Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757801Ab1CONXW (ORCPT ); Tue, 15 Mar 2011 09:23:22 -0400 Received: from www.tglx.de ([62.245.132.106]:49157 "EHLO www.tglx.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757752Ab1CONXU (ORCPT ); Tue, 15 Mar 2011 09:23:20 -0400 Date: Tue, 15 Mar 2011 14:22:09 +0100 (CET) From: Thomas Gleixner To: Srikar Dronamraju cc: Peter Zijlstra , Ingo Molnar , Steven Rostedt , Linux-mm , Arnaldo Carvalho de Melo , Linus Torvalds , Ananth N Mavinakayanahalli , Christoph Hellwig , Andi Kleen , Masami Hiramatsu , Oleg Nesterov , LKML , Jim Keniston , Roland McGrath , SystemTap , Andrew Morton , "Paul E. McKenney" Subject: Re: [PATCH v2 2.6.38-rc8-tip 3/20] 3: uprobes: Breakground page replacement. In-Reply-To: <20110314133433.27435.49566.sendpatchset@localhost6.localdomain6> Message-ID: References: <20110314133403.27435.7901.sendpatchset@localhost6.localdomain6> <20110314133433.27435.49566.sendpatchset@localhost6.localdomain6> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4192 Lines: 150 On Mon, 14 Mar 2011, Srikar Dronamraju wrote: > +/* > + * Called with tsk->mm->mmap_sem held (either for read or write and > + * with a reference to tsk->mm Hmm, why is holding it for read sufficient? . > + */ > +static int write_opcode(struct task_struct *tsk, struct uprobe * uprobe, > + unsigned long vaddr, uprobe_opcode_t opcode) > +{ > + struct page *old_page, *new_page; > + void *vaddr_old, *vaddr_new; > + struct vm_area_struct *vma; > + spinlock_t *ptl; > + pte_t *orig_pte; > + unsigned long addr; > + int ret = -EINVAL; That initialization is pointless. > + /* Read the page with vaddr into memory */ > + ret = get_user_pages(tsk, tsk->mm, vaddr, 1, 1, 1, &old_page, &vma); > + if (ret <= 0) > + return -EINVAL; > + ret = -EINVAL; > + > + /* > + * check if the page we are interested is read-only mapped > + * Since we are interested in text pages, Our pages of interest > + * should be mapped read-only. > + */ > + if ((vma->vm_flags & (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)) == > + (VM_READ|VM_EXEC)) > + goto put_out; IIRC then text pages are (VM_READ|VM_EXEC) > + /* Allocate a page */ > + new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, vaddr); > + if (!new_page) { > + ret = -ENOMEM; > + goto put_out; > + } > + > + /* > + * lock page will serialize against do_wp_page()'s > + * PageAnon() handling > + */ > + lock_page(old_page); > + /* copy the page now that we've got it stable */ > + vaddr_old = kmap_atomic(old_page, KM_USER0); > + vaddr_new = kmap_atomic(new_page, KM_USER1); > + > + memcpy(vaddr_new, vaddr_old, PAGE_SIZE); > + /* poke the new insn in, ASSUMES we don't cross page boundary */ And what makes sure that we don't ? > + addr = vaddr; > + vaddr &= ~PAGE_MASK; > + memcpy(vaddr_new + vaddr, &opcode, uprobe_opcode_sz); > + > + kunmap_atomic(vaddr_new, KM_USER1); > + kunmap_atomic(vaddr_old, KM_USER0); > + > + orig_pte = page_check_address(old_page, tsk->mm, addr, &ptl, 0); > + if (!orig_pte) > + goto unlock_out; > + pte_unmap_unlock(orig_pte, ptl); > + > + lock_page(new_page); > + if (!anon_vma_prepare(vma)) Why don't you get the error code of anon_vma_prepare()? > + /* flip pages, do_wp_page() will fail pte_same() and bail */ -ENOPARSE > + ret = replace_page(vma, old_page, new_page, *orig_pte); > + > + unlock_page(new_page); > + if (ret != 0) > + page_cache_release(new_page); > +unlock_out: > + unlock_page(old_page); > + > +put_out: > + put_page(old_page); /* we did a get_page in the beginning */ > + return ret; > +} > + > +/** > + * read_opcode - read the opcode at a given virtual address. > + * @tsk: the probed task. > + * @vaddr: the virtual address to store the opcode. > + * @opcode: location to store the read opcode. > + * > + * For task @tsk, read the opcode at @vaddr and store it in @opcode. > + * Return 0 (success) or a negative errno. Wants to called with mmap_sem held as well, right ? > + */ > +int __weak read_opcode(struct task_struct *tsk, unsigned long vaddr, > + uprobe_opcode_t *opcode) > +{ > + struct vm_area_struct *vma; > + struct page *page; > + void *vaddr_new; > + int ret; > + > + ret = get_user_pages(tsk, tsk->mm, vaddr, 1, 0, 0, &page, &vma); > + if (ret <= 0) > + return -EFAULT; > + ret = -EFAULT; > + > + /* > + * check if the page we are interested is read-only mapped > + * Since we are interested in text pages, Our pages of interest > + * should be mapped read-only. > + */ > + if ((vma->vm_flags & (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)) == > + (VM_READ|VM_EXEC)) > + goto put_out; Same as above > + lock_page(page); > + vaddr_new = kmap_atomic(page, KM_USER0); > + vaddr &= ~PAGE_MASK; > + memcpy(&opcode, vaddr_new + vaddr, uprobe_opcode_sz); > + kunmap_atomic(vaddr_new, KM_USER0); > + unlock_page(page); > + ret = uprobe_opcode_sz; ret = 0 ?? At least, that's what the comment above says. > + > +put_out: > + put_page(page); /* we did a get_page in the beginning */ > + return ret; > +} > + -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/