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    Subject[PATCH AUTOSEL 5.17 33/60] md: don't unregister sync_thread with reconfig_mutex held
    Date
    From: Guoqing Jiang <guoqing.jiang@cloud.ionos.com>

    [ Upstream commit 8b48ec23cc51a4e7c8dbaef5f34ebe67e1a80934 ]

    Unregister sync_thread doesn't need to hold reconfig_mutex since it
    doesn't reconfigure array.

    And it could cause deadlock problem for raid5 as follows:

    1. process A tried to reap sync thread with reconfig_mutex held after echo
    idle to sync_action.
    2. raid5 sync thread was blocked if there were too many active stripes.
    3. SB_CHANGE_PENDING was set (because of write IO comes from upper layer)
    which causes the number of active stripes can't be decreased.
    4. SB_CHANGE_PENDING can't be cleared since md_check_recovery was not able
    to hold reconfig_mutex.

    More details in the link:
    https://lore.kernel.org/linux-raid/5ed54ffc-ce82-bf66-4eff-390cb23bc1ac@molgen.mpg.de/T/#t

    And add one parameter to md_reap_sync_thread since it could be called by
    dm-raid which doesn't hold reconfig_mutex.

    Reported-and-tested-by: Donald Buczek <buczek@molgen.mpg.de>
    Signed-off-by: Guoqing Jiang <guoqing.jiang@cloud.ionos.com>
    Signed-off-by: Song Liu <song@kernel.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/md/dm-raid.c | 2 +-
    drivers/md/md.c | 14 +++++++++-----
    drivers/md/md.h | 2 +-
    3 files changed, 11 insertions(+), 7 deletions(-)

    diff --git a/drivers/md/dm-raid.c b/drivers/md/dm-raid.c
    index 2b26435a6946..a5cc73d8f535 100644
    --- a/drivers/md/dm-raid.c
    +++ b/drivers/md/dm-raid.c
    @@ -3730,7 +3730,7 @@ static int raid_message(struct dm_target *ti, unsigned int argc, char **argv,
    if (!strcasecmp(argv[0], "idle") || !strcasecmp(argv[0], "frozen")) {
    if (mddev->sync_thread) {
    set_bit(MD_RECOVERY_INTR, &mddev->recovery);
    - md_reap_sync_thread(mddev);
    + md_reap_sync_thread(mddev, false);
    }
    } else if (decipher_sync_action(mddev, mddev->recovery) != st_idle)
    return -EBUSY;
    diff --git a/drivers/md/md.c b/drivers/md/md.c
    index 4d38bd7dadd6..8efe9c8ff937 100644
    --- a/drivers/md/md.c
    +++ b/drivers/md/md.c
    @@ -4844,7 +4844,7 @@ action_store(struct mddev *mddev, const char *page, size_t len)
    flush_workqueue(md_misc_wq);
    if (mddev->sync_thread) {
    set_bit(MD_RECOVERY_INTR, &mddev->recovery);
    - md_reap_sync_thread(mddev);
    + md_reap_sync_thread(mddev, true);
    }
    mddev_unlock(mddev);
    }
    @@ -6214,7 +6214,7 @@ static void __md_stop_writes(struct mddev *mddev)
    flush_workqueue(md_misc_wq);
    if (mddev->sync_thread) {
    set_bit(MD_RECOVERY_INTR, &mddev->recovery);
    - md_reap_sync_thread(mddev);
    + md_reap_sync_thread(mddev, true);
    }

    del_timer_sync(&mddev->safemode_timer);
    @@ -9321,7 +9321,7 @@ void md_check_recovery(struct mddev *mddev)
    * ->spare_active and clear saved_raid_disk
    */
    set_bit(MD_RECOVERY_INTR, &mddev->recovery);
    - md_reap_sync_thread(mddev);
    + md_reap_sync_thread(mddev, true);
    clear_bit(MD_RECOVERY_RECOVER, &mddev->recovery);
    clear_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
    clear_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags);
    @@ -9356,7 +9356,7 @@ void md_check_recovery(struct mddev *mddev)
    goto unlock;
    }
    if (mddev->sync_thread) {
    - md_reap_sync_thread(mddev);
    + md_reap_sync_thread(mddev, true);
    goto unlock;
    }
    /* Set RUNNING before clearing NEEDED to avoid
    @@ -9429,14 +9429,18 @@ void md_check_recovery(struct mddev *mddev)
    }
    EXPORT_SYMBOL(md_check_recovery);

    -void md_reap_sync_thread(struct mddev *mddev)
    +void md_reap_sync_thread(struct mddev *mddev, bool reconfig_mutex_held)
    {
    struct md_rdev *rdev;
    sector_t old_dev_sectors = mddev->dev_sectors;
    bool is_reshaped = false;

    + if (reconfig_mutex_held)
    + mddev_unlock(mddev);
    /* resync has finished, collect result */
    md_unregister_thread(&mddev->sync_thread);
    + if (reconfig_mutex_held)
    + mddev_lock_nointr(mddev);
    if (!test_bit(MD_RECOVERY_INTR, &mddev->recovery) &&
    !test_bit(MD_RECOVERY_REQUESTED, &mddev->recovery) &&
    mddev->degraded != mddev->raid_disks) {
    diff --git a/drivers/md/md.h b/drivers/md/md.h
    index f1bf3625ef4c..577f0c5ef2ed 100644
    --- a/drivers/md/md.h
    +++ b/drivers/md/md.h
    @@ -711,7 +711,7 @@ extern struct md_thread *md_register_thread(
    extern void md_unregister_thread(struct md_thread **threadp);
    extern void md_wakeup_thread(struct md_thread *thread);
    extern void md_check_recovery(struct mddev *mddev);
    -extern void md_reap_sync_thread(struct mddev *mddev);
    +extern void md_reap_sync_thread(struct mddev *mddev, bool reconfig_mutex_held);
    extern int mddev_init_writes_pending(struct mddev *mddev);
    extern bool md_write_start(struct mddev *mddev, struct bio *bi);
    extern void md_write_inc(struct mddev *mddev, struct bio *bi);
    --
    2.35.1
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