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Re: RFC: Deadlock in multithreaded application when doing IO and fork.

On 02/01/2013 12:02 AM, Carlos O'Donell wrote:
another thread could be inside malloc and trigger an
assertion or debug output, which will block, and
deadlock fork() e.g.

T1			T2
take list_all_lock
			calls malloc
			takes arena lock.
			malloc aborts and tries to do IO.
			user define malloc tries to do IO.
			blocks on list_all_lock.
blocks on arena lock

The bug discussed in this old thread is now fixed on master, with commit 29d794863cd6e03115d3670707cc873a9965ba92.

IMO, the deadlock you describe is not relevant because list_all_lock is only taken on fflush (NULL) or if a stdio stream is opened or closed. abort does not flush the streams under list_all_lock (ugh). Opening or closing a stdio stream performs malloc or free, so it will potentially deadlock even without the presence of list_all_lock, just involving the malloc locks. A malloc calling into stdio is just undefined. We get away with it to some extent because we implement both, but an interposed malloc cannot do this.


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