From: Paul E. McKenney Date: Fri, 25 Jan 2008 20:08:24 +0000 (+0100) Subject: Preempt-RCU: fix rcu_barrier for preemptive environment. X-Git-Tag: v2.6.25-rc1~1237^2~36 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e0ecfa7917cafe72f4a75f87e8bb5d8d51dc534f;p=linux-2.6 Preempt-RCU: fix rcu_barrier for preemptive environment. Fix rcu_barrier() to work properly in preemptive kernel environment. Also, the ordering of callback must be preserved while moving callbacks to another CPU during CPU hotplug. Signed-off-by: Gautham R Shenoy Signed-off-by: Dipankar Sarma Signed-off-by: Paul E. McKenney Reviewed-by: Steven Rostedt Signed-off-by: Ingo Molnar --- diff --git a/kernel/rcuclassic.c b/kernel/rcuclassic.c index 18369e3386..ce0cf16cab 100644 --- a/kernel/rcuclassic.c +++ b/kernel/rcuclassic.c @@ -371,9 +371,9 @@ static void __rcu_offline_cpu(struct rcu_data *this_rdp, if (rcp->cur != rcp->completed) cpu_quiet(rdp->cpu, rcp); spin_unlock_bh(&rcp->lock); + rcu_move_batch(this_rdp, rdp->donelist, rdp->donetail); rcu_move_batch(this_rdp, rdp->curlist, rdp->curtail); rcu_move_batch(this_rdp, rdp->nxtlist, rdp->nxttail); - rcu_move_batch(this_rdp, rdp->donelist, rdp->donetail); } static void rcu_offline_cpu(int cpu) diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c index 0ccd0095eb..760dfc233a 100644 --- a/kernel/rcupdate.c +++ b/kernel/rcupdate.c @@ -115,7 +115,17 @@ void rcu_barrier(void) mutex_lock(&rcu_barrier_mutex); init_completion(&rcu_barrier_completion); atomic_set(&rcu_barrier_cpu_count, 0); + /* + * The queueing of callbacks in all CPUs must be atomic with + * respect to RCU, otherwise one CPU may queue a callback, + * wait for a grace period, decrement barrier count and call + * complete(), while other CPUs have not yet queued anything. + * So, we need to make sure that grace periods cannot complete + * until all the callbacks are queued. + */ + rcu_read_lock(); on_each_cpu(rcu_barrier_func, NULL, 0, 1); + rcu_read_unlock(); wait_for_completion(&rcu_barrier_completion); mutex_unlock(&rcu_barrier_mutex); }