Re: [Xen-devel] [linux-3.14 bisection] complete test-amd64-i386-xl-qcow2

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Ian Campbell writes ("Re: [linux-3.14 bisection] complete 
test-amd64-i386-xl-qcow2"):
> On Wed, 2015-08-26 at 20:02 +0000, osstest service owner wrote:
> >   commit 9e6c072a69d87100808d16279d60e9f857291340
> >   Author: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
> >   Date:   Fri Jun 26 03:28:24 2015 +0200
> >   
> >       xen/gntdevt: Fix race condition in gntdev_release()
> 
> I'm not sure what to make of this.
> 
> The qcow2 test is one of the only ones I'd expect to be exercising gntdev
> (most tests use LVM+blkback), which explains why this particular commit is
> apparently seeing issues due to this particular change.

(You mean `which explains why this particular _test_ is [failing]',
I think.)

The host serial log in one of the confirmation tests of 9e6c072a shows
serious trouble:

 
http://logs.test-lab.xenproject.org/osstest/logs/60893/test-amd64-i386-xl-qcow2/serial-huxelrebe1.log

 Aug 26 19:36:51.841068 [  738.050547] BUG: unable to handle kernel
 NULL pointer dereference at 00000014

 Aug 26 19:36:56.753068 [  738.050594] IP: [<c11829d3>]
 __mmu_notifier_invalidate_range_start+0x33/0x70

And the immediately preceding confirmation flight, which got a pass on
9e6c072a~1, seems fine:

 
http://logs.test-lab.xenproject.org/osstest/logs/60892/test-amd64-i386-xl-qcow2/serial-huxelrebe1.log

But, it's difficult to see how that gntdev fix would be responsible
for the bug.  Perhaps it changes the order in which certain things
happen so as to expose another bug.

Ian.

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