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SubjectRe: Ugly rmap NULL ptr deref oopsie on hibernate (was Linux 2.6.34-rc3)


On Tue, 6 Apr 2010, Borislav Petkov wrote:
>
> [ 2995.478125] PM: Preallocating image memory...
> [ 2995.713692] BUG: unable to handle kernel NULL pointer dereference at (null)
> [ 2995.714001] IP: [<ffffffff810c194d>] page_referenced+0xee/0x1dc
> [ 2995.714001] PGD 22d1b8067 PUD 22dd85067 PMD 0
> [ 2995.714001] Oops: 0000 [#1] PREEMPT SMP
> [ 2995.714001] last sysfs file: /sys/power/state
> [ 2995.714001] CPU 0
> [ 2995.714001] Modules linked in: tun powernow_k8 cpufreq_ondemand cpufreq_powersave cpufreq_userspace freq_table cpufreq_conservative binfmt_misc kvm_amd kvm ipv6 vfat fat dm_crypt dm_mod ohci_hcd pcspkr 8250_pnp 8250 k10temp edac_core serial_core
> [ 2995.714001]
> [ 2995.714001] Pid: 7440, comm: hib.sh Not tainted 2.6.34-rc3-00288-gab195c5 #1 M3A78 PRO/System Product Name
> [ 2995.714001] RIP: 0010:[<ffffffff810c194d>] [<ffffffff810c194d>] page_referenced+0xee/0x1dc
> [ 2995.714001] RSP: 0018:ffff88022fa038b8 EFLAGS: 00010283
> [ 2995.714001] RAX: ffff88022d747098 RBX: ffffea00078efb70 RCX: 0000000000000000
> [ 2995.714001] RDX: ffff88022fa03cf8 RSI: ffff88022d747070 RDI: ffff88022fb32520
> [ 2995.714001] RBP: ffff88022fa03938 R08: 0000000000000002 R09: 0000000000000000
> [ 2995.714001] R10: ffff88022fa038a8 R11: ffff88022d295d10 R12: 0000000000000000
> [ 2995.714001] R13: ffffffffffffffe0 R14: ffff88022d747058 R15: ffff88022fa03a00
> [ 2995.714001] FS: 00007f4da8b966f0(0000) GS:ffff88000a000000(0000) knlGS:0000000000000000
> [ 2995.714001] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> [ 2995.714001] CR2: 0000000000000000 CR3: 000000022d11e000 CR4: 00000000000006f0
> [ 2995.714001] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [ 2995.714001] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> [ 2995.714001] Process hib.sh (pid: 7440, threadinfo ffff88022fa02000, task ffff88022fb32520)
> [ 2995.714001] Stack:
> [ 2995.714001] ffff88022d747098 00000000813fd2ac ffffffff8165ee28 0000000000000416
> [ 2995.714001] <0> ffff88022fa038f8 ffffffff810c6d40 ffffea00078fae60 ffffea00078fae60
> [ 2995.714001] <0> ffff88022fa03938 00000002810abd98 ffffea00078ec530 ffffea00078efb98
> [ 2995.714001] Call Trace:
> [ 2995.714001] [<ffffffff810c6d40>] ? swapcache_free+0x37/0x3c
> [ 2995.714001] [<ffffffff810ac31d>] shrink_page_list+0x171/0x4b1
> [ 2995.714001] [<ffffffff813fd1e6>] ? _raw_spin_unlock_irq+0x30/0x58
> [ 2995.714001] [<ffffffff810ac9b9>] shrink_inactive_list+0x35c/0x623
> [ 2995.714001] [<ffffffff810acd94>] ? shrink_zone+0x114/0x3d4
> [ 2995.714001] [<ffffffff81064f29>] ? print_lock_contention_bug+0x1b/0xe1
> [ 2995.714001] [<ffffffff813fc790>] ? _raw_spin_lock_irq+0x19/0x79
> [ 2995.714001] [<ffffffff810acf8a>] shrink_zone+0x30a/0x3d4
> [ 2995.714001] [<ffffffff810ad19e>] ? shrink_slab+0x14a/0x15c
> [ 2995.714001] [<ffffffff810adb65>] do_try_to_free_pages+0x176/0x27f
> [ 2995.714001] [<ffffffff8103de67>] ? irq_exit+0x93/0x95
> [ 2995.714001] [<ffffffff810add03>] shrink_all_memory+0x95/0xc4
> [ 2995.714001] [<ffffffff810ab0f0>] ? isolate_pages_global+0x0/0x217
> [ 2995.714001] [<ffffffff81077503>] ? count_data_pages+0x65/0x79
> [ 2995.714001] [<ffffffff8107776a>] hibernate_preallocate_memory+0x1aa/0x2cb
> [ 2995.714001] [<ffffffff813f95b5>] ? printk+0x41/0x44
> [ 2995.714001] [<ffffffff810760b3>] hibernation_snapshot+0x36/0x1e1
> [ 2995.714001] [<ffffffff8107632c>] hibernate+0xce/0x172
> [ 2995.714001] [<ffffffff81075099>] state_store+0x5c/0xd3
> [ 2995.714001] [<ffffffff8118728f>] kobj_attr_store+0x17/0x19
> [ 2995.714001] [<ffffffff81127b69>] sysfs_write_file+0x108/0x144
> [ 2995.714001] [<ffffffff810d66ff>] vfs_write+0xb2/0x153
> [ 2995.714001] [<ffffffff810641a9>] ? trace_hardirqs_on_caller+0x1f/0x14b
> [ 2995.714001] [<ffffffff810d6863>] sys_write+0x4a/0x71
> [ 2995.714001] [<ffffffff810021db>] system_call_fastpath+0x16/0x1b
> [ 2995.714001] Code: 3b 56 10 73 1e 48 83 fa f2 74 18 48 8d 4d cc 4d 89 f8 48 89 df e8 4d f2 ff ff 41 01 c4 83 7d cc 00 74 19 4d 8b 6d 20 49 83 ed 20 <49> 8b 45 20 0f 18 08 49 8d 45 20 48 39 45 80 75 aa 4c 89 f7 e8
> [ 2995.714001] RIP [<ffffffff810c194d>] page_referenced+0xee/0x1dc
> [ 2995.714001] RSP <ffff88022fa038b8>
> [ 2995.714001] CR2: 0000000000000000
> [ 2995.729717] ---[ end trace 92c25d74e4800968 ]---

So again, I can show that the code has never actually been through the
loop. The above code decodes to:

0: 3b 56 10 cmp 0x10(%rsi),%edx
3: 73 1e jae 0x23
5: 48 83 fa f2 cmp $0xfffffffffffffff2,%rdx
9: 74 18 je 0x23
b: 48 8d 4d cc lea -0x34(%rbp),%rcx
f: 4d 89 f8 mov %r15,%r8
12: 48 89 df mov %rbx,%rdi
15: e8 4d f2 ff ff callq 0xfffffffffffff267
1a: 41 01 c4 add %eax,%r12d
1d: 83 7d cc 00 cmpl $0x0,-0x34(%rbp)
21: 74 19 je 0x3c
23: 4d 8b 6d 20 mov 0x20(%r13),%r13
27: 49 83 ed 20 sub $0x20,%r13
2b:* 49 8b 45 20 mov 0x20(%r13),%rax <-- trapping instruction
2f: 0f 18 08 prefetcht0 (%rax)
32: 49 8d 45 20 lea 0x20(%r13),%rax
36: 48 39 45 80 cmp %rax,-0x80(%rbp)
3a: 75 aa jne 0xffffffffffffffe6
3c: 4c 89 f7 mov %r14,%rdi
3f: e8 .byte 0xe8
and in your case, if we had gone through the loop, then %rax would still
contain the return value from page_referenced_one().

But %rax is a kernel pointer, and %r12d is 0.

So again, it's actually anon_vma.head.next that is NULL, not any of the
entries on the list itself.

Now, I can see several cases for this:

- the obvious one: anon_vma just wasn't correctly initialized, and is
missing a INIT_LIST_HEAD(&anon_vma->head). That's either a slab bug (we
don't have a whole lot of coverage of constructors), or somebody
allocated an anon_vma without using the anon_vma_cachep.

- Related to the above: perhaps the RCU freeing isn't working, or
slub/slab/slob ends up reusing the allocations for something else than
anonvma's, so together with the race _and_ an unlucky re-use, you get
some odd crud.

I haven't looked at the kernel config files: do they perhaps share the
same (odd?) SLUB/SLAB/SLOB config?

- anon_vma isn't actually an anonvma at all. 'page->mapping' was crud
with the low bit set. That sounds unlikely, but who knows. The ksm code
sets mapping to "stable_node + PAGE_MAPPING_ANON | PAGE_MAPPING_KSM"
Did people have KSM enabled?

.. and probably other things I haven't even thought about.

Linus


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