Hi,
在 2023/12/02 6:08, Song Liu 写道:
On Tue, Nov 28, 2023 at 8:32 PM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:
From: Yu Kuai <yukuai3@xxxxxxxxxx>
Currently sync thread is stopped from multiple contex:
- idle_sync_thread
- frozen_sync_thread
- __md_stop_writes
- md_set_readonly
- do_md_stop
And there are some problems:
1) sync_work is flushed while reconfig_mutex is grabbed, this can
deadlock because the work function will grab reconfig_mutex as well.
2) md_reap_sync_thread() can't be called directly while md_do_sync() is
not finished yet, for example, commit 130443d60b1b ("md: refactor
idle/frozen_sync_thread() to fix deadlock").
3) If MD_RECOVERY_RUNNING is not set, there is no need to stop
sync_thread at all because sync_thread must not be registered.
Factor out a helper prepare_to_stop_sync_thread(), so that above contex
will behave the same. Fix 1) by flushing sync_work after reconfig_mutex
is released, before waiting for sync_thread to be done; Fix 2) bt
letting daemon thread to unregister sync_thread; Fix 3) by always
checking MD_RECOVERY_RUNNING first.
Fixes: db5e653d7c9f ("md: delay choosing sync action to md_start_sync()")
Acked-by: Xiao Ni <xni@xxxxxxxxxx>
Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
drivers/md/md.c | 96 +++++++++++++++++++++++--------------------------
1 file changed, 45 insertions(+), 51 deletions(-)
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 2d8e45a1af23..05902e36db66 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -4840,26 +4840,9 @@ action_show(struct mddev *mddev, char *page)
return sprintf(page, "%s\n", type);
}
-static void stop_sync_thread(struct mddev *mddev)
+static void prepare_to_stop_sync_thread(struct mddev *mddev)
+ __releases(&mddev->reconfig_mutex)
{
- if (!test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
- return;
-
- if (mddev_lock(mddev))
- return;
-
- /*
- * Check again in case MD_RECOVERY_RUNNING is cleared before lock is
- * held.
- */
- if (!test_bit(MD_RECOVERY_RUNNING, &mddev->recovery)) {
- mddev_unlock(mddev);
- return;
- }
-
- if (work_pending(&mddev->sync_work))
- flush_workqueue(md_misc_wq);
-
set_bit(MD_RECOVERY_INTR, &mddev->recovery);
/*
* Thread might be blocked waiting for metadata update which will now
@@ -4868,6 +4851,8 @@ static void stop_sync_thread(struct mddev *mddev)
md_wakeup_thread_directly(mddev->sync_thread);
mddev_unlock(mddev);
+ if (work_pending(&mddev->sync_work))
+ flush_work(&mddev->sync_work);
}
static void idle_sync_thread(struct mddev *mddev)
@@ -4876,10 +4861,20 @@ static void idle_sync_thread(struct mddev *mddev)
mutex_lock(&mddev->sync_mutex);
clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
- stop_sync_thread(mddev);
- wait_event(resync_wait, sync_seq != atomic_read(&mddev->sync_seq) ||
+ if (mddev_lock(mddev)) {
+ mutex_unlock(&mddev->sync_mutex);
+ return;
+ }
+
+ if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery)) {
+ prepare_to_stop_sync_thread(mddev);
+ wait_event(resync_wait,
+ sync_seq != atomic_read(&mddev->sync_seq) ||
!test_bit(MD_RECOVERY_RUNNING, &mddev->recovery));
+ } else {
+ mddev_unlock(mddev);
+ }
We have a few patterns like this:
if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery)) {
prepare_to_stop_sync_thread(mddev);
wait_event(resync_wait,
sync_seq != atomic_read(&mddev->sync_seq) ||
!test_bit(MD_RECOVERY_RUNNING, &mddev->recovery));
} else {
mddev_unlock(mddev);
}
This is pretty confusing. Maybe try something like (untested)
static void stop_sync_thread(struct mddev *mddev,
bool do_unlock, bool check_sync_seq)
Yes, if we can accept use parameter to distinguish different use case.
Thanks,
Kuai
{
if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery)) {
if (do_unlock)
mddev_unlock(mddev);
return;
}
set_bit(MD_RECOVERY_INTR, &mddev->recovery);
/*
* Thread might be blocked waiting for metadata update which will now
* never happen
*/
md_wakeup_thread_directly(mddev->sync_thread);
mddev_unlock(mddev);
if (work_pending(&mddev->sync_work))
flush_work(&mddev->sync_work);
wait_event(resync_wait,
!test_bit(MD_RECOVERY_RUNNING, &mddev->recovery) ||
(check_sync_seq && sync_seq !=
atomic_read(&mddev->sync_seq)));
if (!do_unlock)
mddev_lock_nointr(mddev);
}
Thanks,
Song
.
