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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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