linux-ext4 - Re: always fall back to buffered I/O after invalidation failures, was: Re: [PATCH 2/6] iomap: IOMAP_DIO_RWF_NO_STALE_PAGECACHE return if page invalidation fails

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20200707125705.GK25523@casper.infradead.org>
Date:   Tue, 7 Jul 2020 13:57:05 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Goldwyn Rodrigues <rgoldwyn@...e.de>
Cc:     Christoph Hellwig <hch@....de>, linux-fsdevel@...r.kernel.org,
        linux-btrfs@...r.kernel.org, fdmanana@...il.com, dsterba@...e.cz,
        david@...morbit.com, darrick.wong@...cle.com,
        cluster-devel@...hat.com, linux-ext4@...r.kernel.org,
        linux-xfs@...r.kernel.org
Subject: Re: always fall back to buffered I/O after invalidation failures,
 was: Re: [PATCH 2/6] iomap: IOMAP_DIO_RWF_NO_STALE_PAGECACHE return if page
 invalidation fails

On Tue, Jul 07, 2020 at 07:43:46AM -0500, Goldwyn Rodrigues wrote:
> On  9:53 01/07, Christoph Hellwig wrote:
> > On Mon, Jun 29, 2020 at 02:23:49PM -0500, Goldwyn Rodrigues wrote:
> > > From: Goldwyn Rodrigues <rgoldwyn@...e.com>
> > > 
> > > For direct I/O, add the flag IOMAP_DIO_RWF_NO_STALE_PAGECACHE to indicate
> > > that if the page invalidation fails, return back control to the
> > > filesystem so it may fallback to buffered mode.
> > > 
> > > Reviewed-by: Darrick J. Wong <darrick.wong@...cle.com>
> > > Signed-off-by: Goldwyn Rodrigues <rgoldwyn@...e.com>
> > 
> > I'd like to start a discussion of this shouldn't really be the
> > default behavior.  If we have page cache that can't be invalidated it
> > actually makes a whole lot of sense to not do direct I/O, avoid the
> > warnings, etc.
> > 
> > Adding all the relevant lists.
> 
> Since no one responded so far, let me see if I can stir the cauldron :)
> 
> What error should be returned in case of such an error? I think the

Christoph's message is ambiguous.  I don't know if he means "fail the
I/O with an error" or "satisfy the I/O through the page cache".  I'm
strongly in favour of the latter.  Indeed, I'm in favour of not invalidating
the page cache at all for direct I/O.  For reads, I think the page cache
should be used to satisfy any portion of the read which is currently
cached.  For writes, I think we should write into the page cache pages
which currently exist, and then force those pages to be written back,
but left in cache.