From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751184AbWFUGHE (ORCPT ); Wed, 21 Jun 2006 02:07:04 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751187AbWFUGHE (ORCPT ); Wed, 21 Jun 2006 02:07:04 -0400 Received: from ausmtp06.au.ibm.com ([202.81.18.155]:62630 "EHLO ausmtp06.au.ibm.com") by vger.kernel.org with ESMTP id S1751184AbWFUGHB (ORCPT ); Wed, 21 Jun 2006 02:07:01 -0400 From: Balbir Singh To: akpm@osdl.org Cc: Shailabh.Nagar@d23av01.au.ibm.com (nagar@watson.ibm.com), Balbir Singh , Jay.Lan@d23av01.au.ibm.com (jlan@engr.sgi.com), linux-kernel@vger.kernel.org Date: Wed, 21 Jun 2006 11:29:52 +0530 Message-Id: <20060621055952.6658.49704.sendpatchset@localhost.localdomain> Subject: [PATCH 2.6.17-rc6-mm2] Fix exit race in per-task-delay-accounting Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hi, Andrew, This patch fixes a race in per-task-delay-accounting. This race was reported by Jay Lan. I tested the patch using cerebrus test control system for eight hours with getdelays running on the side (for both push and pull of delay statistics). It fixed the problem that Jay Lan saw. Here's an explanation of the race condition Consider tasks of the same thread group exiting, lets call them T1 and T2 T1 T2 CPU0 CPU1 ===== ===== do_exit() ... do_exit() taskstats_exit_send() ... taskstats_exit_send() fill_tgid() delayacct_add_tsk() delayacct_tsk_exit() .... __delayacct_add_tsk() While T1 is yet to be removed from the thread group. T1->delays is set to NULL between delayacct_add_tsk() and __delayacct_add_tsk() call. When T2 looks for threads in the thread group, it finds T1 and tries to collect stats for it. When we get to the spin_lock() in __delayacct_add_tsk(), we find T1->delays is a NULL pointer. Signed-off-by: Balbir Singh --- include/linux/taskstats_kern.h | 1 + kernel/delayacct.c | 5 ++++- kernel/taskstats.c | 5 ++++- 3 files changed, 9 insertions(+), 2 deletions(-) diff -puN kernel/taskstats.c~per-task-delay-accounting-fix-exit-race kernel/taskstats.c --- linux-2.6.17-rc6/kernel/taskstats.c~per-task-delay-accounting-fix-exit-race 2006-06-20 13:49:29.000000000 +0530 +++ linux-2.6.17-rc6-balbir/kernel/taskstats.c 2006-06-20 13:49:29.000000000 +0530 @@ -25,7 +25,7 @@ static DEFINE_PER_CPU(__u32, taskstats_seqnum) = { 0 }; static int family_registered = 0; kmem_cache_t *taskstats_cache; -static DEFINE_MUTEX(taskstats_exit_mutex); +DEFINE_MUTEX(taskstats_exit_mutex); static struct genl_family family = { .id = GENL_ID_GENERATE, @@ -193,6 +193,7 @@ static int taskstats_send_stats(struct s if (rc < 0) return rc; + mutex_lock(&taskstats_exit_mutex); if (info->attrs[TASKSTATS_CMD_ATTR_PID]) { u32 pid = nla_get_u32(info->attrs[TASKSTATS_CMD_ATTR_PID]); rc = fill_pid(pid, NULL, &stats); @@ -218,6 +219,7 @@ static int taskstats_send_stats(struct s goto err; } + mutex_unlock(&taskstats_exit_mutex); nla_nest_end(rep_skb, na); return send_reply(rep_skb, info->snd_pid, TASKSTATS_MSG_UNICAST); @@ -226,6 +228,7 @@ nla_put_failure: return genlmsg_cancel(rep_skb, reply); err: nlmsg_free(rep_skb); + mutex_unlock(&taskstats_exit_mutex); return rc; } diff -puN kernel/delayacct.c~per-task-delay-accounting-fix-exit-race kernel/delayacct.c --- linux-2.6.17-rc6/kernel/delayacct.c~per-task-delay-accounting-fix-exit-race 2006-06-20 13:49:29.000000000 +0530 +++ linux-2.6.17-rc6-balbir/kernel/delayacct.c 2006-06-20 13:49:29.000000000 +0530 @@ -48,8 +48,11 @@ void __delayacct_tsk_init(struct task_st void __delayacct_tsk_exit(struct task_struct *tsk) { - kmem_cache_free(delayacct_cache, tsk->delays); + struct task_delay_info *delays = tsk->delays; + mutex_lock(&taskstats_exit_mutex); tsk->delays = NULL; + mutex_unlock(&taskstats_exit_mutex); + kmem_cache_free(delayacct_cache, delays); } /* diff -puN include/linux/taskstats_kern.h~per-task-delay-accounting-fix-exit-race include/linux/taskstats_kern.h --- linux-2.6.17-rc6/include/linux/taskstats_kern.h~per-task-delay-accounting-fix-exit-race 2006-06-20 13:49:29.000000000 +0530 +++ linux-2.6.17-rc6-balbir/include/linux/taskstats_kern.h 2006-06-20 13:49:29.000000000 +0530 @@ -17,6 +17,7 @@ enum { #ifdef CONFIG_TASKSTATS extern kmem_cache_t *taskstats_cache; +extern struct mutex taskstats_exit_mutex; static inline void taskstats_exit_alloc(struct taskstats **ptidstats, struct taskstats **ptgidstats) _ -- Balbir Singh, Linux Technology Center, IBM Software Labs