linux-kernel - Re: [PATCH 13/19] vfs: Add a mount-notification facility [ver #16]

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Date:   Wed, 19 Feb 2020 23:55:26 +0100
From:   Jann Horn <jannh@...gle.com>
To:     David Howells <dhowells@...hat.com>
Cc:     Al Viro <viro@...iv.linux.org.uk>, raven@...maw.net,
        Miklos Szeredi <mszeredi@...hat.com>,
        Christian Brauner <christian@...uner.io>,
        Linux API <linux-api@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        kernel list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 13/19] vfs: Add a mount-notification facility [ver #16]

On Wed, Feb 19, 2020 at 11:40 PM Jann Horn <jannh@...gle.com> wrote:
> On Tue, Feb 18, 2020 at 6:07 PM David Howells <dhowells@...hat.com> wrote:
[...]
> > +                       watch = NULL;
> > +               }
> > +               up_write(&m->mnt.mnt_sb->s_umount);
> > +       } else {
> > +               ret = -EBADSLT;
> > +               if (m->mnt_watchers) {
> > +                       down_write(&m->mnt.mnt_sb->s_umount);
> > +                       ret = remove_watch_from_object(m->mnt_watchers, wqueue,
> > +                                                      (unsigned long)path.dentry,
> > +                                                      false);
>
> What exactly is the implication of only using the dentry as key here
> (and not the mount)? Does this mean that if you watch install watches
> on two bind mounts of the same underlying filesystem, the notification
> mechanism gets confused?

Ah, nevermind, I understand this one now... this operation only
removes watches on this mount with that dentry, and so together, that
means it effectively removes watches by the full path.