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From bugzi...@apache.org
Subject [Bug 61558] Apache 2.4.27 crashes often when restarting the service. segfault in libdl-2.24.so or apache2
Date Wed, 27 Sep 2017 13:01:36 GMT
https://bz.apache.org/bugzilla/show_bug.cgi?id=61558

--- Comment #16 from Yann Ylavic <ylavic.dev@gmail.com> ---
(In reply to Joe Orton from comment #14)
> If the problem is that a registered mpm_query hook is a function in a
> now-unloaded DSO then I don't think that keeping a copy of the function
> pointer itself (not the function!) is going to help?

The pointer is cleared (NULL) with pconf, after which ap_unixd_hook_mpm_query()
will return DECLINED insteaf of calling the registered (and now unloaded) mpm
function.

> 
> If we treat the root cause of the crash here as unrelated (looks like memory
> corruption with a crash in apr_pool_destroy?), then fixing the crash in
> logging during apr_destroy_and_exit_process() due to MPM cleanup should be
> fixable by calling apr_hook_deregister_all() at the start of that function?

It's unclear to me whether that's a double fault or not, likely yes.
Maybe a MPM cleanup run while unloaded? Didn't find a potential one
registered...

Early apr_hook_deregister_all() looks like a simpler (and wider) solution, but
don't/can't we have legitimate cleanups (i.e. run in time and/or with no scope
issue) that'd run hooks? If not, I'm all for this!

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