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From Jim Jagielski <...@jaguNET.com>
Subject Re: Issues/questions with apr_memcache_multigetp
Date Wed, 23 Sep 2015 19:48:30 GMT
Haven't looked at the actual bug but yet, in general, we appreciate
it when people send in patches that fix bugs or errors in our code
instead of simply forking off those changes.

Apache tries to work a little bit differently than the current buzz
about forking and working in isolation; we instead encourage people
to collaborate w/ the actual project itself, submitting bug reports
and patches, and working as a cohesive group, rather than scattered
islands of code :)

Thx!

> On Sep 23, 2015, at 3:23 PM, Jeffrey Crowell <jcrowell@google.com> wrote:
> 
> Hi,
> 
> I work on mod_pagespeed, where we use a forked version of apr_memcache.c (https://github.com/pagespeed/mod_pagespeed/blob/master/third_party/aprutil/apr_memcache2.c)
to interact with memcached.
> 
> Recently we've become aware of a bug where we end up hanging in apr_memcache2_multigetp,
pinning cpu at 100%.
> 
> We have some patches which were created in an attempt to fix some signed bugs in the
original code that I think may be causing our issue.
> 
> Namely here: https://github.com/pagespeed/mod_pagespeed/blob/master/third_party/aprutil/apr_memcache2.c#L1453
 vs here https://gist.github.com/crowell/59bfa1bb9f0cda30c48a#file-multiget-c-L192
> The original code uses an atoi(), which has undefined behavior when called on non integer
strings, leaving len to be 0.
> 
> Second, the check here https://github.com/pagespeed/mod_pagespeed/blob/master/third_party/aprutil/apr_memcache2.c#L1457
vs https://gist.github.com/crowell/59bfa1bb9f0cda30c48a#file-multiget-c-L199
> 
> In the original apr code, this check will never fail. len is an apr_size_t, and will
never be < 0.
> 
> The issue here now is that the check in the "server sent back a key that i didn't ask
for" https://github.com/pagespeed/mod_pagespeed/blob/master/third_party/aprutil/apr_memcache2.c#L1507
(same in both forked and upstream), apr_pollset_remove, is never called, and the number of
queries sent is never changed.
> 
> Does it seem possible that this is causing the server to spin here, and would apr be
interested in accepting a patch to fix the signedness issues?
> 
> Thanks,
> Jeff


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