Patch "md: always set THREAD_WAKEUP and wake up wqueue if thread existed" has been added to the 4.14-stable tree

This is a note to let you know that I've just added the patch titled

md: always set THREAD_WAKEUP and wake up wqueue if thread existed

to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
md-always-set-thread_wakeup-and-wake-up-wqueue-if-thread-existed.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Guoqing Jiang <[email protected]>
Date: Mon, 9 Oct 2017 10:32:48 +0800
Subject: md: always set THREAD_WAKEUP and wake up wqueue if thread existed

From: Guoqing Jiang <[email protected]>

[ Upstream commit d1d90147c9680aaec4a5757932c2103c42c9c23b ]

Since commit 4ad23a976413 ("MD: use per-cpu counter for writes_pending"), the wait_queue is only got invoked if THREAD_WAKEUP is not set previously.

With above change, I can see process_metadata_update could always hang on the wait queue, because mddev->thread could stay on 'D' status and the THREAD_WAKEUP flag is not cleared since there are lots of place to wake up mddev->thread. Then deadlock happened as follows:

linux175:~ # ps aux|grep md|grep D

root    20117   0.0 0.0         0   0 ? D   03:45   0:00 [md0_raid1]
root    20125   0.0 0.0         0   0 ? D   03:45   0:00 [md0_cluster_rec]
linux175:~ # cat /proc/20117/stack
[<ffffffffa0635604>] dlm_lock_sync+0x94/0xd0 [md_cluster]
[<ffffffffa0635674>] lock_token+0x34/0xd0 [md_cluster]
[<ffffffffa0635804>] metadata_update_start+0x64/0x110 [md_cluster]
[<ffffffffa04d985b>] md_update_sb.part.58+0x9b/0x860 [md_mod]
[<ffffffffa04da035>] md_update_sb+0x15/0x30 [md_mod]
[<ffffffffa04dc066>] md_check_recovery+0x266/0x490 [md_mod]
[<ffffffffa06450e2>] raid1d+0x42/0x810 [raid1]
[<ffffffffa04d2252>] md_thread+0x122/0x150 [md_mod]
[<ffffffff81091741>] kthread+0x101/0x140
linux175:~ # cat /proc/20125/stack
[<ffffffffa0636679>] recv_daemon+0x3f9/0x5c0 [md_cluster]
[<ffffffffa04d2252>] md_thread+0x122/0x150 [md_mod]
[<ffffffff81091741>] kthread+0x101/0x140

So let's revert the part of code in the commit to resovle the problem since we can't get lots of benefits of previous change.

---
 drivers/md/md.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

@@ -7468,8 +7468,8 @@ void md_wakeup_thread(struct md_thread *
 {
 	if (thread) {
 		pr_debug("md: waking up MD thread %s.\n", thread->tsk->comm);
-		if (!test_and_set_bit(THREAD_WAKEUP, &thread->flags))
-			wake_up(&thread->wqueue);
+		set_bit(THREAD_WAKEUP, &thread->flags);
+		wake_up(&thread->wqueue);
 	}
 }
 EXPORT_SYMBOL(md_wakeup_thread);

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/md-always-set-thread_wakeup-and-wake-up-wqueue-if-thread-existed.patch