Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755628Ab0KCQwx (ORCPT ); Wed, 3 Nov 2010 12:52:53 -0400 Received: from mail-ey0-f174.google.com ([209.85.215.174]:40134 "EHLO mail-ey0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754015Ab0KCQwv (ORCPT ); Wed, 3 Nov 2010 12:52:51 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; b=ak10GleVrpudP+CHksyhpnIwNHaFhjkTL8MsT88PEMbakWFm+pFgcjplq8gVwGNFxy JwJ0iTavVcWqkPiuefdXcvn+GI67DP19f3kEiwBv/3D3MgwZyVJbconKEev5dhk+GBPW yds+gbU7v9mdi8/mm/L7wy1YkEanePKs2BK2Q= Date: Wed, 3 Nov 2010 18:52:56 +0200 From: Sergey Senozhatsky To: Oleg Nesterov Cc: Thomas Gleixner , Andrew Morton , Peter Zijlstra , Ingo Molnar , LKML , Stanislaw Gruszka Subject: [PATCH] posix-cpu-timers: rcu_read_lock/unlock protect find_task_by_vpid call Message-ID: <20101103165256.GD30053@swordfish.minsk.epam.com> References: <20101102135821.GA5964@swordfish.minsk.epam.com> <20101102160223.GC5964@swordfish.minsk.epam.com> <20101102183308.GA17720@redhat.com> <20101103105832.GA30053@swordfish.minsk.epam.com> <20101103124835.GA604@redhat.com> <20101103161059.GA13530@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20101103161059.GA13530@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2746 Lines: 86 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. Thomas Gleixner wrote: | We can remove the tasklist_lock while at it. rcu_read_lock is enough. Patch also replaces thread_group_leader with has_group_leader_pid in accordance to comment by Oleg Nesterov: | ... thread_group_leader() check is not relaible without | tasklist. If we race with de_thread() find_task_by_vpid() can find | the new leader before it updates its ->group_leader. | | perhaps it makes sense to change posix_cpu_timer_create() to use | has_group_leader_pid() instead, just to make this code not look racy | and avoid adding new problems. Signed-off-by: Sergey Senozhatsky --- diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c index 6842eeb..05bb717 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))) { + same_thread_group(p, current) : has_group_leader_pid(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; @@ -404,7 +404,7 @@ int posix_cpu_timer_create(struct k_itimer *new_timer) p = current->group_leader; } else { p = find_task_by_vpid(pid); - if (p && !thread_group_leader(p)) + if (p && !has_group_leader_pid(p)) p = NULL; } } @@ -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/