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

[Florian Weimer]

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
> fork
> take list_all_lock
> 			calls malloc
> 			takes arena lock.
> 			malloc aborts and tries to do IO.
> 				or
> 			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.

Florian