Re: [PATCH] fs/namei: fix WARNING in do_mknodat due to invalid inode unlock

[Al Viro]

On Sun, Aug 24, 2025 at 08:07:14PM +0100, Al Viro wrote:
> On Mon, Aug 25, 2025 at 12:23:03AM +0530, ssranevjti@xxxxxxxxx wrote:
> > From: Shaurya Rane <ssrane_b23@xxxxxxxxxxxxx>
> > 
> > The done_path_create() function unconditionally calls inode_unlock() on
> > path->dentry->d_inode without verifying that the path and inode are valid.
> > Under certain error conditions or race scenarios, this can lead to attempting
> > to unlock an inode that was never locked or has been corrupted, resulting in
> > a WARNING from the rwsem debugging code.
> > 
> > Add defensive checks to ensure both path->dentry and path->dentry->d_inode
> > are valid before attempting to unlock. This prevents the rwsem warning while
> > maintaining existing behavior for normal cases.
> > 
> > Reported-by: syzbot+0cee785b798102696a4b@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> No.  You are papering over some bugs you have not even bothered to describe -
> "certain error conditions or race scenarios" is as useless as it gets.
> 
> Don't do that.  Fixing a bug found by syzbot is useful; papering over
> it does no good whatsoever.
> 
> NAK.

Incidentally, syzbot report in question seems to be the one at

https://lore.kernel.org/all/689edffb.050a0220.e29e5.000d.GAE@xxxxxxxxxx/
"[syzbot] [gfs2?] WARNING in do_mknodat (3)"

I won't have time to look at it in details until tomorrow, though.

Again, the patch upthread is no-go.  Whatever is going on with that
reporducer, this is not a fix.