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Message-ID: <m18xg1akmd.fsf@ebiederm.dsl.xmission.com>
Date: Wed, 17 Jan 2007 05:44:10 -0700
From: ebiederm@...ssion.com (Eric W. Biederman)
To: "Daniel Hokka Zakrisson" <daniel@...ac.com>
Cc: linux-kernel@...r.kernel.org, herbert@...hfloor.at, akpm@...l.org,
trond.myklebust@....uio.no,
Linux Containers <containers@...ts.osdl.org>,
Oleg Nesterov <oleg@...sign.ru>
Subject: Re: NFS causing oops when freeing namespace
"Daniel Hokka Zakrisson" <daniel@...ac.com> writes:
> The test-case at the bottom causes the following recursive Oopsing on
> 2.6.20-rc5:
A few more people added to the CC who might have a clue.
>
> BUG: unable to handle kernel NULL pointer dereference at virtual address
> 00000504
> printing eip:
> c02292d4
> *pde = 00000000
> Oops: 0002 [#1]
> PREEMPT SMP
> Modules linked in:
> CPU: 0
> EIP: 0060:[<c02292d4>] Not tainted VLI
> EFLAGS: 00010046 (2.6.20-rc5 #11)
> EIP is at _raw_spin_trylock+0x4/0x30
> eax: 00000000 ebx: 00000213 ecx: 00000001 edx: 00000504
> esi: 00000504 edi: c1493da0 ebp: d5b5ff3c esp: d5b5fee0
> ds: 007b es: 007b ss: 0068
> Process mount (pid: 2618, ti=d5b5e000 task=c17fdaa0 task.ti=d5b5e000)
> Stack: c03be6f0 00000000 00000000 c01f6115 c04240dc c17fdaa0 c17fdc2c
> 00000000
> 00000000 d555ebe0 c04734a0 c01d26bd c01d8e9c d553b800 c0161c5d
> d707443c
> d54cedc0 c0175e0e d779c9a0 d779cd60 c1493f20 d7f1caa0 c0175e86
> d54cee40
> 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
> =======================
> Code: ff ff c3 8d 74 26 00 c7 00 00 00 00 01 c7 40 08 ed 1e af de c7 40 10
> ff ff ff ff c7 40 0c ff ff ff ff c3 8d 74 26 00 89 c2 31 c0 <86> 02 31 c9
> 84 c0 0f 9f c1 85 c9 74 12 65 a1 04 00 00 00 89 42
> EIP: [<c02292d4>] _raw_spin_trylock+0x4/0x30 SS:ESP 0068:d5b5fee0
> <1>BUG: unable to handle kernel NULL pointer dereference at virtual
> address 00000024
> printing eip:
> c011e8dd
> *pde = 00000000
> Oops: 0000 [#2]
> PREEMPT SMP
> Modules linked in:
> CPU: 0
> EIP: 0060:[<c011e8dd>] Not tainted VLI
> EFLAGS: 00010006 (2.6.20-rc5 #11)
> EIP is at do_exit+0x4d/0x810
> eax: 00000000 ebx: d5b5fea8 ecx: c17fdaa0 edx: 00000001
> esi: c17fdaa0 edi: 00000a3a ebp: 0000000b esp: d5b5fde4
> ds: 007b es: 007b ss: 0068
> Process mount (pid: 2618, ti=d5b5e000 task=c17fdaa0 task.ti=d5b5e000)
> Stack: 00000a3a d5b5e000 c17fdaa0 d5b5e000 00000003 c046a307 0000000f
> d5b5fee0
> 00000068 00000013 c011c3cb c042b321 d5b5fe24 d5b5fea8 d5b5fee0
> 00000068
> 00000000 c0104816 c041347f 00000068 d5b5fee0 00000001 d5b5fea8
> c0414df5
> Call Trace:
> [<c011c3cb>] printk+0x1b/0x20
> [<c0104816>] die+0x246/0x260
> [<c03c09b0>] do_page_fault+0x2e0/0x630
> [<c011c2cf>] vprintk+0x28f/0x370
> [<c03c06d0>] do_page_fault+0x0/0x630
> [<c03beea4>] error_code+0x7c/0x84
> [<c03b007b>] rpc_wake_up+0x4b/0x70
> [<c02292d4>] _raw_spin_trylock+0x4/0x30
> [<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
> =======================
> Code: 03 00 00 89 e0 25 00 e0 ff ff f7 40 14 00 ff ff 0f 0f 85 69 03 00 00
> 8b be a4 00 00 00 85 ff 0f 84 43 03 00 00 8b 86 48 04 00 00 <8b> 50 24 3b
> 72 10 0f 84 1c 03 00 00 65 a1 08 00 00 00 f6 40 11
> EIP: [<c011e8dd>] do_exit+0x4d/0x810 SS:ESP 0068:d5b5fde4
>
> It seems to go on forever. addr2line output follows:
> $ addr2line -e vmlinux c02292d4 c03be6f0 c01f6115 c01d26bd c01d8e9c
> c0161c5d c0175e0e c0175e86 c0132b3e c011f021 c011e8dd
> include/asm/spinlock.h:90
> kernel/spinlock.c:280
> fs/lockd/svc.c:345
> fs/nfs/client.c:782
> fs/nfs/super.c:679
> fs/super.c:184
> include/linux/list.h:299
> fs/namespace.c:1879
> include/linux/mnt_namespace.h:26
> include/linux/nsproxy.h:42
> include/linux/pid_namespace.h:42
>
> The problem appears to be that fs/lockd/svc.c:lockd_down tries to lock
> current->sighand->siglock, but during the time it's sleeping the process
> is reaped and released, setting sighand to NULL.
>
> This also affects 2.6.19.2, but since there are no pid spaces there, it's
> "just" a single oops, and doesn't make the machine totally unusable.
Ugh. This is why I have been deliberately trying to finish the kernel_thread
to kthread conversion before I finished the pid namespace. It looks
like whatever part of the pid namespace made it into nsproxy for
2.6.20-rcX may need to come out if it is causing problems, but
since it is always shared that doesn't seem right.
I find it weird that you are describing current as having exited,
while it is sleeping.
sighand in the task_struct is non-null is good until release_task is
called.
I don't think we are reapable at the point so sighand going NULL
shouldn't cause problems.
Thanks for the test-case. If it is as easy to reproduce as this looks
we should be able to track this down fairly quickly.
> Test-case, execute as ./a.out mount -t nfs ...:
> #include <stdio.h>
> #include <sched.h>
> #include <unistd.h>
>
> int main(int argc, char *argv[])
> {
> if (unshare(CLONE_NEWNS) == -1) {
> perror("unshare");
> exit(1);
> }
> execv("/bin/mount", argv+1);
> perror("execv(mount)");
> return 1;
> }
>
Now back to bed with me.
Eric
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