Bug #71135 [Com]: Random memory corruption with strings

From: Date: Wed, 13 Sep 2017 01:59:04 +0000
Subject: Bug #71135 [Com]: Random memory corruption with strings
References: 1  Groups: php.bugs 
Request: Send a blank email to php-bugs+get-211111@lists.php.net to get a copy of this message 
Edit report at https://bugs.php.net/bug.php?id=71135&edit=1

 ID:                 71135
 Comment by:         nick at noodles dot net dot nz
 Reported by:        iquito at gmx dot net
 Summary:            Random memory corruption with strings
 Status:             Closed
 Type:               Bug
 Package:            opcache
 Operating System:   Debian Jessie
 PHP Version:        7.0.0
 Assigned To:        laruence
 Block user comment: N
 Private report:     N

 New Comment:

We've always had file cache disabled for what it's worth.


Previous Comments:
------------------------------------------------------------------------
[2017-09-13 01:46:03] jjones at smugmug dot com

Today we've been running tests with "opcache.file_cache=" disabled.  We were using
that feature before.

I have not been able to crash "php-fpm" since making that change, even on a system with a
tightly constrained "interned string buffer" setting.

So IMO if you're using Opcache file backed caching, it's worth trying to run with it
disabled.

------------------------------------------------------------------------
[2017-09-13 01:22:28] nick at noodles dot net dot nz

I'm still seeing problems as well. So far I've disabled huge code pages and changed
opcache to not check timestamps (code deploys now fire an opcache_reset() on each webserver).

Is it possible to disable interned strings?

Also, should we be adding comments to this bug or creating a new one (being that this is closed)?

------------------------------------------------------------------------
[2017-09-12 17:21:51] mike@php.net

After many more tests, it seems it rather depends on the moon phase, because I cannot reproduce
anymore.

Looking into the write of uninitialized bytes next.

------------------------------------------------------------------------
[2017-09-12 13:13:55] mike@php.net

Some valgrind logs:
https://gist.github.com/m6w6/67f71247f5325497a59d4686ba4845ac

------------------------------------------------------------------------
[2017-09-12 12:19:15] mike@php.net

The following patch has been added/updated:

Patch Name: interned_strings_top
Revision:   1505218752
URL:        https://bugs.php.net/patch-display.php?bug=71135&patch=interned_strings_top&revision=1505218752

------------------------------------------------------------------------


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the rest of the comments, please view the bug report online at

    https://bugs.php.net/bug.php?id=71135


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