Re: [PATCH RFC] nfsd: serialize layout stateid morphing operations

[Kinglong Mee <kinglongmee@gmail.com>]

On 11/29/2015 21:46, Jeff Layton wrote:
> On Sun, 29 Nov 2015 12:07:48 +0800
> Kinglong Mee <kinglongmee@gmail.com> wrote:
> 
>> I meet two problems with this patch,
>>
> 
> Ok, I was less sure of this patch than the other one. I think we will
> need to serialize these operations, but this may not be the best way to
> do it.
> 
> Bruce if you want to back this one for now, then I'm fine with that. It
> may be a bit before I can get to it.
> 
> 
>> 1. a dump_stack messages printed in process_one_work() at kernel/workqueue.c.
>>
>> BUG: workqueue leaked lock or atomic: kworker/u2:4/0x00000000/98#012     last function: nfsd4_run_cb_work [nfsd]
>> 1 lock held by kworker/u2:4/98:
>> #0:  (&ls->ls_mutex){......}, at: [<ffffffffa0250d34>] nfsd4_cb_layout_prepare+0x24/0x40 [nfsd]
>> CPU: 0 PID: 98 Comm: kworker/u2:4 Not tainted 4.4.0-rc2+ #333
>> Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 07/02/2015
>> Workqueue: nfsd4_callbacks nfsd4_run_cb_work [nfsd]
>> ffff8800362b9e40 000000007fe9394f ffff880036353d58 ffffffff8136dc64
>> ffff880036353dd8 ffffffff810a3f12 ffffffff810a3cbd 000000000000000a
>> ffffffffa0261d78 ffffffff82902e20 0000000000000000 ffffffffa0259241
>> Call Trace:
>> [<ffffffff8136dc64>] dump_stack+0x19/0x25
>> [<ffffffff810a3f12>] process_one_work+0x3c2/0x4c0
>> [<ffffffff810a3cbd>] ? process_one_work+0x16d/0x4c0
>> [<ffffffff810a405a>] worker_thread+0x4a/0x440
>> [<ffffffff810a4010>] ? process_one_work+0x4c0/0x4c0
>> [<ffffffff810a4010>] ? process_one_work+0x4c0/0x4c0
>> [<ffffffff810a91e5>] kthread+0xf5/0x110
>> [<ffffffff810a90f0>] ? kthread_create_on_node+0x240/0x240
>> [<ffffffff81738d0f>] ret_from_fork+0x3f/0x70
>> [<ffffffff810a90f0>] ? kthread_create_on_node+0x240/0x240
>>
> 
> 
> I guess this is just a general "hey you left a mutex locked" warning
> when finishing a workqueue job? This patch actually does want to do
> that, but I trying to tell that to lockdep may be tricky...

Yes, it's just a warning.
But, it's terrible that kernel prints it every time
when calling nfsd4_cb_layout_prepare.

> 
> 
>> 2. a mutex race between layoutrecall and layoutcommit, 
>>
>> callback thread,
>> nfsd4_cb_layout_prepare 
>>   --->mutex_lock(&ls->ls_mutex);
>>
>> layoutcommit thread,
>> nfsd4_layoutcommit
>>   ---> nfsd4_preprocess_layout_stateid
>>      --> mutex_lock(&ls->ls_mutex);   <----------------  hang 
>>
>> [  600.645142] INFO: task nfsd:11623 blocked for more than 120 seconds.
>> [  600.646337]       Not tainted 4.4.0-rc2+ #332
>> [  600.647404] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>> [  600.648546] nfsd            D ffff880064277b80     0 11623      2 0x00000000
>> [  600.649803]  ffff880064277b80 ffff880064278000 00000000ffffffff ffff88005dd241a8
>> [  600.651021]  ffffffffa025e77c 0000000000000246 ffff880064277b98 ffffffff81733103
>> [  600.652255]  ffff880063d7e100 ffff880064277ba8 ffffffff8173330e ffff880064277c28
>> [  600.653512] Call Trace:
>> [  600.654765]  [<ffffffffa025e77c>] ? nfsd4_preprocess_layout_stateid+0x37c/0x400 [nfsd]
>> [  600.656084]  [<ffffffff81733103>] schedule+0x33/0x80
>> [  600.657405]  [<ffffffff8173330e>] schedule_preempt_disabled+0xe/0x10
>> [  600.658741]  [<ffffffff817357f5>] mutex_lock_nested+0x145/0x330
>> [  600.660094]  [<ffffffffa025e77c>] ? nfsd4_preprocess_layout_stateid+0x37c/0x400 [nfsd]
>> [  600.661696]  [<ffffffffa025e77c>] nfsd4_preprocess_layout_stateid+0x37c/0x400 [nfsd]
>> [  600.663129]  [<ffffffffa025e405>] ? nfsd4_preprocess_layout_stateid+0x5/0x400 [nfsd]
>> [  600.664558]  [<ffffffff81173b8f>] ? printk+0x56/0x72
>> [  600.665990]  [<ffffffffa023e3ec>] nfsd4_layoutcommit+0x13c/0x200 [nfsd]
>> [  600.667365]  [<ffffffffa023fb98>] nfsd4_proc_compound+0x388/0x660 [nfsd]
>> [  600.668835]  [<ffffffffa022c148>] nfsd_dispatch+0xb8/0x200 [nfsd]
>> [  600.670323]  [<ffffffffa0093d89>] svc_process_common+0x409/0x650 [sunrpc]
>> [  600.671836]  [<ffffffffa0094e04>] svc_process+0xf4/0x190 [sunrpc]
>> [  600.673328]  [<ffffffffa022bb05>] nfsd+0x135/0x1a0 [nfsd]
>> [  600.674825]  [<ffffffffa022b9d5>] ? nfsd+0x5/0x1a0 [nfsd]
>> [  600.676388]  [<ffffffffa022b9d0>] ? nfsd_destroy+0xb0/0xb0 [nfsd]
>> [  600.677884]  [<ffffffff810a9175>] kthread+0xf5/0x110
>> [  600.679373]  [<ffffffff810a9080>] ? kthread_create_on_node+0x240/0x240
>> [  600.680874]  [<ffffffff81738ccf>] ret_from_fork+0x3f/0x70
>> [  600.682398]  [<ffffffff810a9080>] ? kthread_create_on_node+0x240/0x240
>> [  600.683893] 1 lock held by nfsd/11623:
>> [  600.685449]  #0:  (&ls->ls_mutex){......}, at: [<ffffffffa025e77c>] nfsd4_preprocess_layout_stateid+0x37c/0x400 [nfsd]
>> [  600.688778] Sending NMI to all CPUs:
>> [  600.690854] NMI backtrace for cpu 0
>> [  600.691909] CPU: 0 PID: 11 Comm: khungtaskd Not tainted 4.4.0-rc2+ #332
>> [  600.692523] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 07/02/2015
>> [  600.693821] task: ffff88007b900000 ti: ffff88007b8fc000 task.ti: ffff88007b8fc000
>> [  600.694496] RIP: 0010:[<ffffffff81053aca>]  [<ffffffff81053aca>] native_write_msr_safe+0xa/0x10
>> [  600.695185] RSP: 0018:ffff88007b8ffd70  EFLAGS: 00000046
>> [  600.695861] RAX: 0000000000000400 RBX: 0000000000000286 RCX: 0000000000000830
>> [  600.696539] RDX: 0000000000000000 RSI: 0000000000000400 RDI: 0000000000000830
>> [  600.697204] RBP: ffff88007b8ffd70 R08: 0000000000000400 R09: 0000000000000000
>> [  600.697862] R10: 00000000000000e4 R11: 0000000000000001 R12: ffff880063d7e100
>> [  600.698513] R13: 00000000003fff3c R14: ffff880063d7e308 R15: 0000000000000004
>> [  600.699156] FS:  0000000000000000(0000) GS:ffffffff81c27000(0000) knlGS:0000000000000000
>> [  600.699823] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> [  600.700459] CR2: 00007f366afd4000 CR3: 000000005dd56000 CR4: 00000000001406f0
>> [  600.701106] Stack:
>> [  600.701745]  ffff88007b8ffd88 ffffffff8104a860 ffffffff81047340 ffff88007b8ffd98
>> [  600.702404]  ffffffff8104a885 ffff88007b8ffda8 ffffffff8104735b ffff88007b8ffdd8
>> [  600.703058]  ffffffff813723ad 0000000000000078 ffff880063d7e100 00000000003fff3c
>> [  600.703712] Call Trace:
>> [  600.704355]  [<ffffffff8104a860>] __x2apic_send_IPI_mask.isra.2+0x60/0x70
>> [  600.705017]  [<ffffffff81047340>] ? setup_vector_irq+0x130/0x130
>> [  600.705676]  [<ffffffff8104a885>] x2apic_send_IPI_mask+0x15/0x20
>> [  600.706335]  [<ffffffff8104735b>] nmi_raise_cpu_backtrace+0x1b/0x20
>> [  600.706989]  [<ffffffff813723ad>] nmi_trigger_all_cpu_backtrace+0x14d/0x1c0
>> [  600.707693]  [<ffffffff810473b9>] arch_trigger_all_cpu_backtrace+0x19/0x20
>> [  600.708362]  [<ffffffff8112c4cf>] watchdog+0x32f/0x370
>> [  600.709031]  [<ffffffff8112c221>] ? watchdog+0x81/0x370
>> [  600.709725]  [<ffffffff8112c1a0>] ? reset_hung_task_detector+0x20/0x20
>> [  600.710398]  [<ffffffff810a9175>] kthread+0xf5/0x110
>> [  600.711067]  [<ffffffff810a9080>] ? kthread_create_on_node+0x240/0x240
>> [  600.711739]  [<ffffffff81738ccf>] ret_from_fork+0x3f/0x70
>> [  600.712405]  [<ffffffff810a9080>] ? kthread_create_on_node+0x240/0x240
>> [  600.713073] Code: 00 55 89 f9 48 89 e5 0f 32 45 31 c0 48 c1 e2 20 44 89 06 48 09 d0 5d c3 66 0f 1f 84 00 00 00 00 00 55 89 f0 89 f9 48 89 e5 0f 30 <31> c0 5d c3 66 90 55 89 f9 48 89 e5 0f 33 48 c1 e2 20 48 09 d0
>> [  600.715196] Kernel panic - not syncing: hung_task: blocked tasks
>> [  600.715889] CPU: 0 PID: 11 Comm: khungtaskd Not tainted 4.4.0-rc2+ #332
>> [  600.716540] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 07/02/2015
>> [  600.717910]  ffffffff81a4d19c 00000000480750be ffff88007b8ffd60 ffffffff8136dbf4
>> [  600.718610]  ffff88007b8ffde8 ffffffff81173559 ffff880000000008 ffff88007b8ffdf8
>> [  600.719302]  ffff88007b8ffd90 00000000480750be 0000000000000001 0000000000000001
>> [  600.719984] Call Trace:
>> [  600.720646]  [<ffffffff8136dbf4>] dump_stack+0x19/0x25
>> [  600.721330]  [<ffffffff81173559>] panic+0xd3/0x212
>> [  600.722009]  [<ffffffff8112c4db>] watchdog+0x33b/0x370
>> [  600.722686]  [<ffffffff8112c221>] ? watchdog+0x81/0x370
>> [  600.723213]  [<ffffffff8112c1a0>] ? reset_hung_task_detector+0x20/0x20
>> [  600.723674]  [<ffffffff810a9175>] kthread+0xf5/0x110
>> [  600.724107]  [<ffffffff810a9080>] ? kthread_create_on_node+0x240/0x240
>> [  600.724509]  [<ffffffff81738ccf>] ret_from_fork+0x3f/0x70
>> [  600.724903]  [<ffffffff810a9080>] ? kthread_create_on_node+0x240/0x240
>>
>> thanks,
>> Kinglong Mee
>>
> 
> This is the bigger problem, I think. The question of course is why the
> client didn't respond to the cb request? Still, holding a mutex across
> the callback RPC is pretty ugly and now that I think about it, I don't
> think it's really necessary anyway. Once we've copied the stateid, we
> aren't really changing anything else so we can let other layout ops
> proceed.
> 
> Would a patch like this fix it?

Yes, it's great.
With this patch, every thing is okay.

> 
> -----------------------8<--------------------------
> 
> [PATCH] nfsd: don't hold ls_mutex across a layout recall
> 
> We do need to serialize layout stateid morphing operations, but we
> currently hold the ls_mutex across a layout recall which is pretty
> ugly. It's also unnecessary -- once we've bumped the seqid and
> copied it, we don't need to serialize the rest of the CB_LAYOUTRECALL
> vs. anything else. Just drop the mutex once the copy is done.
> 
> Fixes: cc8a55320b5f "nfsd: serialize layout stateid morphing operations"
> Cc: stable@vger.kernel.org
> Reported-by: Kinglong Mee <kinglongmee@gmail.com>
> Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>

Tested-by: Kinglong Mee <kinglongmee@gmail.com>

thanks,
Kinglong Mee

> ---
>  fs/nfsd/nfs4layouts.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/nfsd/nfs4layouts.c b/fs/nfsd/nfs4layouts.c
> index 9ffef06b30d5..c9d6c715c0fb 100644
> --- a/fs/nfsd/nfs4layouts.c
> +++ b/fs/nfsd/nfs4layouts.c
> @@ -616,6 +616,7 @@ nfsd4_cb_layout_prepare(struct nfsd4_callback *cb)
>  
>  	mutex_lock(&ls->ls_mutex);
>  	nfs4_inc_and_copy_stateid(&ls->ls_recall_sid, &ls->ls_stid);
> +	mutex_unlock(&ls->ls_mutex);
>  }
>  
>  static int
> @@ -659,7 +660,6 @@ nfsd4_cb_layout_release(struct nfsd4_callback *cb)
>  
>  	trace_layout_recall_release(&ls->ls_stid.sc_stateid);
>  
> -	mutex_unlock(&ls->ls_mutex);
>  	nfsd4_return_all_layouts(ls, &reaplist);
>  	nfsd4_free_layouts(&reaplist);
>  	nfs4_put_stid(&ls->ls_stid);
>