From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753952Ab2DAViS (ORCPT ); Sun, 1 Apr 2012 17:38:18 -0400 Received: from mx1.redhat.com ([209.132.183.28]:24621 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753890Ab2DAViR (ORCPT ); Sun, 1 Apr 2012 17:38:17 -0400 Date: Sun, 1 Apr 2012 23:38:04 +0200 From: Oleg Nesterov To: Steven Rostedt Cc: Ingo Molnar , Jason Baron , linux-kernel@vger.kernel.org, Hendrik Brueckner , Frederic Weisbecker Subject: [PATCH 1/2] tracing: syscall_*regfunc() can race with copy_process() Message-ID: <20120401213804.GB17795@redhat.com> References: <20120330183104.GA12927@redhat.com> <1333134131.23924.191.camel@gandalf.stny.rr.com> <20120330201550.GA16628@redhat.com> <1333152806.23924.196.camel@gandalf.stny.rr.com> <20120331204501.GA18572@redhat.com> <1333229859.23924.200.camel@gandalf.stny.rr.com> <20120401213748.GA17795@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120401213748.GA17795@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 syscall_regfunc() and syscall_unregfunc() should set/clear TIF_SYSCALL_TRACEPOINT system-wide, but do_each_thread() can race with copy_process() and miss the new child which was not added to init_task.tasks list yet. Change copy_process() to update the child's TIF_SYSCALL_TRACEPOINT under tasklist. While at it, - remove _irqsafe from syscall_regfunc/syscall_unregfunc, read_lock(tasklist) doesn't need to disable irqs. - change syscall_unregfunc() to check PF_KTHREAD to skip the kernel threads, ->mm != NULL is the common mistake. Note: probably this check should be simply removed, needs another patch. Signed-off-by: Oleg Nesterov --- kernel/fork.c | 7 +++++++ kernel/tracepoint.c | 12 +++++------- 2 files changed, 12 insertions(+), 7 deletions(-) diff --git a/kernel/fork.c b/kernel/fork.c index 34d7ed1..772d4a5 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1446,7 +1446,14 @@ static struct task_struct *copy_process(unsigned long clone_flags, total_forks++; spin_unlock(¤t->sighand->siglock); +#ifdef CONFIG_TRACEPOINTS + if (test_thread_flag(TIF_SYSCALL_TRACEPOINT)) + set_tsk_thread_flag(p, TIF_SYSCALL_TRACEPOINT); + else + clear_tsk_thread_flag(p, TIF_SYSCALL_TRACEPOINT); +#endif write_unlock_irq(&tasklist_lock); + proc_fork_connector(p); cgroup_post_fork(p); if (clone_flags & CLONE_THREAD) diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c index f1539de..e2a4523 100644 --- a/kernel/tracepoint.c +++ b/kernel/tracepoint.c @@ -734,33 +734,31 @@ static int sys_tracepoint_refcount; void syscall_regfunc(void) { - unsigned long flags; struct task_struct *g, *t; if (!sys_tracepoint_refcount) { - read_lock_irqsave(&tasklist_lock, flags); + read_lock(&tasklist_lock); do_each_thread(g, t) { /* Skip kernel threads. */ - if (t->mm) + if (!(t->flags & PF_KTHREAD)) set_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT); } while_each_thread(g, t); - read_unlock_irqrestore(&tasklist_lock, flags); + read_unlock(&tasklist_lock); } sys_tracepoint_refcount++; } void syscall_unregfunc(void) { - unsigned long flags; struct task_struct *g, *t; sys_tracepoint_refcount--; if (!sys_tracepoint_refcount) { - read_lock_irqsave(&tasklist_lock, flags); + read_lock(&tasklist_lock); do_each_thread(g, t) { clear_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT); } while_each_thread(g, t); - read_unlock_irqrestore(&tasklist_lock, flags); + read_unlock(&tasklist_lock); } } #endif -- 1.5.5.1