Re: namespaces?: bug at mm/slub.c:2750

Andrew Morton
2009-02-11T08:08:28Z

(cc's added)

On Wed, 11 Feb 2009 08:55:08 +0100 Vegard Nossum <vegard.nossum@gmail.com> wrote:

> On Sat, Feb 7, 2009 at 1:15 AM, Andrew Morton <akpm@linux-foundation.org> wrote:
> > On Fri, 6 Feb 2009 12:35:56 +0100
> > Eric Sesterhenn <snakebyte@gmx.de> wrote:
> >>
> >> with todays -git i get the following bug when i reboot the machine
> >>
> >> [ 94.369135] ------------[ cut here ]------------
> >> [ 94.369344] kernel BUG at mm/slub.c:2750!
>
> [...]
>
> > Well that's ugly. We seem to have passed a non-slab address into
> > kfree().
> >
> > void kfree(const void *x)
> > {
> > struct page *page;
> > void *object = (void *)x;
> >
> > if (unlikely(ZERO_OR_NULL_PTR(x)))
> > return;
> >
> > page = virt_to_head_page(x);
> > if (unlikely(!PageSlab(page))) {
> > BUG_ON(!PageCompound(page));
> >
> >
> > doing BUG_ON(!PageCompound) is a rather odd way of reporting that.
> >
>
> This might be pointing out the obvious, but page allocator
> pass-through means that we can't really tell slab pages from page
> allocator pages. But since pass-through uses GFP_COMP, we know it'd be
> a bug to pass a non-compound page into this function.
>
> > I'm unsure what could have caused this. Could you have a play around
> > please? Set all the memory debug options, try using slab instead of
> > slub, etc?
>
> I think it is trying to free the init_user_ns (because of a
> refcounting bug). I am able to reproduce it with a clean stack trace:
>
> [ 648.864710] ------------[ cut here ]------------
> [ 648.865554] kernel BUG at mm/slub.c:2750!
> [ 648.865554] invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC
> [ 648.865554] last sysfs file: /sys/devices/pnp0/00:0d/id
> [ 648.865554] CPU 1
> [ 648.865554] Modules linked in:
> [ 648.865554] Pid: 917, comm: udevd Not tainted 2.6.29-rc3 #223
> [ 648.865554] RIP: 0010:[<ffffffff810b99c9>] [<ffffffff810b99c9>]
> kfree+0x29/0x87
> [ 648.865554] RSP: 0018:ffff88003f187e28 EFLAGS: 00010246
> [ 648.865554] RAX: 0100000000000400 RBX: ffffffff8171fe00 RCX: 0000000000000086
> [ 648.865554] RDX: ffffe20000050ec8 RSI: 0000000000000085 RDI: ffffe20000050ec8
> [ 648.865554] RBP: ffff88003f187e38 R08: 0000000000000000 R09: ffffffff81819cb0
> [ 648.865554] R10: 0000000000000002 R11: ffff88003f187e98 R12: ffffffff81072144
> [ 648.865554] R13: 00000000000000cf R14: ffffffff818b13e0 R15: 000000000000000a
> [ 648.865554] FS: 0000000000000000(0000) GS:ffff88003f156f80(0063)
> knlGS:00000000f7fac700
> [ 648.865554] CS: 0010 DS: 002b ES: 002b CR0: 000000008005003b
> [ 648.865554] CR2: 0000000009b2d630 CR3: 000000003e92c000 CR4: 00000000000006a0
> [ 648.865554] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [ 648.865554] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> [ 648.865554] Process udevd (pid: 917, threadinfo ffff88003e458000,
> task ffff88003f1b8e80)
> [ 648.865554] Stack:
> [ 648.865554] ffffffff8171fe00 ffffffff81072144 ffff88003f187e58
> ffffffff81072169
> [ 648.865554] ffffffff818b13e0 ffffffff8171fe00 ffff88003f187e78
> ffffffff811b2f68
> [ 648.865554] ffff88003dd4c500 0000000000000286 ffff88003f187e98
> ffffffff81046712
> [ 648.865554] Call Trace:
> [ 648.865554] <IRQ> <0> [<ffffffff81072144>] ? free_user_ns+0x0/0x29
> [ 648.865554] [<ffffffff81072169>] free_user_ns+0x25/0x29
> [ 648.865554] [<ffffffff811b2f68>] kref_put+0x66/0x72
> [ 648.865554] [<ffffffff81046712>] free_uid+0x4f/0x90
> [ 648.865554] [<ffffffff810555b8>] put_cred_rcu+0xa5/0xb9
> [ 648.865554] [<ffffffff8107ea86>] __rcu_process_callbacks+0x1f4/0x263
> [ 648.865554] [<ffffffff8107eb2c>] rcu_process_callbacks+0x37/0x5d
> [ 648.865554] [<ffffffff81041bd3>] __do_softirq+0x88/0x149
> [ 648.865554] [<ffffffff8100d53c>] call_softirq+0x1c/0x28
> [ 648.865554] [<ffffffff8100e4e9>] do_softirq+0x39/0x7b
> [ 648.865554] [<ffffffff81041946>] irq_exit+0x44/0x7e
> [ 648.865554] [<ffffffff814c3d8f>] smp_apic_timer_interrupt+0x98/0xb1
> [ 648.865554] [<ffffffff8100cf73>] apic_timer_interrupt+0x13/0x20
> [ 648.865554] <EOI> <0>Code: c9 c3 55 48 89 e5 41 54 53 0f 1f 44 00
> 00 48 83 ff 10 48 89 fb 7
> 6 6d e8 1d ed ff ff 48 89 c7 48 8b 00 84 c0 78 10 f6 c4 60 75 04 <0f>
> 0b eb fe e8 f4 cd fd ff e
> b 4e 48 8b 4d 08 4c 8b 4f 10 9c 41
> [ 648.865554] RIP [<ffffffff810b99c9>] kfree+0x29/0x87
> [ 648.865554] RSP <ffff88003f187e28>
> [ 649.131912] ---[ end trace a48f49f69d2bcb3e ]---
> [ 649.136840] Kernel panic - not syncing: Fatal exception in interrupt
> [ 649.143558] Rebooting in 10 seconds..
>
> And if you look closely in the stack dump, you will find init_user_ns:
>
> ffffffff8171fe00 D init_user_ns
>
> In case you missed it, KOSAKI Motohiro posted a similar stack-trace
> (but not the same BUG) in this thread:
> http://lkml.org/lkml/2009/2/10/7
>

Both traces include the newly-added put_cred_rcu(). Suspicious.