jmarantz commented on issue #1662: Mod_pagespeed deadlock? URL: https://github.com/apache/incubator-pagespeed-ngx/issues/1662#issuecomment-538104477 Thank you for the backtraces. They reveal this is happening in the shared-memory cache, where multiple processes use a cross-process mutex to access shared memory. I have always been concerned that a process crash, or a SIGKILL while holding onto a shared-memory mutex could make it impossible to release the lock. However the shared-memory cache has been running for probably 7 years now and I've never heard of this actually occurring. If this is just a once in a decade fluke, it might be a reasonable workaround to simply reboot the machine to clear the shm-locks and hopefully you will not be unlucky twice. If, after reboot, the problem re-appears, a workaround is to disable the shared-memory cache, and instead use per-process in-memory LRU caches as your L1s. See https://www.modpagespeed.com/doc/system for details. Hope this helps!
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