Apache 2.4 adaptor: release the shared-memory mapping on restart (fixes ENOMEM after ~1 year of graceful restarts)

[mkondratov]

Problem

WOShmem_init() (Adaptor/shmem.c) creates the WOAdaptorState file, unlinks it and mmap()s it. Nothing in the adaptor ever unmaps it.

Apache unloads and reloads every DSO module on a graceful restart (apachectl graceful) or restart (SIGHUP). That resets the module's statics (initCalled), so WebObjects_post_config() runs init_adaptor() again in the same parent process, and each restart leaves one more mapped, nameless file behind.

On a 32-bit server this is a time bomb. Ours (AIX 7.1, httpd 2.4.62 built with -bmaxdata:0x80000000, one logrotate graceful restart a night) fails about once a year:

WOShmem_init(): couldn't map file: Not enough space
init_adaptor(): WOShmem_init() failed
WebObjects_post_config(): Adaptor initialization failed. All requests will be declined.
WebObjects_translate(): declining request due to initialization failure   (x 17,872)

Every WebObjects request answers 500 until Apache is fully stopped and started; apachectl restart keeps the parent process and does not help. svmon -P <apache parent pid> | grep -c "clnt /dev/hd3" shows the leaked mappings growing with every restart (78 after 57 graceful restarts on our box).

Fix

• shmem.c / shmem.h: WOShmem_cleanup() — munmap() + close() + reset the statics. Safe to call when nothing is mapped; children that still hold the old mapping are unaffected.
• Apache2.4/mod_WebObjects.c: after a successful init_adaptor(), register a cleanup on the configuration pool that calls WOShmem_cleanup(). Apache clears that pool before every restart, before the DSO is unloaded (cleanups run LIFO, so ours runs while the module code is still mapped). The configuration-check pass (ap_state_query(AP_SQ_MAIN_STATE) == AP_SQ_MS_CREATE_PRE_CONFIG, which also covers apachectl configtest) now skips initialisation, so it maps nothing; a failed init releases what it mapped.

Verification

Sandbox httpd (prefork, 127.0.0.1:8099) on the same AIX box, 10 × kill -USR1, counting mapped /tmp files in the parent with svmon:

module	before	after 10 graceful restarts	requests still reach the application
stock (4.6.3 build and master code)	3	13	yes
this patch	2	2	yes

Built with gcc 10 against httpd-devel 2.4.62 / apr 1.7.4 headers. The Apache2 and Apache2.2 modules have the same structure and would need the same cleanup registration (ap_state_query is 2.4-only; the older ones would use the apr_pool_userdata idiom); I have only tested 2.4.

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