Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754016Ab0KBQFV (ORCPT ); Tue, 2 Nov 2010 12:05:21 -0400 Received: from www.tglx.de ([62.245.132.106]:40862 "EHLO www.tglx.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752701Ab0KBQFN (ORCPT ); Tue, 2 Nov 2010 12:05:13 -0400 Date: Tue, 2 Nov 2010 17:04:33 +0100 (CET) From: Thomas Gleixner To: Sergey Senozhatsky cc: Andrew Morton , Peter Zijlstra , Ingo Molnar , LKML , Oleg Nesterov Subject: Re: [PATCH] posix-cpu-timers: rcu_read_lock/unlock protect find_task_by_vpid call In-Reply-To: <20101102160223.GC5964@swordfish.minsk.epam.com> Message-ID: References: <20101102135821.GA5964@swordfish.minsk.epam.com> <20101102160223.GC5964@swordfish.minsk.epam.com> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2249 Lines: 73 Just added Oleg to the cc-list On Tue, 2 Nov 2010, Sergey Senozhatsky wrote: > On (11/02/10 16:31), Thomas Gleixner wrote: > > On Tue, 2 Nov 2010, Sergey Senozhatsky wrote: > > > > > Commit 4221a9918e38b7494cee341dda7b7b4bb8c04bde "Add RCU check for > > > find_task_by_vpid()" introduced rcu_lockdep_assert to find_task_by_pid_ns. > > > Add rcu_read_lock/rcu_read_unlock to call find_task_by_vpid. > > > > > > Tetsuo Handa wrote: > > > > > > Quoting from one of posts in that thead > > > http://kerneltrap.org/mailarchive/linux-kernel/2010/2/8/4536388 > > > > > > | Usually tasklist gives enough protection, but if copy_process() fails > > > | it calls free_pid() lockless and does call_rcu(delayed_put_pid(). > > > | This means, without rcu lock find_pid_ns() can't scan the hash table > > > | safely. > > > > We can remove the tasklist_lock while at it. rcu_read_lock is enough. > > > > Please kindly review. > > --- > > diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c > index 6842eeb..96fe2a3 100644 > --- a/kernel/posix-cpu-timers.c > +++ b/kernel/posix-cpu-timers.c > @@ -37,13 +37,13 @@ static int check_clock(const clockid_t which_clock) > if (pid == 0) > return 0; > > - read_lock(&tasklist_lock); > + rcu_read_lock(); > p = find_task_by_vpid(pid); > if (!p || !(CPUCLOCK_PERTHREAD(which_clock) ? > same_thread_group(p, current) : thread_group_leader(p))) { > error = -EINVAL; > } > - read_unlock(&tasklist_lock); > + rcu_read_unlock(); > > return error; > } > @@ -390,7 +390,7 @@ int posix_cpu_timer_create(struct k_itimer *new_timer) > > INIT_LIST_HEAD(&new_timer->it.cpu.entry); > > - read_lock(&tasklist_lock); > + rcu_read_lock(); > if (CPUCLOCK_PERTHREAD(new_timer->it_clock)) { > if (pid == 0) { > p = current; > @@ -414,7 +414,7 @@ int posix_cpu_timer_create(struct k_itimer *new_timer) > } else { > ret = -EINVAL; > } > - read_unlock(&tasklist_lock); > + rcu_read_unlock(); > > 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/