From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756484Ab2FFOwx (ORCPT ); Wed, 6 Jun 2012 10:52:53 -0400 Received: from mx1.redhat.com ([209.132.183.28]:47912 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756464Ab2FFOww (ORCPT ); Wed, 6 Jun 2012 10:52:52 -0400 Date: Wed, 6 Jun 2012 16:50:26 +0200 From: Oleg Nesterov To: Ingo Molnar , Peter Zijlstra , Srikar Dronamraju Cc: Ananth N Mavinakayanahalli , Anton Arapov , Linus Torvalds , Masami Hiramatsu , linux-kernel@vger.kernel.org Subject: [PATCH v2 3/3] uprobes: document uprobe_register() vs uprobe_mmap() race Message-ID: <20120606145026.GD24078@redhat.com> References: <20120604145238.GA6408@redhat.com> <20120606144933.GA24078@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120606144933.GA24078@redhat.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Peter Zijlstra Because the mind is treacherous and makes us forget we need to write stuff down. Signed-off-by: Peter Zijlstra Signed-off-by: Oleg Nesterov --- kernel/events/uprobes.c | 31 ++++++++++++++++++++++++++++--- 1 files changed, 28 insertions(+), 3 deletions(-) diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c index 88e903d..6e3b181 100644 --- a/kernel/events/uprobes.c +++ b/kernel/events/uprobes.c @@ -44,6 +44,23 @@ static DEFINE_SPINLOCK(uprobes_treelock); /* serialize rbtree access */ #define UPROBES_HASH_SZ 13 +/* + * We need separate register/unregister and mmap/munmap lock hashes because + * of mmap_sem nesting. + * + * uprobe_register() needs to install probes on (potentially) all processes + * and thus needs to acquire multiple mmap_sems (consequtively, not + * concurrently), whereas uprobe_mmap() is called while holding mmap_sem + * for the particular process doing the mmap. + * + * uprobe_register()->register_for_each_vma() needs to drop/acquire mmap_sem + * because of lock order against i_mmap_mutex. This means there's a hole in + * the register vma iteration where a mmap() can happen. + * + * Thus uprobe_register() can race with uprobe_mmap() and we can try and + * install a probe where one is already installed. + */ + /* serialize (un)register */ static struct mutex uprobes_mutex[UPROBES_HASH_SZ]; @@ -353,7 +370,9 @@ out: int __weak set_swbp(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long vaddr) { int result; - + /* + * See the comment near uprobes_hash(). + */ result = is_swbp_at_addr(mm, vaddr); if (result == 1) return -EEXIST; @@ -855,6 +874,10 @@ static int register_for_each_vma(struct uprobe *uprobe, bool is_register) if (is_register) { err = install_breakpoint(uprobe, mm, vma, info->vaddr); + /* + * We can race against uprobe_mmap(), see the + * comment near uprobe_hash(). + */ if (err == -EEXIST) err = 0; } else { @@ -1063,8 +1086,10 @@ int uprobe_mmap(struct vm_area_struct *vma) } ret = install_breakpoint(uprobe, vma->vm_mm, vma, vaddr); - - /* Ignore double add: */ + /* + * We can race against uprobe_register(), see the + * comment near uprobe_hash(). + */ if (ret == -EEXIST) { ret = 0; -- 1.5.5.1