Dear Guoqing,
On 13.02.21 01:49, Guoqing Jiang wrote:
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@xxxxxxxxxxxxx/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@xxxxxxxxxxxxx>
Signed-off-by: Guoqing Jiang <guoqing.jiang@xxxxxxxxxxxxxxx>
---
V2:
1. add one parameter to md_reap_sync_thread per Jack's suggestion.
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 cab12b2..0c4cbba 100644
--- a/drivers/md/dm-raid.c
+++ b/drivers/md/dm-raid.c
@@ -3668,7 +3668,7 @@ 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 ca40942..0c12b7f 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -4857,7 +4857,7 @@ 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);
}
@@ -6234,7 +6234,7 @@ 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);
@@ -9256,7 +9256,7 @@ 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);
@@ -9291,7 +9291,7 @@ 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
@@ -9364,14 +9364,18 @@ 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;
/* resync has finished, collect result */
+ if (reconfig_mutex_held)
+ mddev_unlock(mddev);
If one thread got here, e.g. via action_store( /* "idle" */ ), now that the mutex is unlocked, is there anything which would prevent another thread getting here as well, e.g. via the same path?
If not, they both might call
md_unregister_thread(&mddev->sync_thread);
Which is not reentrant:
void md_unregister_thread(struct md_thread **threadp)
{
struct md_thread *thread = *threadp;
if (!thread)
return;
pr_debug("interrupting MD-thread pid %d\n", task_pid_nr(thread->tsk));
/* Locking ensures that mddev_unlock does not wake_up a
* non-existent thread
*/
spin_lock(&pers_lock);
*threadp = NULL;
spin_unlock(&pers_lock);
kthread_stop(thread->tsk);
kfree(thread);
}
This might be a preexisting problem, because the call site in dm-raid.c, which you updated to `md_reap_sync_thread(mddev, false);`, didn't hold the mutex anyway.
Am I missing something? Probably, I do.
Otherwise: Move the deref of threadp in md_unregister_thread() into the spinlock scope?
Best
Donald
+ 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 34070ab..7ae3d98 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -705,7 +705,7 @@ 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);
--
Donald Buczek
buczek@xxxxxxxxxxxxx
Tel: +49 30 8413 1433
