Re: [bug report] kernel 5.18.0-rc4 oops with invalid wait context

[Chuck Lever III <chuck.lever@oracle.com>]

> On May 10, 2022, at 10:24 AM, Chuck Lever III <chuck.lever@oracle.com> wrote:
> 
> 
> 
>> On May 3, 2022, at 3:11 PM, dai.ngo@oracle.com wrote:
>> 
>> Hi,
>> 
>> I just noticed there were couple of oops in my Oracle6 in nfs4.dev network.
>> I'm not sure who ran which tests (be useful to know) that caused these oops.
>> 
>> Here is the stack traces:
>> 
>> [286123.154006] BUG: sleeping function called from invalid context at kernel/locking/rwsem.c:1585
>> [286123.155126] in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 3983, name: nfsd
>> [286123.155872] preempt_count: 1, expected: 0
>> [286123.156443] RCU nest depth: 0, expected: 0
>> [286123.156771] 1 lock held by nfsd/3983:
>> [286123.156786]  #0: ffff888006762520 (&clp->cl_lock){+.+.}-{2:2}, at: nfsd4_release_lockowner+0x306/0x850 [nfsd]
>> [286123.156949] Preemption disabled at:
>> [286123.156961] [<0000000000000000>] 0x0
>> [286123.157520] CPU: 1 PID: 3983 Comm: nfsd Kdump: loaded Not tainted 5.18.0-rc4+ #1
>> [286123.157539] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
>> [286123.157552] Call Trace:
>> [286123.157565]  <TASK>
>> [286123.157581]  dump_stack_lvl+0x57/0x7d
>> [286123.157609]  __might_resched.cold+0x222/0x26b
>> [286123.157644]  down_read_nested+0x68/0x420
>> [286123.157671]  ? down_write_nested+0x130/0x130
>> [286123.157686]  ? rwlock_bug.part.0+0x90/0x90
>> [286123.157705]  ? rcu_read_lock_sched_held+0x81/0xb0
>> [286123.157749]  xfs_file_fsync+0x3b9/0x820
>> [286123.157776]  ? lock_downgrade+0x680/0x680
>> [286123.157798]  ? xfs_filemap_pfn_mkwrite+0x10/0x10
>> [286123.157823]  ? nfsd_file_put+0x100/0x100 [nfsd]
>> [286123.157921]  nfsd_file_flush.isra.0+0x1b/0x220 [nfsd]
>> [286123.158007]  nfsd_file_put+0x79/0x100 [nfsd]
>> [286123.158088]  check_for_locks+0x152/0x200 [nfsd]
>> [286123.158191]  nfsd4_release_lockowner+0x4cf/0x850 [nfsd]
>> [286123.158393]  ? nfsd4_locku+0xd10/0xd10 [nfsd]
>> [286123.158488]  ? rcu_read_lock_bh_held+0x90/0x90
>> [286123.158525]  nfsd4_proc_compound+0xd15/0x25a0 [nfsd]
>> [286123.158699]  nfsd_dispatch+0x4ed/0xc30 [nfsd]
>> [286123.158974]  ? rcu_read_lock_bh_held+0x90/0x90
>> [286123.159010]  svc_process_common+0xd8e/0x1b20 [sunrpc]
>> [286123.159043]  ? svc_generic_rpcbind_set+0x450/0x450 [sunrpc]
>> [286123.159043]  ? nfsd_svc+0xc50/0xc50 [nfsd]
>> [286123.159043]  ? svc_sock_secure_port+0x27/0x40 [sunrpc]
>> [286123.159043]  ? svc_recv+0x1100/0x2390 [sunrpc]
>> [286123.159043]  svc_process+0x361/0x4f0 [sunrpc]
>> [286123.159043]  nfsd+0x2d6/0x570 [nfsd]
>> [286123.159043]  ? nfsd_shutdown_threads+0x2a0/0x2a0 [nfsd]
>> [286123.159043]  kthread+0x29f/0x340
>> [286123.159043]  ? kthread_complete_and_exit+0x20/0x20
>> [286123.159043]  ret_from_fork+0x22/0x30
>> [286123.159043]  </TASK>
>> [286123.187052] BUG: scheduling while atomic: nfsd/3983/0x00000002
>> [286123.187551] INFO: lockdep is turned off.
>> [286123.187918] Modules linked in: nfsd auth_rpcgss nfs_acl lockd grace sunrpc
>> [286123.188527] Preemption disabled at:
>> [286123.188535] [<0000000000000000>] 0x0
>> [286123.189255] CPU: 1 PID: 3983 Comm: nfsd Kdump: loaded Tainted: G        W         5.18.0-rc4+ #1
>> [286123.190233] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
>> [286123.190910] Call Trace:
>> [286123.190910]  <TASK>
>> [286123.190910]  dump_stack_lvl+0x57/0x7d
>> [286123.190910]  __schedule_bug.cold+0x133/0x143
>> [286123.190910]  __schedule+0x16c9/0x20a0
>> [286123.190910]  ? schedule_timeout+0x314/0x510
>> [286123.190910]  ? __sched_text_start+0x8/0x8
>> [286123.190910]  ? internal_add_timer+0xa4/0xe0
>> [286123.190910]  schedule+0xd7/0x1f0
>> [286123.190910]  schedule_timeout+0x319/0x510
>> [286123.190910]  ? rcu_read_lock_held_common+0xe/0xa0
>> [286123.190910]  ? usleep_range_state+0x150/0x150
>> [286123.190910]  ? lock_acquire+0x331/0x490
>> [286123.190910]  ? init_timer_on_stack_key+0x50/0x50
>> [286123.190910]  ? do_raw_spin_lock+0x116/0x260
>> [286123.190910]  ? rwlock_bug.part.0+0x90/0x90
>> [286123.190910]  io_schedule_timeout+0x26/0x80
>> [286123.190910]  wait_for_completion_io_timeout+0x16a/0x340
>> [286123.190910]  ? rcu_read_lock_bh_held+0x90/0x90
>> [286123.190910]  ? wait_for_completion+0x330/0x330
>> [286123.190910]  submit_bio_wait+0x135/0x1d0
>> [286123.190910]  ? submit_bio_wait_endio+0x40/0x40
>> [286123.190910]  ? xfs_iunlock+0xd5/0x300
>> [286123.190910]  ? bio_init+0x295/0x470
>> [286123.190910]  blkdev_issue_flush+0x69/0x80
>> [286123.190910]  ? blk_unregister_queue+0x1e0/0x1e0
>> [286123.190910]  ? bio_kmalloc+0x90/0x90
>> [286123.190910]  ? xfs_iunlock+0x1b4/0x300
>> [286123.190910]  xfs_file_fsync+0x354/0x820
>> [286123.190910]  ? lock_downgrade+0x680/0x680
>> [286123.190910]  ? xfs_filemap_pfn_mkwrite+0x10/0x10
>> [286123.190910]  ? nfsd_file_put+0x100/0x100 [nfsd]
>> [286123.190910]  nfsd_file_flush.isra.0+0x1b/0x220 [nfsd]
>> [286123.190910]  nfsd_file_put+0x79/0x100 [nfsd]
>> [286123.190910]  check_for_locks+0x152/0x200 [nfsd]
>> [286123.190910]  nfsd4_release_lockowner+0x4cf/0x850 [nfsd]
>> [286123.190910]  ? nfsd4_locku+0xd10/0xd10 [nfsd]
>> [286123.190910]  ? rcu_read_lock_bh_held+0x90/0x90
>> [286123.190910]  nfsd4_proc_compound+0xd15/0x25a0 [nfsd]
>> [286123.190910]  nfsd_dispatch+0x4ed/0xc30 [nfsd]
>> [286123.190910]  ? rcu_read_lock_bh_held+0x90/0x90
>> [286123.190910]  svc_process_common+0xd8e/0x1b20 [sunrpc]
>> [286123.190910]  ? svc_generic_rpcbind_set+0x450/0x450 [sunrpc]
>> [286123.190910]  ? nfsd_svc+0xc50/0xc50 [nfsd]
>> [286123.190910]  ? svc_sock_secure_port+0x27/0x40 [sunrpc]
>> [286123.190910]  ? svc_recv+0x1100/0x2390 [sunrpc]
>> [286123.190910]  svc_process+0x361/0x4f0 [sunrpc]
>> [286123.190910]  nfsd+0x2d6/0x570 [nfsd]
>> [286123.190910]  ? nfsd_shutdown_threads+0x2a0/0x2a0 [nfsd]
>> [286123.190910]  kthread+0x29f/0x340
>> [286123.190910]  ? kthread_complete_and_exit+0x20/0x20
>> [286123.190910]  ret_from_fork+0x22/0x30
>> [286123.190910]  </TASK>
>> 
>> The problem is the process tries to sleep while holding the
>> cl_lock by nfsd4_release_lockowner. I think the problem was
>> introduced with the filemap_flush in nfsd_file_put since
>> 'b6669305d35a nfsd: Reduce the number of calls to nfsd_file_gc()'.
>> The filemap_flush is later replaced by nfsd_file_flush by
>> '6b8a94332ee4f nfsd: Fix a write performance regression'.
> 
> That seems plausible, given the traces above.
> 
> But it begs the question: why was a vfs_fsync() needed by
> RELEASE_LOCKOWNER in this case? I've tried to reproduce the
> problem, and even added a might_sleep() call in nfsd_file_flush()
> but haven't been able to reproduce.

Trond, I'm assuming you switched to a synchronous flush here to
capture writeback errors. There's no other requirement for
waiting for the flush to complete, right?

To enable nfsd_file_put() to be invoked in atomic contexts again,
would the following be a reasonable short term fix:

diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
index 2c1b027774d4..96c8d07788f4 100644
--- a/fs/nfsd/filecache.c
+++ b/fs/nfsd/filecache.c
@@ -304,7 +304,7 @@ nfsd_file_put(struct nfsd_file *nf)
 {
        set_bit(NFSD_FILE_REFERENCED, &nf->nf_flags);
        if (test_bit(NFSD_FILE_HASHED, &nf->nf_flags) == 0) {
-               nfsd_file_flush(nf);
+               filemap_flush(nf->nf_file->f_mapping);
                nfsd_file_put_noref(nf);
        } else {
                nfsd_file_put_noref(nf);

--
Chuck Lever