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From:   Chuck Lever III <chuck.lever@oracle.com>
To:     Olga Kornievskaia <aglo@umich.edu>
CC:     Jeff Layton <jlayton@kernel.org>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Subject: Re: Is this nfsd kernel oops known?
Thread-Topic: Is this nfsd kernel oops known?
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> On Sep 1, 2022, at 9:51 AM, Olga Kornievskaia <aglo@umich.edu> wrote:
>=20
> On Tue, Aug 30, 2022 at 1:49 PM Jeff Layton <jlayton@kernel.org> wrote:
>>=20
>> On Tue, 2022-08-30 at 13:14 -0400, Olga Kornievskaia wrote:
>>> Hi folks,
>>>=20
>>> Is this a known nfsd kernel oops in 6.0-rc1. Was running xfstests on
>>> pre-rhel-9.1 client against 6.0-rc1 server when it panic-ed.
>>>=20
>>> [ 5554.769159] BUG: KASAN: null-ptr-deref in kernel_sendpage+0x60/0x220
>>> [ 5554.770526] Read of size 8 at addr 0000000000000008 by task nfsd/259=
0
>>> [ 5554.771899]
>>=20
>> No, I haven't seen this one. I'm guessing the page pointer passed to
>> kernel_sendpage was probably NULL, so this may be a case where something
>> walked off the end of the rq_pages array?
>>=20
>> Beyond that I can't tell much from just this stack trace. It might be
>> nice to see what line of code kernel_sendpage+0x60 refers to on your
>> kernel.
>=20
> After getting debug symbols this is what gdb told me...
>=20
> (gdb) l *(kernel_sendpage+0x60)
> 0xffffffff81cbd570 is in kernel_sendpage (./include/linux/page-flags.h:48=
7).
> 482 TESTCLEARFLAG(LRU, lru, PF_HEAD)
> 483 PAGEFLAG(Active, active, PF_HEAD) __CLEARPAGEFLAG(Active, active, PF_=
HEAD)
> 484 TESTCLEARFLAG(Active, active, PF_HEAD)
> 485 PAGEFLAG(Workingset, workingset, PF_HEAD)
> 486 TESTCLEARFLAG(Workingset, workingset, PF_HEAD)
> 487 __PAGEFLAG(Slab, slab, PF_NO_TAIL)
> 488 __PAGEFLAG(SlobFree, slob_free, PF_NO_TAIL)
> 489 PAGEFLAG(Checked, checked, PF_NO_COMPOUND)   /* Used by some filesyst=
ems */
> 490
> 491 /* Xen */
>=20
> I'm unable to complete a git bisect. Could somebody suggest what to do
> when a git bisect midpoint results in an unbootable kernel? I can't
> "skip" this point can I? I'm not sure if marking it "bad" makes sense
> since it's not relevant to the actual problem.

Try skipping. I think "git bisect" is supposed to be smart enough
to figure things out after a skip.

If not, start over and pick endpoints that you think might avoid
the unbootable kernels. Even adjusting one endpoint a little
might be enough to make bisect pick new targets that avoid the
unbootable kernels.


--
Chuck Lever