linux-kernel - Re: [btrfs] WARNING: CPU: 0 PID: 6379 at fs/direct-io.c:293 dio

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Date:   Tue, 14 Nov 2017 12:17:44 -0500
From:   Theodore Ts'o <tytso@....edu>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     "Darrick J. Wong" <darrick.wong@...cle.com>,
        Jens Axboe <axboe@...nel.dk>,
        Eric Biggers <ebiggers3@...il.com>,
        Eryu Guan <guaneryu@...il.com>,
        Fengguang Wu <fengguang.wu@...el.com>,
        Lukas Czerner <lczerner@...hat.com>, Jan Kara <jack@...e.cz>,
        Jeff Moyer <jmoyer@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        xfs <linux-xfs@...r.kernel.org>
Subject: Re: [btrfs] WARNING: CPU: 0 PID: 6379 at fs/direct-io.c:293
 dio_complete+0x1d4/0x220

On Mon, Nov 13, 2017 at 02:01:36PM -0800, Linus Torvalds wrote:
> 
> And in the end, maybe even the warning is pointless. You used
> direct-IO and cached IO at the same time, and you got coherency
> issues. What did you expect? directio is fundamentally broken.

A single warning per inode, "page cache coherency broken due to direct
I/O; userspace did a dumb thing; oh, well" is probably more than
sufficient.  The reason to have the warning is so that when the user
complains about the file system bug, we can point at the "userspace
did a dumb thing" warning message.

						- Ted