Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753796Ab0KHQBt (ORCPT ); Mon, 8 Nov 2010 11:01:49 -0500 Received: from caiajhbdcbef.dreamhost.com ([208.97.132.145]:47103 "EHLO homiemail-a2.g.dreamhost.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753022Ab0KHQBs (ORCPT ); Mon, 8 Nov 2010 11:01:48 -0500 Subject: Re: [PATCH] rcu_read_lock/unlock protect find_task_by_vpid call From: Davidlohr Bueso Reply-To: dave@gnu.org To: Sergey Senozhatsky , "Paul E. McKenney" Cc: Alexander Viro , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Andrew Morton , Ingo Molnar In-Reply-To: <20101029125550.GA3932@swordfish.minsk.epam.com> References: <20101029125550.GA3932@swordfish.minsk.epam.com> Content-Type: text/plain; charset="UTF-8" Date: Mon, 08 Nov 2010 13:01:35 -0300 Message-ID: <1289232095.2206.5.camel@cowboy> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2961 Lines: 101 On Fri, 2010-10-29 at 15:55 +0300, Sergey Senozhatsky wrote: > Commit 4221a9918e38b7494cee341dda7b7b4bb8c04bde "Add RCU check for > find_task_by_vpid()" introduced rcu_lockdep_assert to find_task_by_pid_ns. > Assertion failed in sys_ioprio_get. The patch is fixing assertion > failure in ioprio_set as well. > > =================================================== > [ INFO: suspicious rcu_dereference_check() usage. ] > --------------------------------------------------- > kernel/pid.c:419 invoked rcu_dereference_check() without protection! > > rcu_scheduler_active = 1, debug_locks = 0 > 1 lock held by iotop/4254: > #0: (tasklist_lock){.?.?..}, at: [] sys_ioprio_get+0x22/0x2da > > stack backtrace: > Pid: 4254, comm: iotop Not tainted > Call Trace: > [] lockdep_rcu_dereference+0xaa/0xb2 > [] find_task_by_pid_ns+0x4f/0x68 > [] find_task_by_vpid+0x1d/0x1f > [] sys_ioprio_get+0x50/0x2da > [] system_call_fastpath+0x16/0x1b > > > Signed-off-by: Sergey Senozhatsky > > --- > > diff --git a/fs/ioprio.c b/fs/ioprio.c > index 748cfb9..666343d 100644 > --- a/fs/ioprio.c > +++ b/fs/ioprio.c > @@ -113,8 +113,11 @@ SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio) > case IOPRIO_WHO_PROCESS: > if (!who) > p = current; > - else > + else { > + rcu_read_lock(); > p = find_task_by_vpid(who); > + rcu_read_unlock(); > + } > if (p) > ret = set_task_ioprio(p, ioprio); > break; > @@ -202,8 +205,11 @@ SYSCALL_DEFINE2(ioprio_get, int, which, int, who) > case IOPRIO_WHO_PROCESS: > if (!who) > p = current; > - else > + else { > + rcu_read_lock(); > p = find_task_by_vpid(who); > + rcu_read_unlock(); > + } > if (p) > ret = get_task_ioprio(p); > break; If you add the rcu_read_lock/unlock() sections, we would also need to update the comment above accordingly. Thanks, Davidlohr From: Davidlohr Bueso Subject: [PATCH] ioprio: remove comment to not use RCU Signed-off-by: Davidlohr Bueso --- fs/ioprio.c | 5 ----- 1 files changed, 0 insertions(+), 5 deletions(-) diff --git a/fs/ioprio.c b/fs/ioprio.c index 748cfb9..72d71de 100644 --- a/fs/ioprio.c +++ b/fs/ioprio.c @@ -103,11 +103,6 @@ SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio) } ret = -ESRCH; - /* - * We want IOPRIO_WHO_PGRP/IOPRIO_WHO_USER to be "atomic", - * so we can't use rcu_read_lock(). See re-copy of ->ioprio - * in copy_process(). - */ read_lock(&tasklist_lock); switch (which) { case IOPRIO_WHO_PROCESS: -- 1.7.1 -- 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/