linux-kernel - RE: [RFC] sunrpc: Fix race between work-queue and rpc_killall

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Date:	Tue, 12 Jul 2011 10:25:02 -0700
From:	"Myklebust, Trond" <Trond.Myklebust@...app.com>
To:	"Ben Greear" <greearb@...delatech.com>
Cc:	<linux-nfs@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: RE: [RFC] sunrpc:  Fix race between work-queue and rpc_killall_tasks.

> -----Original Message-----
> From: Ben Greear [mailto:greearb@...delatech.com]
> Sent: Tuesday, July 12, 2011 1:15 PM
> To: Myklebust, Trond
> Cc: linux-nfs@...r.kernel.org; linux-kernel@...r.kernel.org
> Subject: Re: [RFC] sunrpc: Fix race between work-queue and
> rpc_killall_tasks.
> 
> On 07/08/2011 03:14 PM, Myklebust, Trond wrote:
> 
> >>    [<ffffffff81105907>] print_trailer+0x131/0x13a
> >>    [<ffffffff81105945>] object_err+0x35/0x3e
> >>    [<ffffffff811077b3>] verify_mem_not_deleted+0x7a/0xb7
> >>    [<ffffffffa02891e5>] rpcb_getport_done+0x23/0x126 [sunrpc]
> >>    [<ffffffffa02810df>] rpc_exit_task+0x3f/0x6d [sunrpc]
> >>    [<ffffffffa02814d8>] __rpc_execute+0x80/0x253 [sunrpc]
> >>    [<ffffffffa02816ed>] ? rpc_execute+0x42/0x42 [sunrpc]
> >>    [<ffffffffa02816fd>] rpc_async_schedule+0x10/0x12 [sunrpc]
> >>    [<ffffffff81061343>] process_one_work+0x230/0x41d
> >>    [<ffffffff8106128e>] ? process_one_work+0x17b/0x41d
> >>    [<ffffffff8106379f>] worker_thread+0x133/0x217
> >>    [<ffffffff8106366c>] ? manage_workers+0x191/0x191
> >>    [<ffffffff81066f9c>] kthread+0x7d/0x85
> >>    [<ffffffff81485ee4>] kernel_thread_helper+0x4/0x10
> >>    [<ffffffff8147f0d8>] ? retint_restore_args+0x13/0x13
> >>    [<ffffffff81066f1f>] ? __init_kthread_worker+0x56/0x56
> >>    [<ffffffff81485ee0>] ? gs_change+0x13/0x13
> >
> > The calldata gets freed in the rpc_final_put_task() which shouldn't
> ever be run while the task is still referenced in __rpc_execute
> >
> > IOW: it should be impossible to call rpc_exit_task() after
> rpc_final_put_task
> 
> I added lots of locking around the calldata, work-queue logic, and
> such, and
> still the problem persists w/out hitting any of the debug warnings or
> poisoned
> values I put in.  It almost seems like tk_calldata is just assigned to
> two
> different tasks.
> 
> While poking through the code, I noticed that 'map' is static in
> rpcb_getport_async.
> 
> That would seem to cause problems if two threads called this method at
> the same time, possibly causing tk_calldata to be assigned to two
> different
> tasks???
> 
> Any idea why it is static?

Doh! That is clearly a typo dating all the way back to when Chuck wrote that function.

Yes, that would definitely explain your problem.

Cheers
  Trond