Date: Mon, 9 May 2011 19:58:58 +0300 From: Kostik Belousov <kostikbel@gmail.com> To: Max Brazhnikov <makc@issp.ac.ru> Cc: freebsd-stable@freebsd.org Subject: Re: automoc4 processes lock again Message-ID: <20110509165858.GG48734@deviant.kiev.zoral.com.ua> In-Reply-To: <201105091939.47230.makc@issp.ac.ru> References: <201105091240.57785.makc@issp.ac.ru> <20110509124104.GF48734@deviant.kiev.zoral.com.ua> <201105091939.47230.makc@issp.ac.ru>
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--wthRHICJPcnPKmvQ Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, May 09, 2011 at 07:39:46PM +0400, Max Brazhnikov wrote: > 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 ? >=20 > Here is backtraces from all threads http://people.freebsd.org/~makc/autom= oc4.bt > 63373 is a parent now, 63374 is a child. >=20 > There were no related changes in Qt4 and automoc4 sources, probably my up= date from 8.2-PRERELEASE to STABLE a week ago triggered the issue. It is obviously application bug, yes, I think my guess was right. Thou shalt not call non-async safe functions in thy child of multithreaded process. Since it is a race, I see it more curious that it did not manifested itself prevously. >=20 > > 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). > >=20 > > 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. > >=20 > > 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. --wthRHICJPcnPKmvQ Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (FreeBSD) iEYEARECAAYFAk3IHVEACgkQC3+MBN1Mb4hkfwCdHFLpK//7Je2urHljp+3BmO73 +9gAnR9EuW0Ux0+JOnH761vtanXJvAf+ =7fg5 -----END PGP SIGNATURE----- --wthRHICJPcnPKmvQ--
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