On Tue, Jul 19, 2016 at 02:22:47PM -0700, Calvin Owens wrote:
> On 07/18/2016 07:05 PM, Calvin Owens wrote:
> >On 07/17/2016 11:02 PM, Dave Chinner wrote:
> >>On Sun, Jul 17, 2016 at 10:00:03AM +1000, Dave Chinner wrote:
> >>>On Fri, Jul 15, 2016 at 05:18:02PM -0700, Calvin Owens wrote:
> >>>>Hello all,
> >>>>
> >>>>I've found a nasty source of slab corruption. Based on seeing similar
> >>>>symptoms
> >>>>on boxes at Facebook, I suspect it's been around since at least 3.10.
> >>>>
> >>>>It only reproduces under memory pressure so far as I can tell: the issue
> >>>>seems
> >>>>to be that XFS reclaims pages from buffers that are still in use by
> >>>>scsi/block. I'm not sure which side the bug lies on, but I've only
> >>>>observed it
> >>>>with XFS.
> >>[....]
> >>>But this indicates that the page is under writeback at this point,
> >>>so that tends to indicate that the above freeing was incorrect.
> >>>
> >>>Hmmm - it's clear we've got direct reclaim involved here, and the
> >>>suspicion of a dirty page that has had it's bufferheads cleared.
> >>>Are there any other warnings in the log from XFS prior to kasan
> >>>throwing the error?
> >>
> >>Can you try the patch below?
> >
> >Thanks for getting this out so quickly :)
> >
> >So far so good: I booted Linus' tree as of this morning and reproduced the
> >ASAN
> >splat. After applying your patch I haven't triggered it.
> >
> >I'm a bit wary since it was hard to trigger reliably in the first place...
> >so I
> >lined up a few dozen boxes to run the test case overnight. I'll confirm in
> >the
> >morning (-0700) they look good.
>
> All right, my testcase ran 2099 times overnight without triggering anything.
>
> For the overnight tests, I booted the boxes with "mem=" to artificially limit
> RAM,
> which makes my repro *much* more reliable (I feel silly for not thinking of
> that
> in the first place). With that setup, I hit the ASAN splat 21 times in 98
> runs on
> vanilla 4.7-rc7. So I'm sold.
>
> Tested-by: Calvin Owens <calvinowens@xxxxxx>
Thanks for testing, Calvin. I'll update the patch and get it
reviewed and committed.
Cheers,
Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
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