linux-kernel - Re: NFS causing oops when freeing namespace

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Date:	Wed, 17 Jan 2007 20:20:37 +0100
From:	Cedric Le Goater <clg@...ibm.com>
To:	Oleg Nesterov <oleg@...sign.ru>
CC:	Daniel Hokka Zakrisson <daniel@...ac.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	linux-kernel@...r.kernel.org, herbert@...hfloor.at, akpm@...l.org,
	trond.myklebust@....uio.no,
	Linux Containers <containers@...ts.osdl.org>
Subject: Re: NFS causing oops when freeing namespace

Oleg Nesterov wrote:
> On 01/17, Daniel Hokka Zakrisson wrote:
>>>> Call Trace:
>>>>  [<c03be6f0>] _spin_lock_irqsave+0x20/0x90
>>>>  [<c01f6115>] lockd_down+0x125/0x190
>>>>  [<c01d26bd>] nfs_free_server+0x6d/0xd0
>>>>  [<c01d8e9c>] nfs_kill_super+0xc/0x20
>>>>  [<c0161c5d>] deactivate_super+0x7d/0xa0
>>>>  [<c0175e0e>] release_mounts+0x6e/0x80
>>>>  [<c0175e86>] __put_mnt_ns+0x66/0x80
>>>>  [<c0132b3e>] free_nsproxy+0x5e/0x60
>>>>  [<c011f021>] do_exit+0x791/0x810
>>>>  [<c011f0c6>] do_group_exit+0x26/0x70
>>>>  [<c0103142>] sysenter_past_esp+0x5f/0x85
>>>>  [<c03b0033>] rpc_wake_up+0x3/0x70
>> It was the only semi-plausible explanation I could come up with. I added a
>> printk in do_exit right before exit_task_namespaces, where sighand was
>> still set, and one right before the spin_lock_irq in lockd_down, where it
>> had suddenly been set to NULL.
> 
> I can't reproduce the problem, but

I did on a 2.6.20-rc4-mm1.

> 	do_exit:
> 		exit_notify(tsk);
> 		exit_task_namespaces(tsk);
> 
> the task could be reaped by its parent in between.

indeed. while it goes spleeping in lockd_down() just before it does

	spin_lock_irq(&current->sighand->siglock);

current->sighand is valid before interruptible_sleep_on_timeout() and
not after.
 
> We should not use ->signal/->sighand after exit_notify().
> 
> Can we move exit_task_namespaces() up?

yes but I moved it down because it invalidates ->nsproxy ... 

C.

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