On Sep 19, 2008, at 4:05 PM, Chase N Douglas wrote:
I believe I have found the issue. Suppose there are threads A and B. Thread A is running and is in the critical section of malloc() where locks are held to manage the heap and such. A context switch then occurs before thread A can relinquish the malloc locks. Thread B now attempts to fork. After forking, the parent process (still thread B) continues as normal, but the new child process immediately attempts to free the manager thread resources as it's no longer needed. At this point, the child process attempts to grab the malloc locks to free the memory, but it sees that someone is holding the lock (what used to be thread A). We now have a deadlock since even if thread A relinquishes the lock, it's in a separate process now with a separate virtual memory space. The lock state in the child process will never be relinquished. For this reason, such locks should be held before forking, the parent process after the fork should relinquish them, and the child process after the fork should reinitialize them.However, there are many locks in uClibc and not a single one is managed in this way before and after forking. Shouldn't every single lock be dealt with before and after forking, or am I missing something here?
After a second glance I see that the only locks this applies to are pthread_mutex_t locks and other types derived from pthread_mutex_t locks. Inside uClibc itself this seems to be only malloc locks and regex locks. I will be trying to put together a patch that will take care of both of these types of locks when forking.
Thanks -- Chase Douglas IBM Linux Technology Center [EMAIL PROTECTED] (614) 456-0455
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