Patch "raid1: include bio_end_io_list in nr_queued to prevent freeze_array hang" has been added to the 4.5-stable tree

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

raid1: include bio_end_io_list in nr_queued to prevent freeze_array hang

to the 4.5-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:
raid1-include-bio_end_io_list-in-nr_queued-to-prevent-freeze_array-hang.patch
and it can be found in the queue-4.5 subdirectory.

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

From: Nate Dailey <[email protected]>
Date: Mon, 29 Feb 2016 10:43:58 -0500
Subject: raid1: include bio_end_io_list in nr_queued to prevent freeze_array hang

From: Nate Dailey <[email protected]>

commit ccfc7bf1f09d6190ef86693ddc761d5fe3fa47cb upstream.

If raid1d is handling a mix of read and write errors, handle_read_error's call to freeze_array can get stuck.

This can happen because, though the bio_end_io_list is initially drained, writes can be added to it via handle_write_finished as the retry_list is processed. These writes contribute to nr_pending but are not included in nr_queued.

If a later entry on the retry_list triggers a call to handle_read_error, freeze array hangs waiting for nr_pending == nr_queued+extra. The writes on the bio_end_io_list aren't included in nr_queued so the condition will never be satisfied.

To prevent the hang, include bio_end_io_list writes in nr_queued.

There's probably a better way to handle decrementing nr_queued, but this seemed like the safest way to avoid breaking surrounding code.

I'm happy to supply the script I used to repro this hang.

---
 drivers/md/raid1.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

@@ -2274,6 +2274,7 @@ static void handle_write_finished(struct
 	if (fail) {
 		spin_lock_irq(&conf->device_lock);
 		list_add(&r1_bio->retry_list, &conf->bio_end_io_list);
+		conf->nr_queued++;
 		spin_unlock_irq(&conf->device_lock);
 		md_wakeup_thread(conf->mddev->thread);
 	} else {

@@ -2391,8 +2392,10 @@ static void raid1d(struct md_thread *thr
 		LIST_HEAD(tmp);
 		spin_lock_irqsave(&conf->device_lock, flags);
 		if (!test_bit(MD_CHANGE_PENDING, &mddev->flags)) {
-			list_add(&tmp, &conf->bio_end_io_list);
-			list_del_init(&conf->bio_end_io_list);
+			while (!list_empty(&conf->bio_end_io_list)) {
+				list_move(conf->bio_end_io_list.prev, &tmp);
+				conf->nr_queued--;
+			}
 		}
 		spin_unlock_irqrestore(&conf->device_lock, flags);
 		while (!list_empty(&tmp)) {

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

queue-4.5/raid10-include-bio_end_io_list-in-nr_queued-to-prevent-freeze_array-hang.patch queue-4.5/raid1-include-bio_end_io_list-in-nr_queued-to-prevent-freeze_array-hang.patch