113e31a..1dd27b9ef48e 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -401,6 +401,13 @@ static void raid10_end_read_request(struct bio *bio)
 		 * wait for the 'master' bio.
 		 */
 		set_bit(R10BIO_Uptodate, &r10_bio->state);
+	} else if (test_bit(FailFast, &rdev->flags) &&
+		 test_bit(R10BIO_FailFast, &r10_bio->state)) {
+		/*
+		 * This was a fail-fast read so we definitely
+		 * want to retry
+		 */
+		;
 	} else if (!raid1_should_handle_error(bio)) {
 		uptodate = 1;
 	} else {
-- 
2.50.1