Date: Sat, 8 Jul 2006 08:40:38 +0200 (CEST) From: Martin Blapp <mb@imp.ch> To: freebsd-current@freebsd.org Subject: Re: Please help reviewing ! Got another crash because of the ttymodem() / ttyclose() race Message-ID: <20060708081419.W14714@godot.imp.ch> In-Reply-To: <200607072236.55319.jhb@freebsd.org> References: <20060708020700.A14714@godot.imp.ch> <200607072236.55319.jhb@freebsd.org>
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Hi, > Yes.. did you see my reply on the mailing list Ouch ? No I missed that ! Thanks. I just read it. > I'm not sure that the proctree_lock should protect t_pgrp as that is part > of the tty structure, not process groups or session structures. Hmm ? In /usr/src/sys/kern/tty.c:1215 we copy in ttioctl() the pointers of p->p_session and p->p_pgrp to the tty structure. 1215 tp->t_session = p->p_session; 1216 tp->t_pgrp = p->p_pgrp; 1217 SESS_LOCK(p->p_session); It looks to me that we have to protect it with the locks of the process groups or session structures since its only a copy of the pointer, and not an exact copy. Else I wouldn't had any crashes - this is the mess. Or do I understand something completly wrong ? >I think probably it should be protected by Giant for now until the tty subsystem >is locked. Also, the ttyinfo() part will not work since it tries to >acquire a mutex (PGRP_LOCK()) while holding a spin mutex (sched_lock). Ok, fixed. Does it look better now ? Btw. this version is now running for three days without any crashes on four SMP boxes. Rocking stable so far. >perhaps instead we need to expand Giant to cover it until the tty subsystem is >locked? How would you do that ? Martin
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