From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with ESMTP id 488536B0096 for ; Thu, 24 Nov 2011 09:26:16 -0500 (EST) Received: from /spool/local by e7.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 24 Nov 2011 09:26:14 -0500 Received: from d01av04.pok.ibm.com (d01av04.pok.ibm.com [9.56.224.64]) by d01relay04.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id pAOEQAwb326360 for ; Thu, 24 Nov 2011 09:26:10 -0500 Received: from d01av04.pok.ibm.com (loopback [127.0.0.1]) by d01av04.pok.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id pAOEQ7bP026570 for ; Thu, 24 Nov 2011 09:26:09 -0500 Date: Thu, 24 Nov 2011 19:55:07 +0530 From: Srikar Dronamraju Subject: Re: [PATCH v7 3.2-rc2 4/30] uprobes: Define hooks for mmap/munmap. Message-ID: <20111124142507.GI28065@linux.vnet.ibm.com> Reply-To: Srikar Dronamraju References: <20111118110631.10512.73274.sendpatchset@srdronam.in.ibm.com> <20111118110723.10512.66282.sendpatchset@srdronam.in.ibm.com> <1322071812.14799.87.camel@twins> <20111124134742.GH28065@linux.vnet.ibm.com> <1322144017.2921.57.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <1322144017.2921.57.camel@twins> Sender: owner-linux-mm@kvack.org List-ID: To: Peter Zijlstra Cc: Linus Torvalds , Oleg Nesterov , Andrew Morton , LKML , Linux-mm , Ingo Molnar , Andi Kleen , Christoph Hellwig , Steven Rostedt , Roland McGrath , Thomas Gleixner , Masami Hiramatsu , Arnaldo Carvalho de Melo , Anton Arapov , Ananth N Mavinakayanahalli , Jim Keniston , Stephen Wilson , tulasidhard@gmail.com * Peter Zijlstra [2011-11-24 15:13:37]: > On Thu, 2011-11-24 at 19:17 +0530, Srikar Dronamraju wrote: > > * Peter Zijlstra [2011-11-23 19:10:12]: > > > > > On Fri, 2011-11-18 at 16:37 +0530, Srikar Dronamraju wrote: > > > > + ret = install_breakpoint(vma->vm_mm, uprobe); > > > > + if (ret == -EEXIST) { > > > > + atomic_inc(&vma->vm_mm->mm_uprobes_count); > > > > + ret = 0; > > > > + } > > > > > > Aren't you double counting that probe position here? The one that raced > > > you to inserting it will also have incremented that counter, no? > > > > > > > No we arent. > > Because register_uprobe can never race with mmap_uprobe and register > > before mmap_uprobe registers .(Once we start mmap_region, > > register_uprobe waits for the read_lock of mmap_sem.) > > Still doesn't make any sense. Since you don't increment on success, one > has to assume install_breakpoint() will cause an increment. Therefore, > when we encounter -EEXIST we'll already have accounted for this > mm,inode,offset combination. > In the success case, install_breakpoint itself does the increment. We cant allow install_breakpoint to increment in EEXIST case always because doing that in register_uprobe context would increment which is wrong. > But I'll have another look at it, maybe I'm missing something > obvious :-) > > > And we badly need this for mmap_uprobe case. Because when we do mremap, > > or vma_adjust(), we do a munmap_uprobe() followed by mmap_uprobe() which > > would have decremented the count but not removed it. So when we do a > > mmap_uprobe, we need to increment the count. > > Well I see why the count needs to be correct, that's not the issue. Okay .. -- Thanks and Regards Srikar -- 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