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Message-ID: <CALTww2_nJqyA99cG9YNarXEB4wimFK=pKy=qrxdkfB60PaUa1w@mail.gmail.com>
Date: Tue, 16 Dec 2025 20:29:46 +0800
From: Xiao Ni <xni@...hat.com>
To: Kenta Akagi <k@...l.me>
Cc: song@...nel.org, yukuai3@...wei.com, mtkaczyk@...nel.org, 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
On Tue, Dec 16, 2025 at 12:08 AM Kenta Akagi <k@...l.me> wrote:
>
> Hi, Xiao
> Sorry for late reply.
>
> On 2025/11/19 12:13, Xiao Ni wrote:
> > Hi Kenta
> >
> > 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.
>
> I may have been too concerned with maintaining the behavior seen from the user space.
> and I think this method is good.
>
> We may need to consider that raid1/raid10 will never MD_BROKEN when rdev has failfast.
> MD_BROKEN was introduced to raid1/raid10 in 2023, and I believe there are
> almost no cases where people expect it to become "broken" when the last rdev behaves strangely.
> So, rather than complicating error handling for failfast, it seems better to have a way of not
> set MD_BROKEN when failfast is configured.
>
> I'll sending the next patch using this approach.
>
> Thanks!
> Akagi
Hi Akagi
Thanks for your understanding.
Regards
Xiao
>
> >
> > Best Regards
> >
> > Xiao
> >
> > On Fri, Aug 29, 2025 at 12:39 AM Kenta Akagi <k@...l.me <mailto: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 <mailto: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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