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

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Message-ID: <21c53d3f-5ca9-886d-a326-cb6f1bbddffd@sandeen.net>
Date:   Mon, 18 Sep 2017 17:00:58 -0500
From:   Eric Sandeen <sandeen@...deen.net>
To:     Dave Chinner <david@...morbit.com>, Jens Axboe <axboe@...nel.dk>
Cc:     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 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?

-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.
>