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Message-ID: <CALTww28uPhB1R5xumS7MwEqE-S0C1MKET+2mEsC_nvdgrvJJsg@mail.gmail.com>
Date: Wed, 19 Nov 2025 11:22:00 +0800
From: Xiao Ni <xni@...hat.com>
To: Kenta Akagi <k@...l.me>
Cc: Song Liu <song@...nel.org>, Yu Kuai <yukuai3@...wei.com>,
Mariusz Tkaczyk <mtkaczyk@...nel.org>, Guoqing Jiang <jgq516@...il.com>, linux-raid@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/3] md/raid1,raid10: Do not set MD_BROKEN on failfast
io failure
Hi Kenta
Re-send the email because I received the reject email from
linux-raid/linux-kernel.
I know the patch set is already V5 now. I'm looking at all the emails
to understand the evolution process. Because v5 is much more
complicated than the original version. I understand the problem
already. We don't want to set MD_BROKEN for failfast normal/metadata
io. Can't it work that check FailFast before setting MD_BROKEN, such
as:
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 202e510f73a4..7acac7eef514 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -1755,12 +1755,13 @@ static void raid1_error(struct mddev *mddev,
struct md_rdev *rdev)
if (test_bit(In_sync, &rdev->flags) &&
(conf->raid_disks - mddev->degraded) == 1) {
- set_bit(MD_BROKEN, &mddev->flags);
- if (!mddev->fail_last_dev) {
+ if (!mddev->fail_last_dev || test_bit(FailFast, &rdev->flags)) {
conf->recovery_disabled = mddev->recovery_disabled;
return;
}
+
+ set_bit(MD_BROKEN, &mddev->flags);
}
set_bit(Blocked, &rdev->flags);
if (test_and_clear_bit(In_sync, &rdev->flags))
I know mostly this way can't resolve this problem. Because you, Linan
and Kuai already talked a lot about this problem. But I don't know why
this change can't work.
Regards
Xiao
On Fri, Aug 29, 2025 at 12:39 AM Kenta Akagi <k@...l.me> wrote:
>
> This commit ensures that an MD_FAILFAST IO failure does not put
> the array into a broken state.
>
> When failfast is enabled on rdev in RAID1 or RAID10,
> the array may be flagged MD_BROKEN in the following cases.
> - If MD_FAILFAST IOs to multiple rdevs fail simultaneously
> - If an MD_FAILFAST metadata write to the 'last' rdev fails
>
> The MD_FAILFAST bio error handler always calls md_error on IO failure,
> under the assumption that raid{1,10}_error will neither fail
> the last rdev nor break the array.
> After commit 9631abdbf406 ("md: Set MD_BROKEN for RAID1 and RAID10"),
> calling md_error on the 'last' rdev in RAID1/10 always sets
> the MD_BROKEN flag on the array.
> As a result, when failfast IO fails on the last rdev, the array
> immediately becomes failed.
>
> Normally, MD_FAILFAST IOs are not issued to the 'last' rdev, so this is
> an edge case; however, it can occur if rdevs in a non-degraded
> array share the same path and that path is lost, or if a metadata
> write is triggered in a degraded array and fails due to failfast.
>
> When a failfast metadata write fails, it is retried through the
> following sequence. If a metadata write without failfast fails,
> the array will be marked with MD_BROKEN.
>
> 1. MD_SB_NEED_REWRITE is set in sb_flags by super_written.
> 2. md_super_wait, called by the function executing md_super_write,
> returns -EAGAIN due to MD_SB_NEED_REWRITE.
> 3. The caller of md_super_wait (e.g., md_update_sb) receives the
> negative return value and retries md_super_write.
> 4. md_super_write issues the metadata write again,
> this time without MD_FAILFAST.
>
> Fixes: 9631abdbf406 ("md: Set MD_BROKEN for RAID1 and RAID10")
> Signed-off-by: Kenta Akagi <k@...l.me>
> ---
> drivers/md/md.c | 14 +++++++++-----
> drivers/md/md.h | 13 +++++++------
> drivers/md/raid1.c | 18 ++++++++++++++++--
> drivers/md/raid10.c | 21 ++++++++++++++++++---
> 4 files changed, 50 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index ac85ec73a409..547b88e253f7 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -999,14 +999,18 @@ static void super_written(struct bio *bio)
> if (bio->bi_status) {
> pr_err("md: %s gets error=%d\n", __func__,
> blk_status_to_errno(bio->bi_status));
> + if (bio->bi_opf & MD_FAILFAST)
> + set_bit(FailfastIOFailure, &rdev->flags);
> md_error(mddev, rdev);
> if (!test_bit(Faulty, &rdev->flags)
> && (bio->bi_opf & MD_FAILFAST)) {
> + pr_warn("md: %s: Metadata write will be repeated to %pg\n",
> + mdname(mddev), rdev->bdev);
> set_bit(MD_SB_NEED_REWRITE, &mddev->sb_flags);
> - set_bit(LastDev, &rdev->flags);
> }
> - } else
> - clear_bit(LastDev, &rdev->flags);
> + } else {
> + clear_bit(MD_SB_NEED_REWRITE, &mddev->sb_flags);
> + }
>
> bio_put(bio);
>
> @@ -1048,7 +1052,7 @@ void md_super_write(struct mddev *mddev, struct md_rdev *rdev,
>
> if (test_bit(MD_FAILFAST_SUPPORTED, &mddev->flags) &&
> test_bit(FailFast, &rdev->flags) &&
> - !test_bit(LastDev, &rdev->flags))
> + !test_bit(MD_SB_NEED_REWRITE, &mddev->sb_flags))
> bio->bi_opf |= MD_FAILFAST;
>
> atomic_inc(&mddev->pending_writes);
> @@ -1059,7 +1063,7 @@ int md_super_wait(struct mddev *mddev)
> {
> /* wait for all superblock writes that were scheduled to complete */
> wait_event(mddev->sb_wait, atomic_read(&mddev->pending_writes)==0);
> - if (test_and_clear_bit(MD_SB_NEED_REWRITE, &mddev->sb_flags))
> + if (test_bit(MD_SB_NEED_REWRITE, &mddev->sb_flags))
> return -EAGAIN;
> return 0;
> }
> diff --git a/drivers/md/md.h b/drivers/md/md.h
> index 51af29a03079..52c9fc759015 100644
> --- a/drivers/md/md.h
> +++ b/drivers/md/md.h
> @@ -281,9 +281,10 @@ enum flag_bits {
> * It is expects that no bad block log
> * is present.
> */
> - LastDev, /* Seems to be the last working dev as
> - * it didn't fail, so don't use FailFast
> - * any more for metadata
> + FailfastIOFailure, /* rdev with failfast IO failure
> + * but md_error not yet completed.
> + * If the last rdev has this flag,
> + * error_handler must not fail the array
> */
> CollisionCheck, /*
> * check if there is collision between raid1
> @@ -331,8 +332,8 @@ struct md_cluster_operations;
> * @MD_CLUSTER_RESYNC_LOCKED: cluster raid only, which means node, already took
> * resync lock, need to release the lock.
> * @MD_FAILFAST_SUPPORTED: Using MD_FAILFAST on metadata writes is supported as
> - * calls to md_error() will never cause the array to
> - * become failed.
> + * calls to md_error() with FailfastIOFailure will
> + * never cause the array to become failed.
> * @MD_HAS_PPL: The raid array has PPL feature set.
> * @MD_HAS_MULTIPLE_PPLS: The raid array has multiple PPLs feature set.
> * @MD_NOT_READY: do_md_run() is active, so 'array_state', ust not report that
> @@ -360,7 +361,7 @@ enum mddev_sb_flags {
> MD_SB_CHANGE_DEVS, /* Some device status has changed */
> MD_SB_CHANGE_CLEAN, /* transition to or from 'clean' */
> MD_SB_CHANGE_PENDING, /* switch from 'clean' to 'active' in progress */
> - MD_SB_NEED_REWRITE, /* metadata write needs to be repeated */
> + MD_SB_NEED_REWRITE, /* metadata write needs to be repeated, do not use failfast */
> };
>
> #define NR_SERIAL_INFOS 8
> diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
> index 408c26398321..8a61fd93b3ff 100644
> --- a/drivers/md/raid1.c
> +++ b/drivers/md/raid1.c
> @@ -470,6 +470,7 @@ static void raid1_end_write_request(struct bio *bio)
> (bio->bi_opf & MD_FAILFAST) &&
> /* We never try FailFast to WriteMostly devices */
> !test_bit(WriteMostly, &rdev->flags)) {
> + set_bit(FailfastIOFailure, &rdev->flags);
> md_error(r1_bio->mddev, rdev);
> }
>
> @@ -1746,8 +1747,12 @@ static void raid1_status(struct seq_file *seq, struct mddev *mddev)
> * - recovery is interrupted.
> * - &mddev->degraded is bumped.
> *
> - * @rdev is marked as &Faulty excluding case when array is failed and
> - * &mddev->fail_last_dev is off.
> + * If @rdev has &FailfastIOFailure and it is the 'last' rdev,
> + * then @mddev and @rdev will not be marked as failed.
> + *
> + * @rdev is marked as &Faulty excluding any cases:
> + * - when @mddev is failed and &mddev->fail_last_dev is off
> + * - when @rdev is last device and &FailfastIOFailure flag is set
> */
> static void raid1_error(struct mddev *mddev, struct md_rdev *rdev)
> {
> @@ -1758,6 +1763,13 @@ static void raid1_error(struct mddev *mddev, struct md_rdev *rdev)
>
> if (test_bit(In_sync, &rdev->flags) &&
> (conf->raid_disks - mddev->degraded) == 1) {
> + if (test_and_clear_bit(FailfastIOFailure, &rdev->flags)) {
> + spin_unlock_irqrestore(&conf->device_lock, flags);
> + pr_warn_ratelimited("md/raid1:%s: Failfast IO failure on %pg, "
> + "last device but ignoring it\n",
> + mdname(mddev), rdev->bdev);
> + return;
> + }
> set_bit(MD_BROKEN, &mddev->flags);
>
> if (!mddev->fail_last_dev) {
> @@ -2148,6 +2160,7 @@ static int fix_sync_read_error(struct r1bio *r1_bio)
> if (test_bit(FailFast, &rdev->flags)) {
> /* Don't try recovering from here - just fail it
> * ... unless it is the last working device of course */
> + set_bit(FailfastIOFailure, &rdev->flags);
> md_error(mddev, rdev);
> if (test_bit(Faulty, &rdev->flags))
> /* Don't try to read from here, but make sure
> @@ -2652,6 +2665,7 @@ static void handle_read_error(struct r1conf *conf, struct r1bio *r1_bio)
> fix_read_error(conf, r1_bio);
> unfreeze_array(conf);
> } else if (mddev->ro == 0 && test_bit(FailFast, &rdev->flags)) {
> + set_bit(FailfastIOFailure, &rdev->flags);
> md_error(mddev, rdev);
> } else {
> r1_bio->bios[r1_bio->read_disk] = IO_BLOCKED;
> diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> index b60c30bfb6c7..530ad6503189 100644
> --- a/drivers/md/raid10.c
> +++ b/drivers/md/raid10.c
> @@ -488,6 +488,7 @@ static void raid10_end_write_request(struct bio *bio)
> dec_rdev = 0;
> if (test_bit(FailFast, &rdev->flags) &&
> (bio->bi_opf & MD_FAILFAST)) {
> + set_bit(FailfastIOFailure, &rdev->flags);
> md_error(rdev->mddev, rdev);
> }
>
> @@ -1995,8 +1996,12 @@ static int enough(struct r10conf *conf, int ignore)
> * - recovery is interrupted.
> * - &mddev->degraded is bumped.
> *
> - * @rdev is marked as &Faulty excluding case when array is failed and
> - * &mddev->fail_last_dev is off.
> + * If @rdev has &FailfastIOFailure and it is the 'last' rdev,
> + * then @mddev and @rdev will not be marked as failed.
> + *
> + * @rdev is marked as &Faulty excluding any cases:
> + * - when @mddev is failed and &mddev->fail_last_dev is off
> + * - when @rdev is last device and &FailfastIOFailure flag is set
> */
> static void raid10_error(struct mddev *mddev, struct md_rdev *rdev)
> {
> @@ -2006,6 +2011,13 @@ static void raid10_error(struct mddev *mddev, struct md_rdev *rdev)
> spin_lock_irqsave(&conf->device_lock, flags);
>
> if (test_bit(In_sync, &rdev->flags) && !enough(conf, rdev->raid_disk)) {
> + if (test_and_clear_bit(FailfastIOFailure, &rdev->flags)) {
> + spin_unlock_irqrestore(&conf->device_lock, flags);
> + pr_warn_ratelimited("md/raid10:%s: Failfast IO failure on %pg, "
> + "last device but ignoring it\n",
> + mdname(mddev), rdev->bdev);
> + return;
> + }
> set_bit(MD_BROKEN, &mddev->flags);
>
> if (!mddev->fail_last_dev) {
> @@ -2413,6 +2425,7 @@ static void sync_request_write(struct mddev *mddev, struct r10bio *r10_bio)
> continue;
> } else if (test_bit(FailFast, &rdev->flags)) {
> /* Just give up on this device */
> + set_bit(FailfastIOFailure, &rdev->flags);
> md_error(rdev->mddev, rdev);
> continue;
> }
> @@ -2865,8 +2878,10 @@ static void handle_read_error(struct mddev *mddev, struct r10bio *r10_bio)
> freeze_array(conf, 1);
> fix_read_error(conf, mddev, r10_bio);
> unfreeze_array(conf);
> - } else
> + } else {
> + set_bit(FailfastIOFailure, &rdev->flags);
> md_error(mddev, rdev);
> + }
>
> rdev_dec_pending(rdev, mddev);
> r10_bio->state = 0;
> --
> 2.50.1
>
>
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