Re: [fsdax xfs] Regression panic at inode_switch_wbs_work_fn

[Roman Gushchin <guro@fb.com>]

On Thu, Jul 15, 2021 at 06:10:22PM +0800, Murphy Zhou wrote:
> Hi,
> 
> #Looping generic/270 of xfstests[1] on pmem ramdisk with
> mount option:  -o dax=always
> mkfs.xfs option: -f -b size=4096 -m reflink=0
> can hit this panic now.
> 
> #It's not reproducible on ext4.
> #It's not reproducible without dax=always.

Hi Murphy!

Thank you for the report!

Can you, please, check if the following patch fixes the problem?

Thank you!

--

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 271f2ca862c8..f5561ea7d90a 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -398,12 +398,12 @@ static void cgwb_release_workfn(struct work_struct *work)
        blkcg_unpin_online(blkcg);
 
        fprop_local_destroy_percpu(&wb->memcg_completions);
-       percpu_ref_exit(&wb->refcnt);
 
        spin_lock_irq(&cgwb_lock);
        list_del(&wb->offline_node);
        spin_unlock_irq(&cgwb_lock);
 
+       percpu_ref_exit(&wb->refcnt);
        wb_exit(wb);
        WARN_ON_ONCE(!list_empty(&wb->b_attached));
        kfree_rcu(wb, rcu);