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From:   Chuck Lever III <chuck.lever@oracle.com>
To:     Jeff Layton <jlayton@kernel.org>
CC:     Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Subject: Re: oops in nfsd-next branch
Thread-Topic: oops in nfsd-next branch
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Date:   Thu, 20 Jul 2023 15:29:58 +0000
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> On Jul 20, 2023, at 10:33 AM, Jeff Layton <jlayton@kernel.org> wrote:
>=20
> On Wed, 2023-07-19 at 23:46 +0000, Chuck Lever III wrote:
>>=20
>>> On Jul 19, 2023, at 5:48 PM, Jeff Layton <jlayton@kernel.org> wrote:
>>>=20
>>> Hi Chuck,
>>>=20
>>> While doing some testing today with pynfs on a branch based on your
>>> nfsd-next branch. I'm not sure which test triggers it, but it's one of
>>> the v4.0 tests.
>>=20
>> I've just started running pynfs on nfsd-next, haven't seen any
>> crashes so far. I'll take a dive in tomorrow.
>>=20
>>=20
>>> It only takes a few mins before it crashes:
>>>=20
>>> Jul 19 19:22:43 kdevops-nfsd kernel: BUG: unable to handle page fault f=
or address: ffffd8442d049108
>>> Jul 19 19:22:43 kdevops-nfsd kernel: #PF: supervisor read access in ker=
nel mode
>>> Jul 19 19:22:43 kdevops-nfsd kernel: #PF: error_code(0x0000) - not-pres=
ent page
>>> Jul 19 19:22:43 kdevops-nfsd kernel: PGD 0 P4D 0=20
>>> Jul 19 19:22:43 kdevops-nfsd kernel: Oops: 0000 [#1] PREEMPT SMP PTI
>>> Jul 19 19:22:43 kdevops-nfsd kernel: CPU: 0 PID: 743 Comm: nfsd Not tai=
nted 6.5.0-rc2+ #19
>>> Jul 19 19:22:43 kdevops-nfsd kernel: Hardware name: QEMU Standard PC (Q=
35 + ICH9, 2009), BIOS 1.16.2-1.fc38 04/01/2014
>>> Jul 19 19:22:43 kdevops-nfsd kernel: RIP: 0010:kfree+0x4b/0x110
>>> Jul 19 19:22:43 kdevops-nfsd kernel: Code: 80 48 01 d8 0f 82 d8 00 00 0=
0 48 c7 c2 00 00 00 80 48 2b 15 9f d7 fb 00 48 01 d0 48 c1 e8 0c 48 c1 e0 0=
6 48 03 05 7d d7 fb 00 <48> 8b 50 08 48 89 c7 f6 c2 01 0f 85 9f 00 00 >
>>> Jul 19 19:22:43 kdevops-nfsd kernel: RSP: 0018:ffffb0858661bdc0 EFLAGS:=
 00010286
>>> Jul 19 19:22:43 kdevops-nfsd kernel: RAX: ffffd8442d049100 RBX: 0000000=
081244052 RCX: ffff8a665e003008
>>> Jul 19 19:22:43 kdevops-nfsd kernel: RDX: 0000759a40000000 RSI: fffffff=
fc0b13a45 RDI: 0000000081244052
>>> Jul 19 19:22:43 kdevops-nfsd kernel: RBP: ffffb0858661be40 R08: ffff8a6=
65e003008 R09: ffffffff8ebdc4ec
>>> Jul 19 19:22:43 kdevops-nfsd kernel: R10: 000000000000000e R11: 0000000=
00000001b R12: ffff8a6656f20150
>>> Jul 19 19:22:43 kdevops-nfsd kernel: R13: ffff8a665e003008 R14: ffff8a6=
656f20100 R15: ffff8a6656f20980
>>> Jul 19 19:22:43 kdevops-nfsd kernel: FS:  0000000000000000(0000) GS:fff=
f8a67bfc00000(0000) knlGS:0000000000000000
>>> Jul 19 19:22:43 kdevops-nfsd kernel: CS:  0010 DS: 0000 ES: 0000 CR0: 0=
000000080050033
>>> Jul 19 19:22:43 kdevops-nfsd kernel: CR2: ffffd8442d049108 CR3: 0000000=
277e1a001 CR4: 0000000000060ef0
>>> Jul 19 19:22:43 kdevops-nfsd kernel: Call Trace:
>>> Jul 19 19:22:43 kdevops-nfsd kernel:  <TASK>
>>> Jul 19 19:22:43 kdevops-nfsd kernel:  ? __die+0x1f/0x70
>>> Jul 19 19:22:43 kdevops-nfsd kernel:  ? page_fault_oops+0x159/0x450
>>> Jul 19 19:22:43 kdevops-nfsd kernel:  ? fixup_exception+0x22/0x310
>>> Jul 19 19:22:43 kdevops-nfsd kernel:  ? exc_page_fault+0x157/0x180
>>> Jul 19 19:22:43 kdevops-nfsd kernel:  ? asm_exc_page_fault+0x22/0x30
>>> Jul 19 19:22:43 kdevops-nfsd kernel:  ? nfsd_cache_lookup+0x3c5/0x770 [=
nfsd]
>>> Jul 19 19:22:43 kdevops-nfsd kernel:  ? kfree+0x4b/0x110
>>> Jul 19 19:22:43 kdevops-nfsd kernel:  nfsd_cache_lookup+0x3c5/0x770 [nf=
sd]
>>> Jul 19 19:22:43 kdevops-nfsd kernel:  ? __pfx_nfsd+0x10/0x10 [nfsd]
>>> Jul 19 19:22:43 kdevops-nfsd kernel:  nfsd_dispatch+0x62/0x1b0 [nfsd]
>>> Jul 19 19:22:43 kdevops-nfsd kernel:  svc_process_common+0x3cb/0x6c0 [s=
unrpc]
>>> Jul 19 19:22:43 kdevops-nfsd kernel:  ? __pfx_nfsd_dispatch+0x10/0x10 [=
nfsd]
>>> Jul 19 19:22:43 kdevops-nfsd kernel:  ? __pfx_nfsd+0x10/0x10 [nfsd]
>>> Jul 19 19:22:43 kdevops-nfsd kernel:  svc_process+0x12d/0x170 [sunrpc]
>>> Jul 19 19:22:43 kdevops-nfsd kernel:  nfsd+0xd5/0x1a0 [nfsd]
>>> Jul 19 19:22:43 kdevops-nfsd kernel:  kthread+0xf3/0x120
>>> Jul 19 19:22:43 kdevops-nfsd kernel:  ? __pfx_kthread+0x10/0x10
>>> Jul 19 19:22:43 kdevops-nfsd kernel:  ret_from_fork+0x30/0x50
>>> Jul 19 19:22:43 kdevops-nfsd kernel:  ? __pfx_kthread+0x10/0x10
>>> Jul 19 19:22:43 kdevops-nfsd kernel:  ret_from_fork_asm+0x1b/0x30
>>> Jul 19 19:22:43 kdevops-nfsd kernel: RIP: 0000:0x0
>>> Jul 19 19:22:43 kdevops-nfsd kernel: Code: Unable to access opcode byte=
s at 0xffffffffffffffd6.
>>> Jul 19 19:22:43 kdevops-nfsd kernel: RSP: 0000:0000000000000000 EFLAGS:=
 00000000 ORIG_RAX: 0000000000000000
>>> Jul 19 19:22:43 kdevops-nfsd kernel: RAX: 0000000000000000 RBX: 0000000=
000000000 RCX: 0000000000000000
>>> Jul 19 19:22:43 kdevops-nfsd kernel: RDX: 0000000000000000 RSI: 0000000=
000000000 RDI: 0000000000000000
>>> Jul 19 19:22:43 kdevops-nfsd kernel: RBP: 0000000000000000 R08: 0000000=
000000000 R09: 0000000000000000
>>> Jul 19 19:22:43 kdevops-nfsd kernel: R10: 0000000000000000 R11: 0000000=
000000000 R12: 0000000000000000
>>> Jul 19 19:22:43 kdevops-nfsd kernel: R13: 0000000000000000 R14: 0000000=
000000000 R15: 0000000000000000
>>> Jul 19 19:22:43 kdevops-nfsd kernel:  </TASK>
>>> Jul 19 19:22:43 kdevops-nfsd kernel: Modules linked in: 9p netfs nls_is=
o8859_1 nls_cp437 vfat fat kvm_intel joydev kvm cirrus psmouse drm_shmem_he=
lper irqbypass pcspkr virtio_net net_failover failover virtio_balloon >
>>> Jul 19 19:22:43 kdevops-nfsd kernel: CR2: ffffd8442d049108
>>> Jul 19 19:22:43 kdevops-nfsd kernel: ---[ end trace 0000000000000000 ]-=
--
>>> Jul 19 19:22:43 kdevops-nfsd kernel: RIP: 0010:kfree+0x4b/0x110
>>> Jul 19 19:22:43 kdevops-nfsd kernel: Code: 80 48 01 d8 0f 82 d8 00 00 0=
0 48 c7 c2 00 00 00 80 48 2b 15 9f d7 fb 00 48 01 d0 48 c1 e8 0c 48 c1 e0 0=
6 48 03 05 7d d7 fb 00 <48> 8b 50 08 48 89 c7 f6 c2 01 0f 85 9f 00 00 >
>>> Jul 19 19:22:43 kdevops-nfsd kernel: RSP: 0018:ffffb0858661bdc0 EFLAGS:=
 00010286
>>> Jul 19 19:22:43 kdevops-nfsd kernel: RAX: ffffd8442d049100 RBX: 0000000=
081244052 RCX: ffff8a665e003008
>>> Jul 19 19:22:43 kdevops-nfsd kernel: RDX: 0000759a40000000 RSI: fffffff=
fc0b13a45 RDI: 0000000081244052
>>> Jul 19 19:22:43 kdevops-nfsd kernel: RBP: ffffb0858661be40 R08: ffff8a6=
65e003008 R09: ffffffff8ebdc4ec
>>> Jul 19 19:22:43 kdevops-nfsd kernel: R10: 000000000000000e R11: 0000000=
00000001b R12: ffff8a6656f20150
>>> Jul 19 19:22:43 kdevops-nfsd kernel: R13: ffff8a665e003008 R14: ffff8a6=
656f20100 R15: ffff8a6656f20980
>>> Jul 19 19:22:43 kdevops-nfsd kernel: FS:  0000000000000000(0000) GS:fff=
f8a67bfc00000(0000) knlGS:0000000000000000
>>> Jul 19 19:22:43 kdevops-nfsd kernel: CS:  0010 DS: 0000 ES: 0000 CR0: 0=
000000080050033
>>> Jul 19 19:22:43 kdevops-nfsd kernel: CR2: ffffffffffffffd6 CR3: 0000000=
277e1a001 CR4: 0000000000060ef0
>>> Jul 19 19:22:43 kdevops-nfsd kernel: note: nfsd[743] exited with irqs d=
isabled
>>> Jul 19 19:22:43 kdevops-nfsd kernel: note: nfsd[743] exited with preemp=
t_count 1
>>>=20
>>> faddr2line says:
>>>=20
>>> $ ./scripts/faddr2line --list fs/nfsd/nfsd.ko nfsd_cache_lookup+0x3c5/0=
x770
>>> nfsd_cacherep_free at /home/jlayton/git/kdevops/linux/fs/nfsd/nfscache.=
c:116
>>> 111 }
>>> 112=20
>>> 113 static void nfsd_cacherep_free(struct nfsd_cacherep *rp)
>>> 114 {
>>> 115 kfree(rp->c_replvec.iov_base);
>>>> 116< kmem_cache_free(drc_slab, rp);
>>> 117 }
>>> 118=20
>>> 119 static unsigned long
>>> 120 nfsd_cacherep_dispose(struct list_head *dispose)
>>> 121 {
>>>=20
>>> (inlined by) nfsd_reply_cache_free_locked at /home/jlayton/git/kdevops/=
linux/fs/nfsd/nfscache.c:153
>>> 148 static void
>>> 149 nfsd_reply_cache_free_locked(struct nfsd_drc_bucket *b, struct nfsd=
_cacherep *rp,
>>> 150 struct nfsd_net *nn)
>>> 151 {
>>> 152 nfsd_cacherep_unlink_locked(nn, b, rp);
>>>> 153< nfsd_cacherep_free(rp);
>>> 154 }
>>> 155=20
>>> 156 static void
>>> 157 nfsd_reply_cache_free(struct nfsd_drc_bucket *b, struct nfsd_cacher=
ep *rp,
>>> 158 struct nfsd_net *nn)
>>>=20
>>> (inlined by) nfsd_cache_lookup at /home/jlayton/git/kdevops/linux/fs/nf=
sd/nfscache.c:527
>>> 522 nfsd_stats_drc_mem_usage_add(nn, sizeof(*rp));
>>> 523 goto out;
>>> 524=20
>>> 525 found_entry:
>>> 526 /* We found a matching entry which is either in progress or done. *=
/
>>>> 527< nfsd_reply_cache_free_locked(NULL, rp, nn);
>>> 528 nfsd_stats_rc_hits_inc();
>>> 529 rtn =3D RC_DROPIT;
>>> 530 rp =3D found;
>>> 531=20
>>> 532 /* Request being processed */
>>>=20
>>>=20
>>> ...and a bisect landed here:
>>>=20
>>>=20
>>> 767b1d5badd6eb418e3f91f0cd8fa6d2894ff43a is the first bad commit
>>> commit 767b1d5badd6eb418e3f91f0cd8fa6d2894ff43a
>>> Author: Chuck Lever <chuck.lever@oracle.com>
>>> Date:   Sun Jul 9 11:45:16 2023 -0400
>>>=20
>>>   NFSD: Refactor nfsd_reply_cache_free_locked()
>>>=20
>>>   To reduce contention on the bucket locks, we must avoid calling
>>>   kfree() while each bucket lock is held.
>>>=20
>>>   Start by refactoring nfsd_reply_cache_free_locked() into a helper
>>>   that removes an entry from the bucket (and must therefore run under
>>>   the lock) and a second helper that frees the entry (which does not
>>>   need to hold the lock).
>>>=20
>>>   For readability, rename the helpers nfsd_cacherep_<verb>.
>>>=20
>>>   Reviewed-by: Jeff Layton <jlayton@kernel.org>
>>>   Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
>>>=20
>>> fs/nfsd/nfscache.c | 26 +++++++++++++++++++-------
>>> 1 file changed, 19 insertions(+), 7 deletions(-)
>>>=20
>>> --=20
>>> Jeff Layton <jlayton@kernel.org>
>>=20
>=20
> So far, it seems to be surviving with this patch on top. c_replvec is
> part of a union, so you need to ensure it actually holds a kvec.
>=20
>=20
> diff --git a/fs/nfsd/nfscache.c b/fs/nfsd/nfscache.c
> index 6eb3d7bdfaf3..80621a709510 100644
> --- a/fs/nfsd/nfscache.c
> +++ b/fs/nfsd/nfscache.c
> @@ -112,7 +112,8 @@ nfsd_cacherep_alloc(struct svc_rqst *rqstp, __wsum cs=
um,
>=20
> static void nfsd_cacherep_free(struct nfsd_cacherep *rp)
> {
> - kfree(rp->c_replvec.iov_base);
> + if (rp->c_type =3D=3D RC_REPLBUFF)
> + kfree(rp->c_replvec.iov_base);
> kmem_cache_free(drc_slab, rp);
> }

Agreed, that was an unintended change to the logic introduced by
that commit, and it lines up with the RIP.


--
Chuck Lever