Re: mips qemu test failures in -next due to "kthread: Fix use-after-free if kthread fork fails"

[Guenter Roeck]

+cc Linus, as mainline is now affected.

On 05/28/2017 04:45 AM, Vegard Nossum wrote:
> On 05/27/17 19:56, Guenter Roeck wrote:
> > Hi,
> >
> > my qemu testis of mips images are failing in -next. Symptom is a hang during
> > boot; see http://kerneltests.org/builders/qemu-mips-next for some examples.
> >
> > I bisected the problem in next-20170526. It points to commit 4d6501dce079c
> > ("kthread: Fix use-after-free if kthread fork fails"). Reverting that patch
> > fixes the problem.
> >
> > Bisect log is attached.
>
> Hi,
>
> Thanks for the report and sorry for the breakage :-/
>
> I can't immediately spot what's going wrong, but I am able to reproduce
> it on mips so I will try to debug.
>
> Are you sure it's this commit, though? I checked out linus/master and
> I get a boot hang even after reverting it.

Reverting the patch fixed the problem for me in -next. The last mainline build
on my test system was with v4.12-rc2-228-gc86daad, which was fine except for
the known build breakages (frv, hexagon) and the known tracebacks
in crisv32
	WARNING: CPU: 0 PID: 1 at drivers/mtd/mtdcore.c:734 mtd_device_parse_register+0x17a/0x1aa
and ppc
	refcount_t: underflow; use-after-free.
	WARNING: CPU: 0 PID: 1 at lib/refcount.c:184 refcount_sub_and_test+0x84/0xe0

It may well be that something else is broken in mainline. The build of
v4.12-rc2-284-g249f1ef on my builders isn't complete yet. We'll see in
a couple of hours if there is other damage. I'll bisect later today if
necessary.

Guenter