Re: [PATCH v10 5/5] ext4: prevent deadlock from duplicate EA inode references on corrupted fs

[Zhou, Yun]

On 6/27/26 01:23, Jan Kara wrote:
> On Thu 25-06-26 23:29:41, Yun Zhou wrote:
> > On a corrupted filesystem, multiple xattr entries may reference the same
> > EA inode.  When ext4_xattr_inode_dec_ref_all() processes such entries, it
> > can dec_ref the EA inode (setting nlink=0) and queue it for deferred iput.
> > If the deferred worker runs before the loop processes the duplicate entry,
> > the second iget() may block on I_FREEING while the worker's eviction waits
> > for the caller's transaction to commit -- classic ABBA deadlock.
>
> Hum, this looks possible but it isn't a new thing this patch set
> introduces. Even before if you had corrupted filesystem,
> ext4_xattr_inode_array_free() from ext4_evict_inode() could deadlock in a
> similar way against say ext4_xattr_inode_dec_ref_all() (but practially
> anything calling ext4_xattr_inode_iget() while holding a transaction
> handle). So please leave this alone for now. We can look into that once
> other EA inode settle.

Mainly because sashiko-bot always flags this issue every time. I've further
improved the patch and believe I've thoroughly plugged this loophole. I will
include it in v11, and please take a look when you have a chance. If it 
still
has issues, or if you think it's redundant or inelegant, we can just 
drop it.

BR,
Yun