Discourage use of pthread_atfork() for call_rcu handlers
RFC PATCH 1/1 Discourage use of pthread_atfork() for call_rcu handlers
Discourage use of glibc pthread_atfork() for call_rcu handlers due to its inappropriate assumptions about single-threadedness while pthread atfork handlers are executing. This results in hangs within the glibc memory allocator.
Signed-off-by Mathieu Desnoyers <[email protected]>
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README +14 -1
@@ -273,7 +273,20 @@ Interaction with fork() must invoke call_rcu_before_fork() before the fork() and call_rcu_after_fork_parent() after the fork(). The child process must invoke call_rcu_after_fork_child(). - These three APIs are suitable for passing to pthread_atfork(). + Even though these three APIs are suitable for passing to + pthread_atfork(), use of pthread_atfork() is *STRONGLY + DISCOURAGED* for programs calling the glibc memory allocator + (malloc(), calloc(), free(), ...) within call_rcu callbacks. + This is due to limitations in the way glibc memory allocator + handles calls to the memory allocator from concurrent threads + while the pthread_atfork() handlers are executing. + Combining e.g.: + * call to free() from callbacks executed within call_rcu worker + threads, + * executing call_rcu atfork handlers within the glibc pthread + atfork mechanism, + will sometimes trigger interesting process hangs. This usually + hangs on a memory allocator lock within glibc. Thread Local Storage (TLS)
Signature · 4 lines
Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com