linux-kernel - Re: [PATCH RFC 3/2] fstests: check that we can't write to swap files

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Message-Id: <20190815142603.de9f1c0d9fcc017f3237708d@linux-foundation.org>
Date:   Thu, 15 Aug 2019 14:26:03 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     "Darrick J. Wong" <darrick.wong@...cle.com>
Cc:     hch@...radead.org, tytso@....edu, viro@...iv.linux.org.uk,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        fstests <fstests@...r.kernel.org>
Subject: Re: [PATCH RFC 3/2] fstests: check that we can't write to swap
 files

On Thu, 15 Aug 2019 09:34:34 -0700 "Darrick J. Wong" <darrick.wong@...cle.com> wrote:

> While active, the media backing a swap file is leased to the kernel.
> Userspace has no business writing to it.  Make sure we can't do this.

I don't think this tests the case where a file was already open for
writing and someone does swapon(that file)?

And then does swapoff(that file), when writes should start working again?

Ditto all the above, with s/open/mmap/.

Do we handle (and test!) the case where there's unwritten dirty
pagecache at the time of swapon()?  Ditto pte-dirty MAP_SHARED pages?