linux-kernel - Re: Inverted mount options completely broken (iversion,relatime)

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Message-ID: <4007797.1596055016@warthog.procyon.org.uk>
Date:   Wed, 29 Jul 2020 21:36:56 +0100
From:   David Howells <dhowells@...hat.com>
To:     Josef Bacik <josef@...icpanda.com>
Cc:     dhowells@...hat.com,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Eric Sandeen <sandeen@...hat.com>,
        Christoph Hellwig <hch@....de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        David Sterba <dsterba@...e.com>
Subject: Re: Inverted mount options completely broken (iversion,relatime)

Josef Bacik <josef@...icpanda.com> wrote:

> So my question is, what do we do here?

Hmmm...  As the code stands, MS_RDONLY, MS_SYNCHRONOUS, MS_MANDLOCK,
MS_I_VERSION and MS_LAZYTIME should all be masked off before the new flags are
set if called from mount(2) rather than fsconfig(2).

do_remount() gives MS_RMT_MASK to fs_context_for_reconfigure() to load into
fc->sb_flags_mask, which should achieve the desired effect in
reconfigure_super() on this line:

	WRITE_ONCE(sb->s_flags, ((sb->s_flags & ~fc->sb_flags_mask) |
				 (fc->sb_flags & fc->sb_flags_mask)));

David