linux-kernel - Re: [linux-next][XFS][trinity] WARNING: CPU: 32 PID: 31369 at fs/iomap.c:993

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Message-ID: <20170918220412.GB6533@magnolia>
Date:   Mon, 18 Sep 2017 15:04:12 -0700
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Eric Sandeen <sandeen@...deen.net>
Cc:     Dave Chinner <david@...morbit.com>, Jens Axboe <axboe@...nel.dk>,
        Christoph Hellwig <hch@....de>,
        Abdul Haleem <abdhalee@...ux.vnet.ibm.com>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        linux-next <linux-next@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        chandan <chandan@...ux.vnet.ibm.com>
Subject: Re: [linux-next][XFS][trinity] WARNING: CPU: 32 PID: 31369 at
 fs/iomap.c:993

On Mon, Sep 18, 2017 at 05:00:58PM -0500, Eric Sandeen wrote:
> On 9/18/17 4:31 PM, Dave Chinner wrote:
> > On Mon, Sep 18, 2017 at 09:28:55AM -0600, Jens Axboe wrote:
> >> On 09/18/2017 09:27 AM, Christoph Hellwig wrote:
> >>> On Mon, Sep 18, 2017 at 08:26:05PM +0530, Abdul Haleem wrote:
> >>>> Hi,
> >>>>
> >>>> A warning is triggered from:
> >>>>
> >>>> file fs/iomap.c in function iomap_dio_rw
> >>>>
> >>>>     if (ret)
> >>>>         goto out_free_dio;
> >>>>
> >>>>     ret = invalidate_inode_pages2_range(mapping,
> >>>>             start >> PAGE_SHIFT, end >> PAGE_SHIFT);
> >>>>>>  WARN_ON_ONCE(ret);
> >>>>     ret = 0;
> >>>>
> >>>>     inode_dio_begin(inode);
> >>>
> >>> This is expected and an indication of a problematic workload - which
> >>> may be triggered by a fuzzer.
> >>
> >> If it's expected, why don't we kill the WARN_ON_ONCE()? I get it all
> >> the time running xfstests as well.
> > 
> > Because when a user reports a data corruption, the only evidence we
> > have that they are running an app that does something stupid is this
> > warning in their syslogs.  Tracepoints are not useful for replacing
> > warnings about data corruption vectors being triggered.
> 
> Is the full WARN_ON spew really helpful to us, though?  Certainly
> the user has no idea what it means, and will come away terrified
> but none the wiser.
> 
> Would a more informative printk_once() still give us the evidence
> without the ZOMG I THINK I OOPSED that a WARN_ON produces?  Or do we 
> want/need the backtrace?

Maybe we could state a little more directly what's going on:

if (err)
	printk_once(KERN_INFO "Urk, collision detected between direct IO and page cache, YHL. HAND.\n"); ?

8-)

--D

> 
> -Eric
> 
> > It needs to be on by default, bu tI'm sure we can wrap it with
> > something like an xfs_alert_tag() type of construct so the tag can
> > be set in /proc/fs/xfs/panic_mask to suppress it if testers so
> > desire.
> > 
> > Cheers,
> > 
> > Dave.
> > 
> --
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