From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with SMTP id E6F089400BF for ; Wed, 5 Oct 2011 13:52:50 -0400 (EDT) Date: Wed, 5 Oct 2011 19:48:42 +0200 From: Oleg Nesterov Subject: Re: [PATCH v5 3.1.0-rc4-tip 12/26] Uprobes: Handle breakpoint and Singlestep Message-ID: <20111005174842.GA3812@redhat.com> References: <20110920115938.25326.93059.sendpatchset@srdronam.in.ibm.com> <20110920120221.25326.74714.sendpatchset@srdronam.in.ibm.com> <1317045553.1763.23.camel@twins> <20110926160144.GC13535@linux.vnet.ibm.com> <1317054322.1763.31.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1317054322.1763.31.camel@twins> Sender: owner-linux-mm@kvack.org List-ID: To: Peter Zijlstra Cc: Srikar Dronamraju , Ingo Molnar , Steven Rostedt , Linux-mm , Arnaldo Carvalho de Melo , Linus Torvalds , Jonathan Corbet , Hugh Dickins , Christoph Hellwig , Masami Hiramatsu , Thomas Gleixner , Ananth N Mavinakayanahalli , Andrew Morton , Jim Keniston , Roland McGrath , Andi Kleen , LKML On 09/26, Peter Zijlstra wrote: > > On Mon, 2011-09-26 at 21:31 +0530, Srikar Dronamraju wrote: > > * Peter Zijlstra [2011-09-26 15:59:13]: > > > > > On Tue, 2011-09-20 at 17:32 +0530, Srikar Dronamraju wrote: > > > > Hence provide some extra > > > > + * time (by way of synchronize_sched() for breakpoint hit threads to acquire > > > > + * the uprobes_treelock before the uprobe is removed from the rbtree. > > > > > > 'Some extra time' doesn't make me all warm an fuzzy inside, but instead > > > screams we fudge around a race condition. > > > > The extra time provided is sufficient to avoid the race. So will modify > > it to mean "sufficient" instead of "some". > > > > Would that suffice? > > Much better, for extra point, explain why its sufficient as well ;-) +1 ;) I can't understand why synchronize_sched helps. In fact it is very possible I simply misunderstood the problem, I'll appreciate if you can explain. Just for example. Suppose that uprobe_notify_resume() sleeps in down_read(mmap_sem). In this case synchronize_sched() can return even before it takes this sem, how this can help the subsequent find_uprobe() ? Or that task can be simply preempted before. Or I missed the point completely? 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