linux-kernel - Re: btrfs_direct

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Message-ID: <20161008232008.nouzkd54kiquvpir@codemonkey.org.uk>
Date:   Sat, 8 Oct 2016 19:20:08 -0400
From:   Dave Jones <davej@...emonkey.org.uk>
To:     Al Viro <viro@...IV.linux.org.uk>
Cc:     Chris Mason <clm@...com>, Josef Bacik <jbacik@...com>,
        David Sterba <dsterba@...e.com>, linux-btrfs@...r.kernel.org,
        Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: btrfs_direct_IO oops

On Sat, Oct 08, 2016 at 07:29:03PM +0100, Al Viro wrote:
 > On Sat, Oct 08, 2016 at 02:08:06PM -0400, Dave Jones wrote:
 > > That code: matches this dissembly:
 > > 
 > >                 for (i = seg + 1; i < iter->nr_segs; i++) {
 > 
 > *whoa*
 > 
 > OK, that loop in check_direct_IO() should be done *ONLY* for
 > iovec iter - even for a bvec one it's completely bogus, and
 > for pipe ones it blows up immediately.
 > 
 > Sorry, I'd missed that bogosity - replace
 >         if (iov_iter_rw(iter) == WRITE)
 > 		return 0;
 > with
 > 	if (iov_iter_rw(iter) != READ || !iter_is_iovec(iter))
 > 		return 0;
 > in there; that should fix the damn thing.

Yep, seems to do the trick. Have been running the last six hours
without seeing it or anything similar since.

	Dave