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	Mon, 21 Apr 2025 17:03:19 +0000
Date: Mon, 21 Apr 2025 18:03:19 +0100
From: Al Viro <viro@zeniv.linux.org.uk>
To: Christian Brauner <brauner@kernel.org>
Cc: linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH][RFC] ->mnt_devname is never NULL
Message-ID: <20250421170319.GX2023217@ZenIV>
References: <20250421033509.GV2023217@ZenIV>
 <20250421-annehmbar-fotoband-eb32f31f6124@brauner>
 <20250421162947.GW2023217@ZenIV>
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Sender: Al Viro <viro@ftp.linux.org.uk>

On Mon, Apr 21, 2025 at 05:29:47PM +0100, Al Viro wrote:

> What's to prevent the 'beneath' case from getting mnt mount --move'd
> away *AND* the ex-parent from getting unmounted while we are blocked
> in inode_lock?  At this point we are not holding any locks whatsoever
> (and all mount-related locks nest inside inode_lock(), so we couldn't
> hold them there anyway).
> 
> Hit that race and watch a very unhappy umount...

While we are at it, in normal case inode_unlock() in unlock_mount()
is safe since we have dentry (and associated mount) pinned by
struct path we'd fed to matching lock_mount().  No longer true for
the 'beneath' case, AFAICS...