From mboxrd@z Thu Jan 1 00:00:00 1970 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752608AbZIHWyh (ORCPT ); Tue, 8 Sep 2009 18:54:37 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752549AbZIHWyg (ORCPT ); Tue, 8 Sep 2009 18:54:36 -0400 Received: from e2.ny.us.ibm.com ([32.97.182.142]:37395 "EHLO e2.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751822AbZIHWyg (ORCPT ); Tue, 8 Sep 2009 18:54:36 -0400 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, josht@linux.vnet.ibm.com, dvhltc@us.ibm.com, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 2/3] Need to update rnp->gpnum if preemptable RCU is to be reliable. Date: Tue, 8 Sep 2009 15:54:36 -0700 Message-Id: <12524504771622-git-send-email-> X-Mailer: git-send-email 1.5.2.5 In-Reply-To: <20090908225349.GA19524@linux.vnet.ibm.com> References: <20090908225349.GA19524@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Paul E. McKenney Without this patch, tasks preempted in RCU read-side critical sections can fail to block the grace period, given that rnp->gpnum is used to determine which rnp->blocked_tasks[] element the preempted task is enqueued on. Before the patch, rnp->gpnum is always zero, so preempted tasks are always enqueued on rnp->blocked_tasks[0], which is correct only when the current CPU has not checked into the current grace period and the grace-period number is even, or, similarly, if the current CPU -has- checked into the current grace period and the grace-period number is odd. Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 6 +++++- 1 files changed, 5 insertions(+), 1 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 71bc797..03866bd 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -627,6 +627,7 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags) /* Special-case the common single-level case. */ if (NUM_RCU_NODES == 1) { rnp->qsmask = rnp->qsmaskinit; + rnp->gpnum = rsp->gpnum; rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state OK. */ spin_unlock_irqrestore(&rnp->lock, flags); return; @@ -652,8 +653,10 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags) */ rnp_end = rsp->level[NUM_RCU_LVLS - 1]; - for (rnp_cur = &rsp->node[0]; rnp_cur < rnp_end; rnp_cur++) + for (rnp_cur = &rsp->node[0]; rnp_cur < rnp_end; rnp_cur++) { rnp_cur->qsmask = rnp_cur->qsmaskinit; + rnp->gpnum = rsp->gpnum; + } /* * Now set up the leaf nodes. Here we must be careful. First, @@ -674,6 +677,7 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags) for (; rnp_cur < rnp_end; rnp_cur++) { spin_lock(&rnp_cur->lock); /* irqs already disabled. */ rnp_cur->qsmask = rnp_cur->qsmaskinit; + rnp->gpnum = rsp->gpnum; spin_unlock(&rnp_cur->lock); /* irqs already disabled. */ } -- 1.5.2.5