linux-kernel - Re: [Problem] kernel hangs at boot (bisected 892d208bcf)

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Date:	Thu, 19 Jan 2012 11:01:21 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Dirk Gouders <gouders@...bocholt.fh-gelsenkirchen.de>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [Problem] kernel hangs at boot (bisected 892d208bcf)

Hi Dirk,

On Wed, Jan 18, 2012 at 07:32:59PM +0000, Dirk Gouders wrote:
> I am not sure if you are the correct person to contact,

I am for kmemleak :) but I'm not sure it's kmemleak's fault here.

> but
> I noticed a regression in Linus' master branch and bisected this to
> commit 892d208bcf
> "Merge tag 'kmemleak' of git://git.kernel.org/pub/scm/linux/kernel/git/cmarinas/linux".
...
> Freeing unused kernel memory: 608k freed
> kernel tried to execute NX-protected page - exploit attempt? (uid: 0)
> BUG: unable to handle kernel paging request at ffffffff818b232b
> IP: [<ffffffff818b232b>] kmemleak_late_init+0x8a/0x8a
> PGD 17ed067 PUD 17f1063 PMD 3c6a9063 PTE 80000000018b2163
> Oops: 0011 [#1] SMP
> CPU 1
> Modules linked in:
> 
> Pid: 1, comm: swapper/0 Not tainted 3.2.0-09104-gccb19d2 #4 Bochs Bochs
> RIP: 0010:[<ffffffff818b232b>]  [<ffffffff818b232b>] kmemleak_late_init+0x8a/0x8a
> RSP: 0018:ffff88003fd03e58  EFLAGS: 00010282
> RAX: 0000000000000001 RBX: ffff88003dbd2600 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: ffff88003dbd2600 RDI: 0000000000000002
> RBP: ffff88003e015488 R08: ffff88003fd0d5c0 R09: ffff88003fd122e0
> R10: 0000000000000400 R11: ffffffff81572da5 R12: ffffea0000f6f480
> R13: ffffffff810aa687 R14: 0000000000000000 R15: ffff88003e31dbc8
> FS:  0000000000000000(0000) GS:ffff88003fd00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> CR2: ffffffff818b232b CR3: 00000000017eb000 CR4: 00000000000006e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> Process swapper/0 (pid: 1, threadinfo ffff88003e272000, task ffff88003e278000)
> Stack:
>  ffffffff810fed11 ffff88003dbd2680 ffff88003fd0d830 ffffffff81805980
>  ffff88003d48dd00 ffff88003fd0d860 ffffffff810aa687 ffff88003e2ad420
>  0000000a3e2ad820 ffff88003e272000 ffff88003e278000 ffff88003fd03eb0
> Call Trace:
>  <IRQ>
>  [<ffffffff810fed11>] ? kmem_cache_free+0x4f/0xd9
>  [<ffffffff810aa687>] ? __rcu_process_callbacks+0x1bf/0x2e2
>  [<ffffffff810aa7f4>] ? rcu_process_callbacks+0x4a/0x95
> [<ffffffff8105cc1a>] ? __do_softirq+0xb6/0x171
>  [<ffffffff8155a58c>] ? call_softirq+0x1c/0x30
>  [<ffffffff81032d85>] ? do_softirq+0x31/0x68
>  [<ffffffff8105ce7f>] ? irq_exit+0x44/0x9e
>  [<ffffffff81047fd9>] ? smp_apic_timer_interrupt+0x85/0x95
>  [<ffffffff818d1000>] ? free_area_init_node+0x21f/0x2fb
>  [<ffffffff81559c4b>] ? apic_timer_interrupt+0x6b/0x70
>  <EOI>
>  [<ffffffff818d1000>] ? free_area_init_node+0x21f/0x2fb
>  [<ffffffff818d14b0>] ? __next_free_mem_range_rev+0x57/0x11e
>  [<ffffffff8104d31b>] ? free_init_pages+0xea/0x110
>  [<ffffffff810001c0>] ? init_post+0xe/0xbb
>  [<ffffffff81895b93>] ? kernel_init+0x10f/0x113
>  [<ffffffff8155a494>] ? kernel_thread_helper+0x4/0x10
>  [<ffffffff81895a84>] ? start_kernel+0x319/0x319
>  [<ffffffff8155a490>] ? gs_change+0xb/0xb
> Code: cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc <cc> cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc
> RIP  [<ffffffff818b232b>] kmemleak_late_init+0x8a/0x8a
>  RSP <ffff88003fd03e58>
> CR2: ffffffff818b232b

I don't really see how kmemleak could cause such error (or any of the
recent changes I have made). It looks like some of the code in the
.init.text section is not executable.

If you still have the vmlinux around, could you please run:

addr2line -i -f -e vmlinux ffffffff818b232b

The code shown shown in the oops message is also a bit weird (all 0xcc).
Maybe you could do an objdump -d in that area, see if it looks like sane
asm code.

Thanks.

-- 
Catalin
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