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    Subject[PATCH 4.14 34/61] md: always hold reconfig_mutex when calling mddev_suspend()
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: NeilBrown <neilb@suse.com>

    commit 4d5324f760aacaefeb721b172aa14bf66045c332 upstream.

    Most often mddev_suspend() is called with
    reconfig_mutex held. Make this a requirement in
    preparation a subsequent patch. Also require
    reconfig_mutex to be held for mddev_resume(),
    partly for symmetry and partly to guarantee
    no races with incr/decr of mddev->suspend.

    Taking the mutex in r5c_disable_writeback_async() is
    a little tricky as this is called from a work queue
    via log->disable_writeback_work, and flush_work()
    is called on that while holding ->reconfig_mutex.
    If the work item hasn't run before flush_work()
    is called, the work function will not be able to
    get the mutex.

    So we use mddev_trylock() inside the wait_event() call, and have that
    abort when conf->log is set to NULL, which happens before
    flush_work() is called.
    We wait in mddev->sb_wait and ensure this is woken
    when any of the conditions change. This requires
    waking mddev->sb_wait in mddev_unlock(). This is only
    like to trigger extra wake_ups of threads that needn't
    be woken when metadata is being written, and that
    doesn't happen often enough that the cost would be
    noticeable.

    Signed-off-by: NeilBrown <neilb@suse.com>
    Signed-off-by: Shaohua Li <shli@fb.com>
    Signed-off-by: Jack Wang <jinpu.wang@profitbricks.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/md/dm-raid.c | 10 ++++++++--
    drivers/md/md.c | 3 +++
    drivers/md/raid5-cache.c | 18 +++++++++++++-----
    3 files changed, 24 insertions(+), 7 deletions(-)

    --- a/drivers/md/dm-raid.c
    +++ b/drivers/md/dm-raid.c
    @@ -3637,8 +3637,11 @@ static void raid_postsuspend(struct dm_t
    {
    struct raid_set *rs = ti->private;

    - if (!test_and_set_bit(RT_FLAG_RS_SUSPENDED, &rs->runtime_flags))
    + if (!test_and_set_bit(RT_FLAG_RS_SUSPENDED, &rs->runtime_flags)) {
    + mddev_lock_nointr(&rs->md);
    mddev_suspend(&rs->md);
    + mddev_unlock(&rs->md);
    + }

    rs->md.ro = 1;
    }
    @@ -3898,8 +3901,11 @@ static void raid_resume(struct dm_target
    if (!(rs->ctr_flags & RESUME_STAY_FROZEN_FLAGS))
    clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);

    - if (test_and_clear_bit(RT_FLAG_RS_SUSPENDED, &rs->runtime_flags))
    + if (test_and_clear_bit(RT_FLAG_RS_SUSPENDED, &rs->runtime_flags)) {
    + mddev_lock_nointr(mddev);
    mddev_resume(mddev);
    + mddev_unlock(mddev);
    + }
    }

    static struct target_type raid_target = {
    --- a/drivers/md/md.c
    +++ b/drivers/md/md.c
    @@ -344,6 +344,7 @@ static blk_qc_t md_make_request(struct r
    void mddev_suspend(struct mddev *mddev)
    {
    WARN_ON_ONCE(mddev->thread && current == mddev->thread->tsk);
    + lockdep_assert_held(&mddev->reconfig_mutex);
    if (mddev->suspended++)
    return;
    synchronize_rcu();
    @@ -357,6 +358,7 @@ EXPORT_SYMBOL_GPL(mddev_suspend);

    void mddev_resume(struct mddev *mddev)
    {
    + lockdep_assert_held(&mddev->reconfig_mutex);
    if (--mddev->suspended)
    return;
    wake_up(&mddev->sb_wait);
    @@ -663,6 +665,7 @@ void mddev_unlock(struct mddev *mddev)
    */
    spin_lock(&pers_lock);
    md_wakeup_thread(mddev->thread);
    + wake_up(&mddev->sb_wait);
    spin_unlock(&pers_lock);
    }
    EXPORT_SYMBOL_GPL(mddev_unlock);
    --- a/drivers/md/raid5-cache.c
    +++ b/drivers/md/raid5-cache.c
    @@ -693,6 +693,8 @@ static void r5c_disable_writeback_async(
    struct r5l_log *log = container_of(work, struct r5l_log,
    disable_writeback_work);
    struct mddev *mddev = log->rdev->mddev;
    + struct r5conf *conf = mddev->private;
    + int locked = 0;

    if (log->r5c_journal_mode == R5C_JOURNAL_MODE_WRITE_THROUGH)
    return;
    @@ -701,11 +703,15 @@ static void r5c_disable_writeback_async(

    /* wait superblock change before suspend */
    wait_event(mddev->sb_wait,
    - !test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags));
    -
    - mddev_suspend(mddev);
    - log->r5c_journal_mode = R5C_JOURNAL_MODE_WRITE_THROUGH;
    - mddev_resume(mddev);
    + conf->log == NULL ||
    + (!test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags) &&
    + (locked = mddev_trylock(mddev))));
    + if (locked) {
    + mddev_suspend(mddev);
    + log->r5c_journal_mode = R5C_JOURNAL_MODE_WRITE_THROUGH;
    + mddev_resume(mddev);
    + mddev_unlock(mddev);
    + }
    }

    static void r5l_submit_current_io(struct r5l_log *log)
    @@ -3161,6 +3167,8 @@ void r5l_exit_log(struct r5conf *conf)
    conf->log = NULL;
    synchronize_rcu();

    + /* Ensure disable_writeback_work wakes up and exits */
    + wake_up(&conf->mddev->sb_wait);
    flush_work(&log->disable_writeback_work);
    md_unregister_thread(&log->reclaim_thread);
    mempool_destroy(log->meta_pool);

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