From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx188.postini.com [74.125.245.188]) by kanga.kvack.org (Postfix) with SMTP id 43A846B0044 for ; Sun, 15 Apr 2012 19:44:56 -0400 (EDT) Date: Mon, 16 Apr 2012 01:44:01 +0200 From: Oleg Nesterov Subject: Re: [RFC 0/6] uprobes: kill uprobes_srcu/uprobe_srcu_id Message-ID: <20120415234401.GA32662@redhat.com> References: <20120405222024.GA19154@redhat.com> <1334409396.2528.100.camel@twins> <20120414205200.GA9083@redhat.com> <1334487062.2528.113.camel@twins> <20120415195351.GA22095@redhat.com> <1334526513.28150.23.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1334526513.28150.23.camel@twins> Sender: owner-linux-mm@kvack.org List-ID: To: Peter Zijlstra Cc: Ingo Molnar , Srikar Dronamraju , Andrew Morton , Linus Torvalds , Ananth N Mavinakayanahalli , Jim Keniston , LKML , Linux-mm , Andi Kleen , Christoph Hellwig , Steven Rostedt , Arnaldo Carvalho de Melo , Masami Hiramatsu , Thomas Gleixner , Anton Arapov I'll write another email tomorrow, just one note... On 04/15, Peter Zijlstra wrote: > > OK, still not seeing how your proposal could work.. consider the below > patch comment, I'm not seeing how is_swbp_at_addr_fast() deals with an > in-progress INT3 while we remove the probe. > > By ensuring the non-race with reg/unreg it will either find the uprobe > (no problem) Yes, > or not find it and not see a breakpoint instruction either, > even though the pending breakpoint was generated by a uprobe (which is > now gone), Yes, > causing a false positive SIGTRAP. No. Please note that if is_swbp_at_addr_fast() sets is_swbp == 0 we restart this insn. (note that we also restart if get_user_pages() fails, this is hopefully is more correct too but minor). > Or am I still not getting it? My experience shows this is very unlikely. I am starting to think I missed something, will re-check. And. I have another reason for down_write() in register/unregister. I am still not sure this is possible (I had no time to try to implement), but it seems to me we can kill the uprobe counter in mm_struct. Oleg. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org