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Message-ID: <20181017161906.GA5096@infradead.org>
Date: Wed, 17 Oct 2018 09:19:06 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Daniel Colascione <dancol@...gle.com>
Cc: Christoph Hellwig <hch@...radead.org>,
Joel Fernandes <joel@...lfernandes.org>,
linux-kernel <linux-kernel@...r.kernel.org>,
kernel-team@...roid.com, John Reck <jreck@...gle.com>,
John Stultz <john.stultz@...aro.org>,
Todd Kjos <tkjos@...gle.com>,
Greg KH <gregkh@...uxfoundation.org>,
Andrew Morton <akpm@...ux-foundation.org>,
"J. Bruce Fields" <bfields@...ldses.org>,
Jeff Layton <jlayton@...nel.org>,
Khalid Aziz <khalid.aziz@...cle.com>,
linux-fsdevel@...r.kernel.org, linux-kselftest@...r.kernel.org,
linux-mm <linux-mm@...ck.org>,
Mike Kravetz <mike.kravetz@...cle.com>,
Minchan Kim <minchan@...gle.com>, Shuah Khan <shuah@...nel.org>
Subject: Re: [PATCH v2 1/2] mm: Add an F_SEAL_FS_WRITE seal to memfd
On Wed, Oct 17, 2018 at 08:44:01AM -0700, Daniel Colascione wrote:
> > Even if no one changes these specific flags we still need a lock due
> > to rmw cycles on the field. For example fadvise can set or clear
> > FMODE_RANDOM. It seems to use file->f_lock for synchronization.
>
> Compare-and-exchange will suffice, right?
Only if all users use the compare and exchange, and right now they
don't.
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