Date: Mon, 9 May 2011 19:39:46 +0400 From: Max Brazhnikov <makc@issp.ac.ru> To: Kostik Belousov <kostikbel@gmail.com> Cc: freebsd-stable@freebsd.org Subject: Re: automoc4 processes lock again Message-ID: <201105091939.47230.makc@issp.ac.ru> In-Reply-To: <20110509124104.GF48734@deviant.kiev.zoral.com.ua> References: <201105091240.57785.makc@issp.ac.ru> <20110509124104.GF48734@deviant.kiev.zoral.com.ua>
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On Mon, 9 May 2011 15:41:05 +0300, Kostik Belousov wrote: > You did not supplied enough information. > Which of the processes is parent, which is child ? > Note that there are other threads in the pid 18636. What does they do ? Here is backtraces from all threads http://people.freebsd.org/~makc/automoc4.bt 63373 is a parent now, 63374 is a child. There were no related changes in Qt4 and automoc4 sources, probably my update from 8.2-PRERELEASE to STABLE a week ago triggered the issue. > If you would allow me to make some guess, then I could assume that pid > 18640 is the child. Note that the child is waiting for the pthread > mutex locked which protects the stdio' FILE structure. Now, assume > additionally that the parent had the FILE locked in one thread while > another thread did the fork. Then, the child process would never be able > to obtain the lock because the lock was acquired by the thread that > exists no longer (in the child process, only the thread that called > fork is duplicated). > > In fact, I believe that you already reported a similar problem with > malloc(3) some time ago. The root of the problem would be an undefined > (and permitted by POSIX) behaviour of calling non-async signal safe > functions in multithreaded process after fork. > > For malloc(3), this can be argued to be a quality of the implementation > issue, but there is no reason to specially handle random mutexes, even > from libc. If the mutex was locked during the fork time, the protected > data structure is arguably in the inconsistent state after the fork in > the child.
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