zend api header was changed zend_class_entry definition.
simply mark the free in zend/zend_opcode.c at 295 and 328
str_free(ce->name) or efree 
name has been changed from char to const char.

In the patch supplied we duplicate ce->name and info->name as otherwise they 
would be freed twice - by interned storage shutdown and by ZE.

This bug has been fixed in SVN.

Snapshots of the sources are packaged every three hours; this change
will be in the next snapshot. You can grab the snapshot at
http://snaps.php.net/.

 For Windows:

http://windows.php.net/snapshots/
 
Thank you for the report, and for helping us make PHP better.

This bug might still not be fixed; at least if it is indeed the same as #61236. I tried trunk revision at 323991. (This is on x86_64 Linux)

This needs further fixing as the issue behaves different way on TS and NTS. 
Currently interned strings are only handled on NTS builds.

building php 54 from sources,

	svn info
		Path: .
		URL: https://svn.php.net/repository/php/php-src/branches/PHP_5_4
		Repository Root: https://svn.php.net/repository
		Repository UUID: c90b9560-bf6c-de11-be94-00142212c4b1
		Revision: 324092
		Node Kind: directory
		Schedule: normal
		Last Changed Author: cataphract
		Last Changed Rev: 324082
		Last Changed Date: 2012-03-10 09:19:39 -0800 (Sat, 10 Mar 2012)

with gcc version 4.6.3 (SUSE Linux) on x86_64-suse-linux,

	php -v
		PHP 5.4.1RC1-dev (cli) (built: Mar 10 2012 20:21:53)
		Copyright (c) 1997-2012 The PHP Group
		Zend Engine v2.4.0, Copyright (c) 1998-2012 Zend Technologies
		    with Xdebug v2.2.0-dev, Copyright (c) 2002-2012, by Derick Rethans

co of APC trunk sources

	svn co http://svn.php.net/repository/pecl/apc/trunk apc
	svn info
		Path: .
		URL: http://svn.php.net/repository/pecl/apc/trunk
		Repository Root: http://svn.php.net/repository
		Repository UUID: c90b9560-bf6c-de11-be94-00142212c4b1
		Revision: 324092
		Node Kind: directory
		Schedule: normal
		Last Changed Author: pajoye
		Last Changed Rev: 324037
		Last Changed Date: 2012-03-08 16:01:32 -0800 (Thu, 08 Mar 2012)

attemtping the patch,

	wget -k -O /usr/local/src/interned_string_double_free_fix.patch.TRUNK "https://bugs.php.net/patch-display.php?bug_id=61238&patch=interned_string_double_free_fix&revision=1331026333&download=1"

	cd apc
	patch -p0 < ../interned_string_double_free_fix.patch

		patching file apc_zend.h
		Reversed (or previously applied) patch detected!  Assume -R? [n]^C

looks applied already

@ build

	phpize
	./configure --prefix=/usr/local/apc -enable-apc
	make -j20

		Build complete.
		Don't forget to run 'make test'.

then testing

	grep enable php5/conf.d/apc.ini
		apc.enabled="1"
		apc.enable_cli="1"
	make test
		*** glibc detected *** /usr/local/php5/bin/php: double free or corruption (out): 0x00007f5c116ded30 ***
		======= Backtrace: =========
		/lib64/libc.so.6(+0x74c06)[0x7f5c0fb94c06]
		/usr/local/php5/bin/php(destroy_zend_class+0x23d)[0x5abddd]
		/usr/local/php5/bin/php(zend_hash_clean+0x68)[0x5c3bc8]
		/usr/local/src/apc/modules/apc.so(apc_interned_strings_shutdown+0x20)[0x7f5c0f48b940]
		/usr/local/src/apc/modules/apc.so(apc_module_shutdown+0x12d)[0x7f5c0f48514d]
		/usr/local/src/apc/modules/apc.so(+0xb78f)[0x7f5c0f47a78f]
		/usr/local/php5/bin/php[0x5bd1b3]
		/usr/local/php5/bin/php[0x5c2494]
		/usr/local/php5/bin/php(zend_hash_graceful_reverse_destroy+0x28)[0x5c3ca8]
		/usr/local/php5/bin/php[0x5b5b3e]
		/usr/local/php5/bin/php(php_module_shutdown+0x25)[0x553a65]
		/usr/local/php5/bin/php[0x420405]
		/lib64/libc.so.6(__libc_start_main+0xed)[0x7f5c0fb4123d]
		/usr/local/php5/bin/php[0x4205e1]
		======= Memory map: ========
		00400000-00742000 r-xp 00000000 fd:04 2621493                            /usr/local/php5/bin/php
		00942000-009c7000 r--p 00342000 fd:04 2621493                            /usr/local/php5/bin/php
		009c7000-009cb000 rw-p 003c7000 fd:04 2621493                            /usr/local/php5/bin/php
		009cb000-00af0000 rw-p 00000000 00:00 0                                  [heap]
		7f5c06e56000-7f5c0ee56000 rw-s 00000000 00:12 7440333                    /tmp/apc.EfDVAW (deleted)
		7f5c0ee56000-7f5c0efeb000 r-xp 00000000 fd:04 7210289                    /usr/local/ssl/lib/libcrypto.so.1.0.0
		7f5c0efeb000-7f5c0f1eb000 ---p 00195000 fd:04 7210289                    /usr/local/ssl/lib/libcrypto.so.1.0.0
		7f5c0f1eb000-7f5c0f204000 r--p 00195000 fd:04 7210289                    /usr/local/ssl/lib/libcrypto.so.1.0.0
		...

The supplied patch interned_string_double_free_fix2 completely disables interned 
string handling in TS builds reverting the previous patch (which is already 
commited). This way APC stays compatible with ZE where inderned strings are 
ignored as well.

applying "interned_string_double_free_fix2" patch to apc/trunk w/ php5.4,

...
make test
	=====================================================================
	TEST RESULT SUMMARY
	---------------------------------------------------------------------
	Exts skipped    :    0
	Exts tested     :   13
	---------------------------------------------------------------------

	Number of tests :   26                25
	Tests skipped   :    1 (  3.8%) --------
	Tests warned    :    0 (  0.0%) (  0.0%)
	Tests failed    :    0 (  0.0%) (  0.0%)
	Expected fail   :    0 (  0.0%) (  0.0%)
	Tests passed    :   25 ( 96.2%) (100.0%)
	---------------------------------------------------------------------
	Time taken      :    1 seconds
	=====================================================================

php -i | grep -i apc | head -n 3
	Additional .ini files parsed => /usr/local/etc/php5/conf.d/apc.ini,
	apc
	APC Support => enabled

thank you

This bug has been fixed in SVN.

Snapshots of the sources are packaged every three hours; this change
will be in the next snapshot. You can grab the snapshot at
http://snaps.php.net/.

 For Windows:

http://windows.php.net/snapshots/
 
Thank you for the report, and for helping us make PHP better.

I am still seeing this bug in a brand new PHP 5.4.4 build with APC freshly built 
via pecl. Is this fix included in 5.4.4 and the latest APC? If not, what has to 
happen to move it past the "fixed in SVN" stage to the "available standard" stage? 
Thanks.

A whole week where I have nothing else to do, a computer and a loop of some good house music.

The last time I had to debug things similarly, I had to patch valgrind to report back on memory overwrites & run almost 100k randomly ordered requests.

I wish fixing APC was my day job again :(

I hear you! But what about the fix already committed in svn? Does it just need 
publication as part of a new release or is there some problem with that fix not 
reflected here in the ticket?

We have a few more issues to track down before we are ready for a release. 
Install from SVN for now. It is trivial to do:

svn checkout http://svn.php.net:/repository/pecl/apc/trunk apc
cd apc
phpize
./configure --enable-apc-pthreadrwlocks
make 
make install

OK, that's what I'll do for now. Thanks.