Date: Thu, 20 May 2004 16:11:42 +1000 From: Tim Robbins <tjr@freebsd.org> To: Daniel Eischen <eischen@vigrid.com> Cc: Julian Elischer <julian@elischer.org> Subject: Re: execve() and KSE Message-ID: <20040520061142.GA3493@cat.robbins.dropbear.id.au> In-Reply-To: <Pine.GSO.4.10.10405200111150.20696-100000@pcnet5.pcnet.com> References: <Pine.BSF.4.21.0405192113200.11004-100000@InterJet.elischer.org> <Pine.GSO.4.10.10405200111150.20696-100000@pcnet5.pcnet.com>
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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(); } Tim
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