From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail6.bemta12.messagelabs.com (mail6.bemta12.messagelabs.com [216.82.250.247]) by kanga.kvack.org (Postfix) with ESMTP id 552A09000DF for ; Mon, 3 Oct 2011 12:33:21 -0400 (EDT) Date: Mon, 3 Oct 2011 18:29:05 +0200 From: Oleg Nesterov Subject: Re: [PATCH v5 3.1.0-rc4-tip 5/26] Uprobes: copy of the original instruction. Message-ID: <20111003162905.GA3752@redhat.com> References: <20110920115938.25326.93059.sendpatchset@srdronam.in.ibm.com> <20110920120057.25326.63780.sendpatchset@srdronam.in.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110920120057.25326.63780.sendpatchset@srdronam.in.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Srikar Dronamraju Cc: Peter Zijlstra , Ingo Molnar , Steven Rostedt , Linux-mm , Arnaldo Carvalho de Melo , Linus Torvalds , Masami Hiramatsu , Hugh Dickins , Christoph Hellwig , Ananth N Mavinakayanahalli , Thomas Gleixner , Jonathan Corbet , LKML , Jim Keniston , Roland McGrath , Andi Kleen , Andrew Morton On 09/20, Srikar Dronamraju wrote: > > +static int __copy_insn(struct address_space *mapping, > + struct vm_area_struct *vma, char *insn, > + unsigned long nbytes, unsigned long offset) > +{ > + struct file *filp = vma->vm_file; > + struct page *page; > + void *vaddr; > + unsigned long off1; > + unsigned long idx; > + > + if (!filp) > + return -EINVAL; > + > + idx = (unsigned long) (offset >> PAGE_CACHE_SHIFT); > + off1 = offset &= ~PAGE_MASK; > + > + /* > + * Ensure that the page that has the original instruction is > + * populated and in page-cache. > + */ Hmm. But how we can ensure? > + page_cache_sync_readahead(mapping, &filp->f_ra, filp, idx, 1); This schedules the i/o, > + page = grab_cache_page(mapping, idx); This finds/locks the page in the page-cache, > + if (!page) > + return -ENOMEM; > + > + vaddr = kmap_atomic(page); > + memcpy(insn, vaddr + off1, nbytes); What if this page is not PageUptodate() ? Somehow this assumes that the i/o was already completed, I don't understand this. But I am starting to think I simply do not understand this change. To the point, I do not underestand why do we need copy_insn() at all. We are going to replace this page, can't we save/analyze ->insn later when we copy the content of the old page? Most probably I missed something simple... > +static struct task_struct *get_mm_owner(struct mm_struct *mm) > +{ > + struct task_struct *tsk; > + > + rcu_read_lock(); > + tsk = rcu_dereference(mm->owner); > + if (tsk) > + get_task_struct(tsk); > + rcu_read_unlock(); > + return tsk; > +} Hmm. Do we really need task_struct? > -static int install_breakpoint(struct mm_struct *mm, struct uprobe *uprobe) > +static int install_breakpoint(struct mm_struct *mm, struct uprobe *uprobe, > + struct vm_area_struct *vma, loff_t vaddr) > { > - /* Placeholder: Yet to be implemented */ > + struct task_struct *tsk; > + unsigned long addr; > + int ret = -EINVAL; > + > if (!uprobe->consumers) > return 0; > > - atomic_inc(&mm->mm_uprobes_count); > - return 0; > + tsk = get_mm_owner(mm); > + if (!tsk) /* task is probably exiting; bail-out */ > + return -ESRCH; > + > + if (vaddr > TASK_SIZE_OF(tsk)) > + goto put_return; But this should not be possible, no? How it can map this vaddr above TASK_SIZE ? get_user_pages(tsk => NULL) is fine. Why else do we need mm->owner ? Probably used by the next patches... Say, is_32bit_app(tsk). This can use mm->context.ia32_compat (hopefully will be replaced with MMF_COMPAT). Oleg. -- 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