From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753038Ab2FRIzt (ORCPT ); Mon, 18 Jun 2012 04:55:49 -0400 Received: from terminus.zytor.com ([198.137.202.10]:40495 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751958Ab2FRIzr (ORCPT ); Mon, 18 Jun 2012 04:55:47 -0400 Date: Mon, 18 Jun 2012 01:55:19 -0700 From: tip-bot for Peter Zijlstra Message-ID: Cc: linux-kernel@vger.kernel.org, hpa@zytor.com, mingo@kernel.org, a.p.zijlstra@chello.nl, peterz@infradead.org, ananth@in.ibm.com, anton@redhat.com, srikar@linux.vnet.ibm.com, tglx@linutronix.de, oleg@redhat.com Reply-To: mingo@kernel.org, hpa@zytor.com, linux-kernel@vger.kernel.org, a.p.zijlstra@chello.nl, peterz@infradead.org, ananth@in.ibm.com, anton@redhat.com, srikar@linux.vnet.ibm.com, oleg@redhat.com, tglx@linutronix.de In-Reply-To: <20120615154339.GA9591@redhat.com> References: <20120615154339.GA9591@redhat.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:perf/core] uprobes: Document uprobe_register() vs uprobe_mmap () race Git-Commit-ID: c5784de2b351fe871bb57487878f7fc7ec5b075c X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.6 (terminus.zytor.com [127.0.0.1]); Mon, 18 Jun 2012 01:55:26 -0700 (PDT) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: c5784de2b351fe871bb57487878f7fc7ec5b075c Gitweb: http://git.kernel.org/tip/c5784de2b351fe871bb57487878f7fc7ec5b075c Author: Peter Zijlstra AuthorDate: Fri, 15 Jun 2012 17:43:39 +0200 Committer: Ingo Molnar CommitDate: Sat, 16 Jun 2012 09:10:45 +0200 uprobes: Document uprobe_register() vs uprobe_mmap() race 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 Cc: Ananth N Mavinakayanahalli Cc: Anton Arapov Cc: Peter Zijlstra Cc: Srikar Dronamraju Link: http://lkml.kernel.org/r/20120615154339.GA9591@redhat.com Signed-off-by: Ingo Molnar --- 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 897417d..2671d9a 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]; @@ -339,7 +356,9 @@ 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; @@ -845,6 +864,10 @@ 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 { @@ -1054,8 +1077,10 @@ 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;