Date: Thu, 20 May 2004 19:14:07 +0800 From: David Xu <davidxu@freebsd.org> To: Tim Robbins <tjr@freebsd.org> Cc: Julian Elischer <julian@elischer.org> Subject: Re: execve() and KSE Message-ID: <40AC92FF.804@freebsd.org> In-Reply-To: <20040520061142.GA3493@cat.robbins.dropbear.id.au> References: <Pine.BSF.4.21.0405192113200.11004-100000@InterJet.elischer.org> <Pine.GSO.4.10.10405200111150.20696-100000@pcnet5.pcnet.com> <20040520061142.GA3493@cat.robbins.dropbear.id.au>
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Tim Robbins wrote: > On Thu, May 20, 2004 at 01:16:15AM -0400, Daniel Eischen wrote: > > >>On Wed, 19 May 2004, Julian Elischer wrote: >> >> >>>What is supposed to happen is that all the execve should stall awaiting >>>all the other kernel threads to abort/suicide and then it should proceed >>>with the execve as per normal. >>>it is possible this doesn't work right.. I haven't tried ti for a LONG >>>time.. >> >>The program is bogus also. First, you can't pass NULL to >>pthread_cond_wait() -- check the return values. Second, >>you can't join to a thread that has done an exec() -- >>the whole process has exec'd. I think you need to do >>this the old fashioned way (fork, exec, wait for child, >>etc). > > > The call to pthread_cond_wait() with a NULL mutex argument was a mistake > but the join was intentional. However, I'm not interested in the program; > I'm more interested in the way the kernel handles the execve() call > (and the general robustness of KSE heading up to 5.3-STABLE.) > > The following patch makes the program do what I would expect: exit, instead > of getting stuck in the "running" state. It clears the P_SINGLE_EXIT and > TDF_SA flags after clearing P_SA in kern_execve(). Without this, the flags > are still set in the single-threaded process that comes out the other > side of the execve() syscall, and it ends up getting stuck in > sched_switch <- choosethread <- thread_exit <- thread_user_enter <- > trap <- calltrap. > > (FWIW: there seems to be another nearby bug: the mtx_unlock(&Giant) call > in the kern_execve() ERESTART case may be erroneous, since I can't see > where Giant is acquired.) > > ==== //depot/user/tjr/freebsd-tjr/src/sys/kern/kern_exec.c#19 - /home/tim/p4/src/sys/kern/kern_exec.c ==== > @@ -264,7 +264,8 @@ > * If we get here all other threads are dead, > * so unset the associated flags and lose KSE mode. > */ > - p->p_flag &= ~P_SA; > + p->p_flag &= ~(P_SA|P_SINGLE_EXIT); > + p->p_singlethread->td_flags &= ~TDF_SA; > td->td_mailbox = NULL; > thread_single_end(); > } > > Good catch, I'd like to see P_SINGLE_EXIT is cleared in kern_thread.c::thread_single_end(). > Tim David Xu
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