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 984086B0096 for ; Thu, 24 Nov 2011 09:13:59 -0500 (EST) Message-ID: <1322144017.2921.57.camel@twins> Subject: Re: [PATCH v7 3.2-rc2 4/30] uprobes: Define hooks for mmap/munmap. From: Peter Zijlstra Date: Thu, 24 Nov 2011 15:13:37 +0100 In-Reply-To: <20111124134742.GH28065@linux.vnet.ibm.com> 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> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Mime-Version: 1.0 Sender: owner-linux-mm@kvack.org List-ID: To: Srikar Dronamraju 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 On Thu, 2011-11-24 at 19:17 +0530, Srikar Dronamraju wrote: > * Peter Zijlstra [2011-11-23 19:10:12]: >=20 > > On Fri, 2011-11-18 at 16:37 +0530, Srikar Dronamraju wrote: > > > + ret =3D install_breakpoint(vma->vm_mm, uprobe= ); > > > + if (ret =3D=3D -EEXIST) { > > > + atomic_inc(&vma->vm_mm->mm_uprobes_co= unt); > > > + ret =3D 0; > > > + }=20 > >=20 > > Aren't you double counting that probe position here? The one that raced > > you to inserting it will also have incremented that counter, no? > >=20 >=20 > 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. 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.=20 Well I see why the count needs to be correct, that's not the issue. -- 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