linux-kernel - Re: Upcoming: Notifications, FS notifications and fsinfo()

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Message-ID: <3072199.1585842165@warthog.procyon.org.uk>
Date:   Thu, 02 Apr 2020 16:42:45 +0100
From:   David Howells <dhowells@...hat.com>
To:     Miklos Szeredi <miklos@...redi.hu>
Cc:     dhowells@...hat.com, Karel Zak <kzak@...hat.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>, dray@...hat.com,
        Miklos Szeredi <mszeredi@...hat.com>,
        Steven Whitehouse <swhiteho@...hat.com>,
        Jeff Layton <jlayton@...hat.com>, Ian Kent <raven@...maw.net>,
        andres@...razel.de, keyrings@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Lennart Poettering <lennart@...ttering.net>,
        Aleksa Sarai <cyphar@...har.com>
Subject: Re: Upcoming: Notifications, FS notifications and fsinfo()

Miklos Szeredi <miklos@...redi.hu> wrote:

> > ext4_show_mount(), for example, doesn't lock against "mount -o remount", so
> > the configuration can be changing whilst it's being rendered to text.
> 
> Does s_umount nest inside namespace_sem?  I really don't see the
> relation of those locks.

If I understand aright what Al has told me, it's a bad idea to do any blocking
operation inside of namespace_sem apart from kmalloc(GFP_KERNEL).

David