From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751017Ab1JIMGH (ORCPT ); Sun, 9 Oct 2011 08:06:07 -0400 Received: from e8.ny.us.ibm.com ([32.97.182.138]:33915 "EHLO e8.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750744Ab1JIMGD (ORCPT ); Sun, 9 Oct 2011 08:06:03 -0400 Date: Sun, 9 Oct 2011 17:17:45 +0530 From: Srikar Dronamraju To: Oleg Nesterov Cc: Peter Zijlstra , 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 Subject: Re: [PATCH v5 3.1.0-rc4-tip 18/26] uprobes: slot allocation. Message-ID: <20111009114745.GA6810@linux.vnet.ibm.com> Reply-To: Srikar Dronamraju References: <20110920115938.25326.93059.sendpatchset@srdronam.in.ibm.com> <20110920120335.25326.50673.sendpatchset@srdronam.in.ibm.com> <20111007183740.GC1655@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20111007183740.GC1655@redhat.com> 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 * Oleg Nesterov [2011-10-07 20:37:40]: > On 09/20, Srikar Dronamraju wrote: > > > > - * valid_vma: Verify if the specified vma is an executable vma > > + * valid_vma: Verify if the specified vma is an executable vma, > > + * but not an XOL vma. > > * - Return 1 if the specified virtual address is in an > > - * executable vma. > > + * executable vma, but not in an XOL vma. > > */ > > static bool valid_vma(struct vm_area_struct *vma) > > { > > + struct uprobes_xol_area *area = vma->vm_mm->uprobes_xol_area; > > + > > if (!vma->vm_file) > > return false; > > > > + if (area && (area->vaddr == vma->vm_start)) > > + return false; > > Could you explain why do we need this "but not an XOL vma" check? > xol_vma->vm_file is always NULL, no? > Yes, xol_vma->vm_file is always NULL. previously we used shmem_file_setup before we map the XOL area. However we now use init_creds instead, so this should also change accordingly. Will correct this. > > +static struct uprobes_xol_area *xol_alloc_area(void) > > +{ > > + struct uprobes_xol_area *area = NULL; > > + > > + area = kzalloc(sizeof(*area), GFP_KERNEL); > > + if (unlikely(!area)) > > + return NULL; > > + > > + area->bitmap = kzalloc(BITS_TO_LONGS(UINSNS_PER_PAGE) * sizeof(long), > > + GFP_KERNEL); > > + > > + if (!area->bitmap) > > + goto fail; > > + > > + init_waitqueue_head(&area->wq); > > + spin_lock_init(&area->slot_lock); > > + if (!xol_add_vma(area) && !current->mm->uprobes_xol_area) { > > + task_lock(current); > > + if (!current->mm->uprobes_xol_area) { > > + current->mm->uprobes_xol_area = area; > > + task_unlock(current); > > + return area; > > + } > > + task_unlock(current); > > But you can't rely on task_lock(), you can race with another thread > with the same ->mm. I guess you need mmap_sem or xchg(). Agree, I think its better to use cmpxchg instead of xchg(). Otherwise, (using xchg), I would set area to new value, but the old area might be in use already. So I cant unmap the old area. If I use cmpxchg, I can free up the new area if previous area is non NULL. However setting uprobes_xol_area in xol_add_vma() where we already take mmap_sem for write while maping the xol_area is the best option. > > > static int pre_ssout(struct uprobe *uprobe, struct pt_regs *regs, > > unsigned long vaddr) > > { > > - /* TODO: Yet to be implemented */ > > + if (xol_get_insn_slot(uprobe, vaddr) && !pre_xol(uprobe, regs)) { > > + set_instruction_pointer(regs, current->utask->xol_vaddr); > > set_instruction_pointer() looks unneded, pre_xol() has already changed > regs->ip. > Agree. -- Thanks and Regards Srikar