From de078d875cc7fc709f7818f26d38389c04369826 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 8 Sep 2009 15:54:36 -0700 Subject: [PATCH] rcu: Need to update rnp->gpnum if preemptable RCU is to be reliable 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 Acked-by: Steven Rostedt Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: akpm@linux-foundation.org Cc: mathieu.desnoyers@polymtl.ca Cc: josht@linux.vnet.ibm.com Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org LKML-Reference: <12524504771622-git-send-email-> Signed-off-by: Ingo Molnar --- kernel/rcutree.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 6b11b07cfe7f..c634a92d1217 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -632,6 +632,7 @@ 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; @@ -657,8 +658,10 @@ 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, @@ -679,6 +682,7 @@ 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. */ } -- 2.30.2