Date: Tue, 2 Sep 2008 16:59:07 +0300 From: Kostik Belousov <kostikbel@gmail.com> To: David Xu <davidxu@freebsd.org> Cc: Daniel Eischen <deischen@freebsd.org>, Andriy Gapon <avg@icyb.net.ua>, freebsd-threads@freebsd.org Subject: Re: mysterious hang in pthread_create Message-ID: <20080902135907.GX2038@deviant.kiev.zoral.com.ua> In-Reply-To: <48BC990C.9020208@freebsd.org> References: <Pine.GSO.4.64.0808301200460.9898@sea.ntplx.net> <20080830184512.GH2038@deviant.kiev.zoral.com.ua> <48BBA369.9010108@freebsd.org> <48BBA925.1000303@icyb.net.ua> <20080901084548.GQ2038@deviant.kiev.zoral.com.ua> <48BBC9A3.1050905@icyb.net.ua> <20080901111215.GS2038@deviant.kiev.zoral.com.ua> <48BBDD6A.60002@icyb.net.ua> <20080901131724.GT2038@deviant.kiev.zoral.com.ua> <48BC990C.9020208@freebsd.org>
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--Wk+D4bxjv0bBail9 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Sep 02, 2008 at 09:38:20AM +0800, David Xu wrote: > Kostik Belousov wrote: > >On Mon, Sep 01, 2008 at 03:17:46PM +0300, Andriy Gapon wrote: > >>on 01/09/2008 14:12 Kostik Belousov said the following: > >>>On Mon, Sep 01, 2008 at 01:53:23PM +0300, Andriy Gapon wrote: > >... > >>>>>>>The following silly patch fixes the problem Andriy encountered: > >>>>>>I can confirm - this fixed the issue for me. > >>>>>>David, thanks! > >>>>>Does libc_r still work with patch applied ? > >>>>In what sense? > >>>>The test program that I posted seems to hang in both cases (patched a= nd=20 > >>>>unpatched rtld). > >>>The David' patch changes the code used to support libc_r operations. > >>>Even on CURRENT, if you run 4.x-compiled binary with the support of > >>>compat-4x libraries, this code from /libexec/ld-elf.so.1 (installed > >>>by CURRENT buildworld) provides locking for rtld. > >>I understand, but I am not sure what exactly needs to be tested. > >>"Still works" is too broad in this context. > > > >I am not sure too. As I said, this one of the reason I prefered to not > >touch that code. >=20 > It should not affect other code outside the rtld. In fact, this patch > fixes the maintenance of synchronization between locks and thread_flag. > In current code, if you acquire a rwlock, and then acquire second > rwlock, the first one will work, but acquiring second lock will fail > and thread_flag is out of sync, this results bit flag leaking in > thread_flag, and later a _rtld_thread_init() call will transfer the > unlocked rwlock state to libthr as locked state, also the existing > code does not distinguish reader lock and writer lock, it blindly=20 > transfer lock state as write-lock, fortunately, in correct case, > it should not be called with any lock held, so the transferring > does not occur. Yes, I understand this. And, this code is used when threading implementation is provided by libc_r, see above. I have no objection against that patch, but I think that it shall be verified whether compat-4x threaded programs work correctly with the change. > Another question is why should dl_iterate_phdr() use exclusive lock ? > doesn't this cause all C++ exception to be executed in serialization > manner ? It is required by C++ runtime. See the commit log for r178807. --Wk+D4bxjv0bBail9 Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (FreeBSD) iEYEARECAAYFAki9RqsACgkQC3+MBN1Mb4iTcQCgnkiWRz0LubydR3GBUgg+aKnV sFwAoOsJyPFdUXasAwocFjj1MUaI7vCA =OJp8 -----END PGP SIGNATURE----- --Wk+D4bxjv0bBail9--
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