From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751969Ab1I0NYO (ORCPT ); Tue, 27 Sep 2011 09:24:14 -0400 Received: from e7.ny.us.ibm.com ([32.97.182.137]:59564 "EHLO e7.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751298Ab1I0NYN (ORCPT ); Tue, 27 Sep 2011 09:24:13 -0400 Date: Tue, 27 Sep 2011 18:38:50 +0530 From: Srikar Dronamraju To: Peter Zijlstra Cc: Ingo Molnar , Steven Rostedt , Linux-mm , Arnaldo Carvalho de Melo , Linus Torvalds , Ananth N Mavinakayanahalli , Hugh Dickins , Christoph Hellwig , Jonathan Corbet , Thomas Gleixner , Masami Hiramatsu , Oleg Nesterov , Andrew Morton , Jim Keniston , Roland McGrath , Andi Kleen , LKML Subject: Re: [PATCH v5 3.1.0-rc4-tip 4/26] uprobes: Define hooks for mmap/munmap. Message-ID: <20110927130850.GD3685@linux.vnet.ibm.com> Reply-To: Srikar Dronamraju References: <20110920115938.25326.93059.sendpatchset@srdronam.in.ibm.com> <20110920120040.25326.63549.sendpatchset@srdronam.in.ibm.com> <1317045191.1763.22.camel@twins> <20110926154414.GB13535@linux.vnet.ibm.com> <1317123435.15383.33.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <1317123435.15383.33.camel@twins> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Peter Zijlstra [2011-09-27 13:37:15]: > On Mon, 2011-09-26 at 21:14 +0530, Srikar Dronamraju wrote: > > > > > > + > > > > +/* > > > > + * Called from mmap_region. > > > > + * called with mm->mmap_sem acquired. > > > > + * > > > > + * Return -ve no if we fail to insert probes and we cannot > > > > + * bail-out. > > > > + * Return 0 otherwise. i.e : > > > > + * - successful insertion of probes > > > > + * - (or) no possible probes to be inserted. > > > > + * - (or) insertion of probes failed but we can bail-out. > > > > + */ > > > > +int mmap_uprobe(struct vm_area_struct *vma) > > > > +{ > > > > + struct list_head tmp_list; > > > > + struct uprobe *uprobe, *u; > > > > + struct inode *inode; > > > > + int ret = 0; > > > > + > > > > + if (!valid_vma(vma)) > > > > + return ret; /* Bail-out */ > > > > + > > > > + inode = igrab(vma->vm_file->f_mapping->host); > > > > + if (!inode) > > > > + return ret; > > > > + > > > > + INIT_LIST_HEAD(&tmp_list); > > > > + mutex_lock(&uprobes_mmap_mutex); > > > > + build_probe_list(inode, &tmp_list); > > > > + list_for_each_entry_safe(uprobe, u, &tmp_list, pending_list) { > > > > + loff_t vaddr; > > > > + > > > > + list_del(&uprobe->pending_list); > > > > + if (!ret && uprobe->consumers) { > > > > + vaddr = vma->vm_start + uprobe->offset; > > > > + vaddr -= vma->vm_pgoff << PAGE_SHIFT; > > > > + if (vaddr < vma->vm_start || vaddr >= vma->vm_end) > > > > + continue; > > > > + ret = install_breakpoint(vma->vm_mm, uprobe); > > > > + > > > > + if (ret && (ret == -ESRCH || ret == -EEXIST)) > > > > + ret = 0; > > > > + } > > > > + put_uprobe(uprobe); > > > > + } > > > > + > > > > + mutex_unlock(&uprobes_mmap_mutex); > > > > + iput(inode); > > > > + return ret; > > > > +} > > > > + > > > > +static void dec_mm_uprobes_count(struct vm_area_struct *vma, > > > > + struct inode *inode) > > > > +{ > > > > + struct uprobe *uprobe; > > > > + struct rb_node *n; > > > > + unsigned long flags; > > > > + > > > > + n = uprobes_tree.rb_node; > > > > + spin_lock_irqsave(&uprobes_treelock, flags); > > > > + uprobe = __find_uprobe(inode, 0, &n); > > > > + > > > > + /* > > > > + * If indeed there is a probe for the inode and with offset zero, > > > > + * then lets release its reference. (ref got thro __find_uprobe) > > > > + */ > > > > + if (uprobe) > > > > + put_uprobe(uprobe); > > > > + for (; n; n = rb_next(n)) { > > > > + loff_t vaddr; > > > > + > > > > + uprobe = rb_entry(n, struct uprobe, rb_node); > > > > + if (uprobe->inode != inode) > > > > + break; > > > > + vaddr = vma->vm_start + uprobe->offset; > > > > + vaddr -= vma->vm_pgoff << PAGE_SHIFT; > > > > + if (vaddr < vma->vm_start || vaddr >= vma->vm_end) > > > > + continue; > > > > + atomic_dec(&vma->vm_mm->mm_uprobes_count); > > > > + } > > > > + spin_unlock_irqrestore(&uprobes_treelock, flags); > > > > +} > > > > + > > > > +/* > > > > + * Called in context of a munmap of a vma. > > > > + */ > > > > +void munmap_uprobe(struct vm_area_struct *vma) > > > > +{ > > > > + struct inode *inode; > > > > + > > > > + if (!valid_vma(vma)) > > > > + return; /* Bail-out */ > > > > + > > > > + if (!atomic_read(&vma->vm_mm->mm_uprobes_count)) > > > > + return; > > > > + > > > > + inode = igrab(vma->vm_file->f_mapping->host); > > > > + if (!inode) > > > > + return; > > > > + > > > > + dec_mm_uprobes_count(vma, inode); > > > > + iput(inode); > > > > + return; > > > > +} > > > > > > One has to wonder why mmap_uprobe() can be one function but > > > munmap_uprobe() cannot. > > > > > > > I didnt understand this comment, Can you please elaborate? > > mmap_uprobe uses build_probe_list and munmap_uprobe uses > > dec_mm_uprobes_count. > > Ah, I missed build_probe_list(), but I didn't see a reason for the > existence of dec_mm_uprobe_count(), the name doesn't make sense and the > content is 'small' enough to just put in munmap_uprobe. > > To me it looks similar to the list iteration you have in mmap_uprobe(), > you didn't split that out into another function either. Hmm, For me whats done in dec_mm_uprobe_count() is similar to whats done in build_probe_list(), just that build_probe_list does a atomic_inc + list_add while dec_mm_uprobe_count() does a atomic_dec. When I kept dec_mm_uprobe_count() inside munmap_uprobe(), I found most of the code nested too deep. Hence carved it out as a separate function. I open to suggestions for dec_mm_uprobe_count() -- Thanks and Regards Srikar