From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp2.linux-foundation.org (smtp2.linux-foundation.org [207.189.120.14]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "smtp.linux-foundation.org", Issuer "CA Cert Signing Authority" (verified OK)) by ozlabs.org (Postfix) with ESMTP id BBB1DDDF94 for ; Sat, 9 Jun 2007 05:32:44 +1000 (EST) Date: Fri, 8 Jun 2007 12:32:30 -0700 From: Andrew Morton To: will_schmidt@vnet.ibm.com Subject: Re: [PATCH 1/3] [PATCH i386] during VM oom condition, kill all threads in process group Message-Id: <20070608123230.520655f5.akpm@linux-foundation.org> In-Reply-To: <1181330358.21409.31.camel@farscape.rchland.ibm.com> References: <20070605174831.21740.33119.stgit@farscape.rchland.ibm.com> <20070607153459.2a1b3230.akpm@linux-foundation.org> <20070607231621.GB32549@kryten> <20070607171018.d51fc5da.akpm@linux-foundation.org> <1181330358.21409.31.camel@farscape.rchland.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Cc: linuxppc-dev@ozlabs.org, "Eric W. Biederman" , Oleg Nesterov , Anton Blanchard , linux-kernel@vger.kernel.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Fri, 08 Jun 2007 14:19:18 -0500 Will Schmidt wrote: > > > > zap_other_threads() requires tasklist_lock. > > Yup, I missed that. Thanks for pointing it out. > > > > > > > > > If we're going to do this then we should probably create some new function > > > > (with a better name) which takes tasklsit_lock and then calls > > > > zap_other_threads(). > > I expect this will be a write_lock_irq() since zap_other_threads will be > doing a bit more than just reading the task info. No, I think read_lock() will be sufficient. In fact, it's probably the case that rcu_read_lock() is now sufficient locking coverage for zap_other_threads() (cc's people). It had better be, because do_group_exit() forgot to take tasklist_lock. It is perhaps relying upon spin_lock()'s hidden rcu_read_lock() properties without so much as a code comment, which would be somewhat nasty of it. You could perhaps just call do_group_exit() from within the fault handler, btw. > This will be down in a do-page-fault failure path (see > arch/*/mm/fault.c). I wonder if calling write_lock is going to be safe, > or if its possible to get into a deadlock? i.e. should I branch back up > to the survive: label if I can't take the lock? Would that even be > sufficient? or is it not an issue here? You can take the lock in the fault handler. Nobody should be getting pagefaults while holding tasklist_lock. (Well, a vmalloc fault might, but that's a special-case which doesn't allocate memory or anything like that).