Date: Wed, 11 Apr 2012 17:47:03 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Ian Lepore <freebsd@damnhippie.dyndns.org> Cc: FreeBSD Hackers <freebsd-hackers@freebsd.org>, Mel Flynn <rflynn@acsalaska.net> Subject: Re: Debugging zombies: pthread_sigmask and sigwait Message-ID: <20120411144703.GM2358@deviant.kiev.zoral.com.ua> In-Reply-To: <1334154373.1082.110.camel@revolution.hippie.lan> References: <4F859112.5070005@acsalaska.net> <1334154373.1082.110.camel@revolution.hippie.lan>
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--EontnEYYSB34MdTw Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Apr 11, 2012 at 08:26:13AM -0600, Ian Lepore wrote: > On Wed, 2012-04-11 at 16:11 +0200, Mel Flynn wrote: > > Hi, > >=20 > > I'm currently stuck on a bug in Zarafa-spooler that creates zombies. and > > working around it by claiming that our pthread library isn't "normal" > > which uses standard signals rather then a signal thread. > >=20 > > My limited understanding of these facilities is however not enough to > > see the actual problem here and reading of related manpages did not lead > > me to a solution either. A test case reproducing the problem is attache= d. > >=20 > > What happens is that SIGCHLD is never received by the signal thread and > > the child processes turn to zombies. Signal counters never go up, not > > even for SIGINFO, which I added specifically to see if anything gets > > through at all. > >=20 > > The signal thread shows being stuck in sigwait. It's reproducible on > > 8.3-PRERELEASE of a few days ago (r233768). I'm not able to test it on > > anything newer unfortunately, but I suspect this is a bug/linuxism in > > the code not in FreeBSD. > >=20 > > Thanks in advance for any insights. > > _______________________________________________ > > freebsd-hackers@freebsd.org mailing list > > http://lists.freebsd.org/mailman/listinfo/freebsd-hackers > > To unsubscribe, send any mail to "freebsd-hackers-unsubscribe@freebsd.o= rg" >=20 > The signal mask for a new thread is inherited from the parent thread. > In your example code, the signal handling thread inherits the blocked > status of the signals as set up in main(). Try adding this line to > signal_handler() before it goes into its while() loop: >=20 > pthread_sigmask(SIG_UNBLOCK, &signal_mask, NULL); This is completely wrong. sigwait(2) requires the waited signals to be blocked, so the code is right in this regard. What happens, as I guess it, the SIGINFO and SIGCHLD are ignored, so kernel do not even bother to queue the signals to the master process. Register a dummy signal handler for your signals with sigaction before creating 'signal_handler' thread. --EontnEYYSB34MdTw Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (FreeBSD) iEYEARECAAYFAk+FmWcACgkQC3+MBN1Mb4g21wCfe9r+dXNxfVNllIS5PYUc+Qdb ELcAn3lVshYCjbPyxtQMb/2vosmK2d8l =+hSJ -----END PGP SIGNATURE----- --EontnEYYSB34MdTw--
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