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From:   Olga Kornievskaia <aglo@umich.edu>
Date:   Wed, 10 Aug 2022 20:50:12 -0400
Message-ID: <CAN-5tyFLDrUMaTTi8ECTrKkAxxSdXGPEweGj8sQk5yW-vkmJ5g@mail.gmail.com>
Subject: help with nfsd kernel oops
To:     Chuck Lever <chuck.lever@oracle.com>,
        Jeff Layton <jlayton@kernel.org>
Cc:     linux-nfs <linux-nfs@vger.kernel.org>
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Hi folks (Chuck/Jeff specifically),

We've had this outstanding kernel oops that happens (infrequently) in
copy_offload testing (stack trace in the end). I've been trying to
debug it for a while, added printks and such. I can hand-wavey explain
what I'm seeing but I need help (a) nailing down exactly the problem
and (b) get a helpful hint how to address it?

Ok so what happens. Test case: source file is opened, locked,
(blah-blah destination file), copy_notify to the source server, copy
is done (src dest), source file unlocked (etc dest file), files
closed. Copy/Copy_notify, uses a locking stateid.

When unlocking happens it triggers LOCKU and FREE_STATEID. Copy_notify
stateid is associated with the locking stateid on the server. When the
last reference on the locking stateid goes nfs4_put_stateid() also
calls nfs4_free_cpntf_statelist() which deals with cleaning up the
copy_notify stateid.

In the laundry thread, there is a failsafe that if for some reason the
copy_notify state was not cleaned up/expired, then it would be deleted
there.

However in the failing case, where everything should be cleaned up as
it's supposed to be, instead I see calling to put_ol_stateid_locked()
(before FREE_STATEID is processed) which cleans up the parent but
doesn't touch the copy_notify stateids so instead the laundry thread
runs and walks the copy_notify list (since it's not empty) and tries
to free the entries but that leads to this oops (since part of the
memory was freed by put_ol_stateid_locked() and parent stateid)?.

Perhaps the fix is to add the  nfs4_free_cpntf_statelist() to
put_ol_stateid_locked() which I tried and it seems to work. But I'm
not confident about it.

Thoughts?

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index fa67ecd5fe63..b988d3c4e5fd 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -1408,6 +1408,7 @@ static void put_ol_stateid_locked(struct
nfs4_ol_stateid *stp,
        }

        idr_remove(&clp->cl_stateids, s->sc_stateid.si_opaque.so_id);
+       nfs4_free_cpntf_statelist(clp->net, s);
        list_add(&stp->st_locks, reaplist);
 }


[  338.681529] ------------[ cut here ]------------
[  338.683090] kernel BUG at lib/list_debug.c:53!
[  338.684372] invalid opcode: 0000 [#1] PREEMPT SMP KASAN PTI
[  338.685977] CPU: 1 PID: 493 Comm: kworker/u256:27 Tainted: G    B
          5.19.0-rc6+ #104
[  338.688266] Hardware name: VMware, Inc. VMware Virtual
Platform/440BX Desktop Reference Platform, BIOS 6.00 11/12/2020
[  338.691019] Workqueue: nfsd4 laundromat_main [nfsd]
[  338.692224] RIP: 0010:__list_del_entry_valid.cold.3+0x3d/0x53
[  338.693626] Code: 0b 4c 89 e1 4c 89 ee 48 c7 c7 e0 1a e3 8f e8 5b
60 fe ff 0f 0b 48 89 e9 4c 89 ea 48 89 de 48 c7 c7 60 1a e3 8f e8 44
60 fe ff <0f> 0b 48 89 ea 48 89 de 48 c7 c7 00 1a e3 8f e8 30 60 fe ff
0f 0b
[  338.697651] RSP: 0018:ffff88800d03fc68 EFLAGS: 00010286
[  338.698762] RAX: 000000000000006d RBX: ffff888028a14798 RCX: 0000000000000000
[  338.700442] RDX: 0000000000000000 RSI: dffffc0000000000 RDI: ffffffff917e9240
[  338.702257] RBP: ffff88801bb0ae90 R08: ffffed100a795f0e R09: ffffed100a795f0e
[  338.704016] R10: ffff888053caf86b R11: ffffed100a795f0d R12: ffff88801bb0ae90
[  338.705703] R13: d9c0013300000a39 R14: 000000000000005a R15: ffff88801b9f5800
[  338.707510] FS:  0000000000000000(0000) GS:ffff888053c80000(0000)
knlGS:0000000000000000
[  338.709319] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  338.710715] CR2: 00005640baab74d0 CR3: 0000000017574005 CR4: 00000000001706e0
[  338.712282] Call Trace:
[  338.712898]  <TASK>
[  338.713430]  _free_cpntf_state_locked+0x6b/0x120 [nfsd]
[  338.714806]  nfs4_laundromat+0x8ef/0xf30 [nfsd]
[  338.716013]  ? dequeue_entity+0x18b/0x6c0
[  338.716970]  ? release_lock_stateid+0x60/0x60 [nfsd]
[  338.718169]  ? _raw_spin_unlock+0x15/0x30
[  338.719064]  ? __switch_to+0x2fa/0x690
[  338.719879]  ? __schedule+0x67d/0xf20
[  338.720678]  laundromat_main+0x15/0x40 [nfsd]
[  338.721760]  process_one_work+0x3b4/0x6b0
[  338.722629]  worker_thread+0x5a/0x640
[  338.723425]  ? process_one_work+0x6b0/0x6b0
[  338.724324]  kthread+0x162/0x190
[  338.725030]  ? kthread_complete_and_exit+0x20/0x20
[  338.726074]  ret_from_fork+0x22/0x30
[  338.726856]  </TASK>