Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753018Ab1DRMVY (ORCPT ); Mon, 18 Apr 2011 08:21:24 -0400 Received: from bombadil.infradead.org ([18.85.46.34]:59650 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751896Ab1DRMVT convert rfc822-to-8bit (ORCPT ); Mon, 18 Apr 2011 08:21:19 -0400 Subject: Re: [PATCH v3 2.6.39-rc1-tip 4/26] 4: uprobes: Breakground page replacement. From: Peter Zijlstra To: Srikar Dronamraju Cc: Ingo Molnar , Steven Rostedt , Linux-mm , Arnaldo Carvalho de Melo , Linus Torvalds , Andi Kleen , Christoph Hellwig , Jonathan Corbet , Thomas Gleixner , Masami Hiramatsu , Oleg Nesterov , Andrew Morton , SystemTap , Jim Keniston , Roland McGrath , Ananth N Mavinakayanahalli , LKML In-Reply-To: <20110401143318.15455.64841.sendpatchset@localhost6.localdomain6> References: <20110401143223.15455.19844.sendpatchset@localhost6.localdomain6> <20110401143318.15455.64841.sendpatchset@localhost6.localdomain6> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Date: Mon, 18 Apr 2011 14:20:25 +0200 Message-ID: <1303129225.32491.776.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4325 Lines: 147 On Fri, 2011-04-01 at 20:03 +0530, Srikar Dronamraju wrote: > +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; > + > + /* 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; Why not return the actual gup() error? > + ret = -EINVAL; > + > + /* > + * We are interested in text pages only. Our pages of interest > + * should be mapped for read and execute only. We desist from > + * adding probes in write mapped pages since the breakpoints > + * might end up in the file copy. > + */ > + if ((vma->vm_flags & (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)) != > + (VM_READ|VM_EXEC)) > + goto put_out; Note how you return -EINVAL here when we're attempting to poke at the wrong kind of mapping. > + /* 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 */ Why not test this assertion with a VM_BUG_ON() or something. > + 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); The use of KM_foo is obsolete and un-needed. > + 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); > + ret = anon_vma_prepare(vma); > + if (!ret) > + 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 read the opcode. > + * @opcode: location to store the read opcode. > + * > + * Called with tsk->mm->mmap_sem held (for read and with a reference to > + * tsk->mm. > + * > + * For task @tsk, read the opcode at @vaddr and store it in @opcode. > + * Return 0 (success) or a negative errno. > + */ > +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; Again, why not return the gup() error proper? > + ret = -EFAULT; > + > + /* > + * We are interested in text pages only. Our pages of interest > + * should be mapped for read and execute only. We desist from > + * adding probes in write mapped pages since the breakpoints > + * might end up in the file copy. > + */ > + if ((vma->vm_flags & (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)) != > + (VM_READ|VM_EXEC)) > + goto put_out; But now you return -EFAULT if we peek at the wrong kind of mapping, which is inconsistent with the -EINVAL of write_opcode(). > + 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); Again, loose the KM_foo. > + unlock_page(page); > + ret = 0; > + > +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/