linux-kernel - Re: [PATCH 2/2] vfs: don't allow writes to swap files

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Message-ID: <20190816064858.GG15186@magnolia>
Date:   Thu, 15 Aug 2019 23:48:58 -0700
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     akpm@...ux-foundation.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
Subject: Re: [PATCH 2/2] vfs: don't allow writes to swap files

On Thu, Aug 15, 2019 at 11:41:21PM -0700, Christoph Hellwig wrote:
> The new checks look fine to me, but where does the inode_drain_writes()
> function come from, I can't find that in my tree anywhere.

Doh.  Forgot to include that patch in the series. :(

/*
 * Flush file data before changing attributes.  Caller must hold any locks
 * required to prevent further writes to this file until we're done setting
 * flags.
 */
static inline int inode_drain_writes(struct inode *inode)
{
       inode_dio_wait(inode);
       return filemap_write_and_wait(inode->i_mapping);
}

> Also what does inode_drain_writes do about existing shared writable
> mapping?  Do we even care about that corner case?

We probably ought to flush and invalidate the pagecache for the entire
file so that page_mkwrite can bounce off the swapfile.

--D