From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx115.postini.com [74.125.245.115]) by kanga.kvack.org (Postfix) with SMTP id 398576B00EA for ; Thu, 5 Apr 2012 18:22:33 -0400 (EDT) Date: Fri, 6 Apr 2012 00:22:03 +0200 From: Oleg Nesterov Subject: [PATCH 5/6] uprobes: teach handle_swbp() to rely on "is_swbp" rather than uprobes_srcu Message-ID: <20120405222203.GE19166@redhat.com> References: <20120405222024.GA19154@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120405222024.GA19154@redhat.com> Sender: owner-linux-mm@kvack.org List-ID: To: Ingo Molnar , Peter Zijlstra , Srikar Dronamraju Cc: Andrew Morton , Linus Torvalds , Ananth N Mavinakayanahalli , Jim Keniston , LKML , Linux-mm , Andi Kleen , Christoph Hellwig , Steven Rostedt , Arnaldo Carvalho de Melo , Masami Hiramatsu , Thomas Gleixner , Anton Arapov Currently handle_swbp() assumes that it can't race with unregister, so it roughly does: if (find_uprobe(vaddr)) process_uprobe(); else send_sig(SIGTRAP); This relies on the not-really-working uprobes_srcu code we are going to remove. With this patch we rely on the result of is_swbp_at_addr_fast(bp_vaddr) if find_uprobe() fails. If is_swbp == 1, then we hit the normal int3, we should send SIGTRAP. If is_swbp == 0, we raced with uprobe_unregister(), we simply restart this insn again. The "difficult" case is is_swbp == -EFAULT, when we can't read this memory. In this case I think we should restart too, and this is more correct compared to the current code which sends SIGTRAP. Ignoring ENOMEM/etc from get_user_pages(), this can only happen if another thread unmaps this memory before find_active_uprobe() takes mmap_sem. It would be better to pretend it was unmapped before this insn was executed, restart, and get SIGSEGV. --- kernel/events/uprobes.c | 18 +++++++++++++++--- 1 files changed, 15 insertions(+), 3 deletions(-) diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c index 2af458d..ed76ee5 100644 --- a/kernel/events/uprobes.c +++ b/kernel/events/uprobes.c @@ -1538,14 +1538,26 @@ static void handle_swbp(struct pt_regs *regs) struct uprobe_task *utask; struct uprobe *uprobe; unsigned long bp_vaddr; - int is_swbp; + int uninitialized_var(is_swbp); bp_vaddr = uprobe_get_swbp_addr(regs); uprobe = find_active_uprobe(bp_vaddr, &is_swbp); if (!uprobe) { - /* No matching uprobe; signal SIGTRAP. */ - send_sig(SIGTRAP, current, 0); + if (is_swbp > 0) { + /* No matching uprobe; signal SIGTRAP. */ + send_sig(SIGTRAP, current, 0); + } else { + /* + * Either we raced with uprobe_unregister() or we can't + * access this memory. The latter is only possible if + * another thread plays with our ->mm. In both cases + * we can simply restart. If this vma was unmapped we + * can pretend this insn was not executed yet and get + * the (correct) SIGSEGV after restart. + */ + instruction_pointer_set(regs, bp_vaddr); + } return; } -- 1.5.5.1 -- 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