torsten.foertsch at gmx
Nov 14, 2011, 6:26 AM
Views: 1848
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On Monday, 14 November 2011 04:42:16 Max Barry wrote:
> Here is the result:
>
> http://pastebin.com/YDbmq84w
>
> This shows me:
> * running the Apache benchmarking utility to generate lots of requests
> * identifying a process hung in 'futex_wait' (11447)
> * killing it with SEGV
> * obtaining a stack trace
Thanks Max. It really seems to be a modperl problem. I think there is
either something fishy with modperl_tipool_putback_base() or someone
writes to a location that it doesn't own.
Many of your threads block in modperl_tipool_pop() waiting for an
interpreter to become available:
/* block until an item becomes available */
modperl_tipool_wait(tipool);
In src/modules/perl/modperl_tipool.c in function
modperl_tipool_putback_base() you find these lines:
if (!listp) {
/* XXX: Attempt to putback something that was never there */
modperl_tipool_unlock(tipool);
return;
}
I think the code should not return here but call abort() and dump core
because if it enters the if-block it tries to push back an interpreter
that was not taken from the pool. But why would someone call
modperl_tipool_putback_base if not to release an interpreter. Hence the
interpreter is lost. The other part of the function seems quite
reasonable. So, I think modperl_tipool_putback_base() is sometimes called
with a wrong data pointer and thus leaks interpreters.
Can you install the symbol tables for your modperl and perhaps check the
values of *tipool in the core? I think it is
tipool->size == tipool->in_use == tipool->cfg->max
That would explain the behavior.
BTW, there are IMHO many points about the tipool implementation that can
be improved. Why do we use these lists? Wouldn't it be better to
allocated an array of tipool->cfg->max pointers? Or perhaps an apr_hash_t
in pconf?
Torsten Förtsch
--
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