Re: Oops when trying to create more than 16000 timers

Pekka Enberg
2008-12-15T21:37:50Z

Hi Ottavio,

On Mon, Dec 15, 2008 at 11:41 PM, Ottavio Campana
<ottavio.campana@dei.unipd.it> wrote:
>>> I am currently developing a software that needs approx 60k timers. I
>>> currently use timer_create and all the relative functions to manage timers.
>>>
>>> I've noticed that after having created 16039 timers I always get an oops
>>> from the kernel, which are always of the same kind:
>>>
>>> Dec 15 15:20:00 evolution kernel: [601680.417064] BUG: unable to handle
>>> kernel NULL pointer dereference at 0000000000000040 .
>>
>> This would be a kernel bug so can you please post the full oops. See
>> REPORTING-BUGS and Documentation/oops-tracing.txt for details.
>
> I hope the report is correct, please tell me if you want me to do
> something else.
>
> RIP: 0010:[<ffffffff80245291>] [<ffffffff80245291>]
> sys_timer_create+0x79/0x360
> RSP: 0018:ffff81007a5ddef8 EFLAGS: 00010286
> RAX: 0000000000000001 RBX: 0000000000000000 RCX: 0000000000000086
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000286
> RBP: 0000000000000000 R08: 0000000000000004 R09: 0000000000000001
> R10: 00007f927adb3a50 R11: 0000000000000000 R12: 00000000016ed768
> R13: 00000000016ed6d0 R14: 00007fff833dead0 R15: 00000000016ed754
> FS: 00007f927b3cd6e0(0000) GS:ffff81007d37a9c0(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> CR2: 0000000000000040 CR3: 000000007b00c000 CR4: 00000000000006e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> Process timer_tester (pid: 2743, threadinfo ffff81007a5dc000, task
> ffff81007a7936b0)
> Stack: ffff81007646f9f8 0000000000000000 0000000000000000 ffffffff8029b4ed
> 0000000000000000 ffff81007b024c80 0000000000000017 fffffffffffffff7
> 00007f927b3da000 ffffffff8029ba36 0000000000000292 0000000000000000
> Call Trace:
> [<ffffffff8029b4ed>] vfs_write+0x121/0x156
> [<ffffffff8029ba36>] sys_write+0x60/0x6e
> [<ffffffff8020beca>] system_call_after_swapgs+0x8a/0x8f
>
>
> Code: c6 0e 05 00 48 85 c0 74 3b 48 89 c5 e8 d0 a0 ff ff 48 85 c0 48 89
> 45 40 75 11 48 8b 3d e1 22 3e 00 48 89 ee 31 ed e8 fe 10 05 00 <48> 8b
> 7d 40 31 f6 ba 80 00 00 00 48 83 c7 18 e8 6b ae 0d 00 48
> RIP [<ffffffff80245291>] sys_timer_create+0x79/0x360
> RSP <ffff81007a5ddef8>
> CR2: 0000000000000040
> ---[ end trace 2e93d77cdbbd83c6 ]---
>
> Using decodecode
>
> Code: c6 0e 05 00 48 85 c0 74 3b 48 89 c5 e8 d0 a0 ff ff 48 85 c0 48 89
> 45 40 75 11 48 8b 3d e1 22 3e 00 48 89 ee 31 ed e8 fe 10 05 00 <48> 8b
> 7d 40 31 f6 ba 80 00 00 00 48 83 c7 18 e8 6b ae 0d 00 48
>
> /tmp/tmp.CcCjFxHOMN.o: file format elf64-x86-64
>
> Disassembly of section .text:
>
> 0000000000000000 <.text>:
> 0: c6 (bad)
> 1: 0e (bad)
> 2: 05 00 48 85 c0 add $0xc0854800,%eax
> 7: 74 3b je 0x44
> 9: 48 89 c5 mov %rax,%rbp
> c: e8 d0 a0 ff ff callq 0xffffffffffffa0e1
> 11: 48 85 c0 test %rax,%rax
> 14: 48 89 45 40 mov %rax,0x40(%rbp)
> 18: 75 11 jne 0x2b
> 1a: 48 8b 3d e1 22 3e 00 mov 0x3e22e1(%rip),%rdi # 0x3e2302
> 21: 48 89 ee mov %rbp,%rsi
> 24: 31 ed xor %ebp,%ebp
> 26: e8 fe 10 05 00 callq 0x51129
>
> /tmp/tmp.CcCjFxHOMN.o: file format elf64-x86-64
>
> Disassembly of section .text:
>
> 0000000000000000 <.text>:
> 0: 48 8b 7d 40 mov 0x40(%rbp),%rdi
> 4: 31 f6 xor %esi,%esi
> 6: ba 80 00 00 00 mov $0x80,%edx
> b: 48 83 c7 18 add $0x18,%rdi
> f: e8 6b ae 0d 00 callq 0xdae7f
> 14: 48 rex.W

I think you're simply hitting RLIMIT_SIGPENDING and then tripping over
a bug in alloc_posix_timer() that's fixed by commit
aa94fbd5ccd840c8ab26d02439ec799b03a72547 ("fix error-path NULL deref
in alloc_posix_timer()") in 2.6.28-rc8.

Dan, can you please send your patch to the -stable queue as well?

Pekka