Re: SG does not ignore dxferp (direct io + mmap)

[Laurence Oberman <loberman@redhat.com>]

----- Original Message -----
> From: "Hannes Reinecke" <hare@suse.de>
> To: emilne@redhat.com, "Christoph Hellwig" <hch@infradead.org>
> Cc: "Martin K. Petersen" <martin.petersen@oracle.com>, "Johannes Thumshirn" <jthumshirn@suse.de>, "Laurence Oberman"
> <loberman@redhat.com>, "Eyal Ben David" <bdeyal@gmail.com>, dgilbert@interlog.com, linux-scsi@vger.kernel.org
> Sent: Friday, December 2, 2016 9:10:01 AM
> Subject: Re: SG does not ignore dxferp (direct io + mmap)
> 
> On 12/02/2016 02:29 PM, Ewan D. Milne wrote:
> > On Fri, 2016-12-02 at 04:21 -0800, Christoph Hellwig wrote:
> >> On Thu, Dec 01, 2016 at 08:40:31AM -0500, Martin K. Petersen wrote:
> >>> Specifically, the problem appears to be caused by the removal of
> >>> the setting of bio->bi_bdev, which would previously be set to NULL.
> >>> If I add:
> >>
> >> Very odd.  For one I would expect it to be NULL anyway, second
> >> I don't see why the behavior changed.  But given that this reverts
> >> to the original assignment and makes things work I'll happily hack it
> >> to get things working again:
> >>
> >> Acked-by: Christoph Hellwig <hch@lst.de>
> >
> > Yeah, I'm not sure I understand this either, apart from the change
> > adjusting the code to effectively do what it used to and making the
> > test case work.  I'm reluctant to cc: stable yet, let me look at this
> > a bit more and I'll post the actual patch soon.
> >
> Plus we found that this is basically a timing issue; we've found that
> supposedly fixed bugs will crop up after ~4k iterations.
> (Johannes did a _lot_ of testing here :-)
> So just because the bug failed to materialize can also mean that you
> simply didn't test long enough.
> 
> Cheers,
> 
> Hannes
> --
> Dr. Hannes Reinecke		   Teamlead Storage & Networking
> hare@suse.de			               +49 911 74053 688
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> 
Hannes, 
Just to clarify, my original test reverting  commit 3fa6c507319c897598512da91c010a4ad2ed682c,
what Ewan originally bisected to and running > 100000 iterations never failed.