Re: Linux RAID with btrfs stuck and consume 100 % CPU

[Guoqing Jiang <guoqing.jiang@xxxxxxxxxxxxxxx>]

Hi,

On 7/22/20 10:47 PM, Vojtech Myslivec wrote:
> 1. What should be the cause of this problem?

Just a quick glance based on the stacks which you attached, I guess it 
could be
a deadlock issue of raid5 cache super write.

Maybe the commit 8e018c21da3f ("raid5-cache: fix a deadlock in superblock
write") didn't fix the problem completely.  Cc Song.

And I am curious why md thread is not waked if mddev_trylock fails, you can
give it a try but I can't promise it helps ...

--- a/drivers/md/raid5-cache.c
+++ b/drivers/md/raid5-cache.c
@@ -1337,8 +1337,10 @@ static void 
r5l_write_super_and_discard_space(struct r5l_log *log,
         */
        set_mask_bits(&mddev->sb_flags, 0,
                BIT(MD_SB_CHANGE_DEVS) | BIT(MD_SB_CHANGE_PENDING));
-       if (!mddev_trylock(mddev))
+       if (!mddev_trylock(mddev)) {
+               md_wakeup_thread(mddev->thread);
                return;
+       }
        md_update_sb(mddev, 1);
        mddev_unlock(mddev);


Thanks,
Guoqing