Re: block: fix q->flush_rq NULL pointer crash on dm-mpath flush

[Jens Axboe]

On 2014-03-08 17:57, Mike Snitzer wrote:
> On Sat, Mar 08 2014 at  7:24pm -0500,
> Jens Axboe <axboe@xxxxxxxxx> wrote:
>
> > On 2014-03-08 15:09, Mike Snitzer wrote:
> > > On Sat, Mar 08 2014 at  4:33pm -0500,
> > > Hannes Reinecke <hare@xxxxxxx> wrote:
> > >
> > > > On 03/08/2014 07:13 PM, Mike Snitzer wrote:
> > > > > I'm calm.. was just a bit frustrated.  But this isn't a big deal.
> > > > > I'll make an effort to reach out to relevant people sooner when
> > > > > similar stuff is reported against recently upstreamed code.  Would be
> > > > > cool if you did the same.  I can relate to needing to have the distro
> > > > > vendor hat on (first needing to determine/answer "is this issue
> > > > > specific to our hacked distro kernel?", etc).
> > > > The patch I made wasn't in the context of 'recently upstreamed
> > > > code', it was due to a backport Jan Kara did for our next distro
> > > > kernels (3.12-based).
> > >
> > > "3.12-based" means nothing given all the backporting for SLES, much like
> > > "3.10-based" means nothing in the context of RHEL7.
> > >
> > > The only way this fix is applicable is in the context of "recently
> > > upstreamed code", commit 1874198 ("blk-mq: rework flush sequencing
> > > logic") went upstream for v3.14-rc3.
> > >
> > > Jens, please feel free to queue this tested fix for 3.14-rc:
> >
> > Thanks Mike, queued up.
>
> Thanks.
>
> > Also queued up the list addition reversal change.
>
> I had a look at what you queued, thing is commit 1874198 replaced code
> in blk_kick_flush() that did use list_add_tail().  So getting back to
> the way the original code  was (before 1874198) would need something
> like the following patch.
>
> But it isn't clear to me why we'd have the duality of front vs tail
> additions for flushes.  Maybe Christoph knows?

Not sure it'd even make a difference with the use case, but always tail 
would be broken. But the flushing in general is a bit of a nightmare, so 
I'd be inclined to add your full fix too, at least this late in -rc.

--
Jens Axboe

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/