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    SubjectRe: 2.6.30-rc kills my box hard - and lockdep chains
    On Thu, 14 May 2009 09:49:51 -0600 Jonathan Corbet <> wrote:

    > So...every now and then I return to my system (a dual-core 64-bit
    > x86 box) only to find it totally dead. Lights are on but there's no
    > disk activity, no ping responses, no alternative to simply pulling the
    > plug. It happens fairly reliably about once a day with the 2.6.30-rc
    > kernels; it does not happen with 2.6.29.
    > I'm at a bit of a loss for how to try to track this one down. "System
    > disappears without a trace" isn't much to go on. I can't reproduce it
    > at will; even the "maintain an unsaved editor buffer with hours' worth
    > of work" trick doesn't seem to work this time.
    > One clue might be found here, perhaps: I didn't have lockdep enabled but I do
    > now.

    So the lockup isn't due to lockdep.

    Did you try all the usual sysrq-P, nmi-watchdog stuff?

    Is netconsole enabled, to see if it squawked as it died?

    > May 14 01:06:55 bike kernel: [38730.804833] BUG: MAX_LOCKDEP_CHAINS too low!
    > May 14 01:06:55 bike kernel: [38730.804838] turning off the locking correctness validator.
    > May 14 01:06:55 bike kernel: [38730.804843] Pid: 5321, comm: tar Tainted: G W 2.6.30-rc5 #11
    > May 14 01:06:55 bike kernel: [38730.804846] Call Trace:
    > May 14 01:06:55 bike kernel: [38730.804854] [<ffffffff8025df59>] __lock_acquire+0x57f/0xbc9
    > May 14 01:06:55 bike kernel: [38730.804860] [<ffffffff8020f3a9>] ? print_context_stack+0xfa/0x119
    > May 14 01:06:55 bike kernel: [38730.804866] [<ffffffff80394da9>] ? get_hash_bucket+0x28/0x34
    > ...
    > May 14 01:06:55 bike kernel: [38730.805340] [<ffffffff802c2741>] ? filldir+0x0/0xc4
    > May 14 01:06:55 bike kernel: [38730.805344] [<ffffffff802c293d>] vfs_readdir+0x79/0xb6
    > May 14 01:06:55 bike kernel: [38730.805348] [<ffffffff802c2ac3>] sys_getdents+0x81/0xd1
    > May 14 01:06:55 bike kernel: [38730.805353] [<ffffffff8020bcdb>] system_call_fastpath+0x16/0x1b
    > That's quite the call stack... and, evidently, a lot of lock chains...

    It is a deep stack trace.

    And unfortunately

    a) that diagnostic didn't print the stack pointer value, from which
    we can often work out if we're looking at a stack overflow.

    b) I regularly think it would be useful if that stack backtrace were
    to print out the actual stack address, so we could see how much
    stack each function is using.

    I just went in to hack these things up, but the x86 stacktrace
    code which I used to understand has become stupidly complex so I
    gave up.

    What tools do we have to diagnose a possible kernel stack overflow?
    There's CONFIG_DEBUG_STACK_USAGE but that's unlikely to be much use.

     \ /
      Last update: 2009-05-17 01:17    [W:0.031 / U:67.012 seconds]
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