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    SubjectRe: Oops when trying to create more than 16000 timers
    On Mon, Dec 15, 2008 at 11:37:38PM +0200, Pekka Enberg wrote:
    > 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?
    >

    This patch is already in the 2.6.27 release.

    thanks,

    greg k-h


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