Date: Wed, 24 Oct 2007 19:34:18 -0700 From: Alfred Perlstein <alfred@freebsd.org> To: David Xu <davidxu@FreeBSD.org> Cc: cvs-src@FreeBSD.org, src-committers@FreeBSD.org, Julian Elischer <julian@FreeBSD.org>, cvs-all@FreeBSD.org Subject: Re: cvs commit: src/sys/kern kern_fork.c Message-ID: <20071025023418.GR33488@elvis.mu.org> In-Reply-To: <47200064.9050403@freebsd.org> References: <200710231754.l9NHsGLH090312@repoman.freebsd.org> <471FF2BE.9000204@freebsd.org> <20071025022607.GQ33488@elvis.mu.org> <47200064.9050403@freebsd.org>
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* David Xu <davidxu@FreeBSD.org> [071024 19:32] wrote: > Alfred Perlstein wrote: > >* David Xu <davidxu@FreeBSD.org> [071024 18:34] wrote: > > > >>Julian Elischer wrote: > >> > >>>julian 2007-10-23 17:54:16 UTC > >>> > >>>FreeBSD src repository > >>> > >>>Modified files: > >>> sys/kern kern_fork.c > >>>Log: > >>>Take out the single-threading code in fork. > >>>After discussions with jeff, alc, (various Ironport people), david Xu, > >>>and mostly Alfred (who found the problem) it has been demonstrated that > >>>this > >>>is not needed for our implementations of threads and represents a real > >>>(as in we've seen it happen a lot) deadlock danger. > >>>... > >> > >>I think if process is forking a thread, that says flag RFPROC is not > >>set and flags RFCFDG or RFCFDG is set, you still need to call > >>thread_single(SINGLE_BOUNDARY), otherwise, for a threaded process, > >>the memory pointed by p_fd is freed while other threads are using it, > >>it will cause kernel to panic. > > > > > >This is unlikely to be fixed by SINGLE_BOUNDARY and will likely require > >refcounting to fix. SINGLE_BOUNDARY will not fix the locations where > >this happens: > > > > p = td->td_proc; > > fdp = p->p_fd; > > do something that blocks... > > re-use fdp. > > > thread_suspend_check() with SINGLE_BOUNDARY is used is only called > in userret() where I don't think any code is still using the p_fd. This is not an acceptable solution as it will deadlock unless all threads exit the kernel. filedescs can be refcounted per thread I think. -- - Alfred Perlstein
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