linux-kernel - Re: [PATCH Next] copy_mnt_ns(): Remove unnecessary unlock

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Message-ID: <20250924175641.GT39973@ZenIV>
Date: Wed, 24 Sep 2025 18:56:41 +0100
From: Al Viro <viro@...iv.linux.org.uk>
To: Jan Kara <jack@...e.cz>
Cc: Edward Adam Davis <eadavis@...com>,
	syzbot+0d671007a95cd2835e05@...kaller.appspotmail.com,
	brauner@...nel.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH Next] copy_mnt_ns(): Remove unnecessary unlock

On Wed, Sep 24, 2025 at 02:03:56PM +0200, Jan Kara wrote:
> On Wed 24-09-25 18:29:04, Edward Adam Davis wrote:
> > This code segment is already protected by guards, namespace_unlock()
> > should not appear here.
> > 
> > Reported-by: syzbot+0d671007a95cd2835e05@...kaller.appspotmail.com
> > Closes: https://syzkaller.appspot.com/bug?extid=0d671007a95cd2835e05
> > Signed-off-by: Edward Adam Davis <eadavis@...com>
> 
> Indeed. Feel free to add:
> 
> Reviewed-by: Jan Kara <jack@...e.cz>

I wonder where does that line come from, though.  Mismerge somewhere?
d7b7253a0adc "copy_mnt_ns(): use guards" includes this:

@@ -4185,13 +4186,11 @@ struct mnt_namespace *copy_mnt_ns(unsigned long flags, struct mnt_namespace *ns,
 	new = copy_tree(old, old->mnt.mnt_root, copy_flags);
 	if (IS_ERR(new)) {
 		emptied_ns = new_ns;
-		namespace_unlock();
 		return ERR_CAST(new);
 	}
 	if (user_ns != ns->user_ns) {
-		lock_mount_hash();
+		guard(mount_writer)();
 		lock_mnt_tree(new);
-		unlock_mount_hash();
 	}
 	new_ns->root = new;