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Date:   Thu, 20 Apr 2023 23:27:44 +0100
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     NeilBrown <neilb@suse.de>
Cc:     Christian Brauner <brauner@kernel.org>,
        Jeff Layton <jlayton@kernel.org>,
        Dave Wysochanski <dwysocha@redhat.com>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        linux-nfs <linux-nfs@vger.kernel.org>,
        David Howells <dhowells@redhat.com>,
        Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH/RFC] VFS: LOOKUP_MOUNTPOINT should used cached info
 whenever possible.
Message-ID: <20230420222744.GU3390869@ZenIV>
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On Fri, Apr 21, 2023 at 08:01:09AM +1000, NeilBrown wrote:
> On Fri, 21 Apr 2023, Al Viro wrote:
> > On Tue, Apr 18, 2023 at 07:26:34AM +1000, NeilBrown wrote:
> > 
> > > MNT_FORCE is, I think, a good idea and a needed functionality that has
> > > never been implemented well.
> > > MNT_FORCE causes nfs_umount_begin to be called as you noted, which
> > > aborts all pending RPCs on that filesystem.
> > 
> > Suppose it happens to be mounted in another namespace as well.  Or bound
> > at different mountpoint, for that matter.  What should MNT_FORCE do?
> > 
> 
> 1/ set a "forced-unmount" flag on the vfs_mount which causes any syscall
>    that uses the vfsmount (whether from an fd, or found in a path walk,
>    or elsewhere), except for close(), to abort with an error;
> 2/ call ->umount_begin passing in the vfs_mount.  The fs can abort any
>    outstanding transaction on any fd from that vfs_mount.

How the hell would you recognize those?