rcu: Adjust force_quiescent_state() locking, step 1
Paul E. McKenney [Mon, 4 Jan 2010 23:09:00 +0000 (15:09 -0800)]
This causes rnp->lock to be held on entry to
force_quiescent_state()'s switch statement.  This is a first
step towards prohibiting starting grace periods while
force_quiescent_state() is executing, which will reduce the
number and complexity of races that force_quiescent_state() is
involved in.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <12626465501455-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/rcutree.c

index 53ae959..eae331d 100644 (file)
@@ -1204,7 +1204,7 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
        }
        if (relaxed &&
            (long)(rsp->jiffies_force_qs - jiffies) >= 0)
-               goto unlock_ret; /* no emergency and done recently. */
+               goto unlock_fqs_ret; /* no emergency and done recently. */
        rsp->n_force_qs++;
        spin_lock(&rnp->lock);
        lastcomp = rsp->gpnum - 1;
@@ -1213,31 +1213,32 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
        if(!rcu_gp_in_progress(rsp)) {
                rsp->n_force_qs_ngp++;
                spin_unlock(&rnp->lock);
-               goto unlock_ret;  /* no GP in progress, time updated. */
+               goto unlock_fqs_ret;  /* no GP in progress, time updated. */
        }
-       spin_unlock(&rnp->lock);
        switch (signaled) {
        case RCU_GP_IDLE:
        case RCU_GP_INIT:
 
+               spin_unlock(&rnp->lock);
                break; /* grace period idle or initializing, ignore. */
 
        case RCU_SAVE_DYNTICK:
 
+               spin_unlock(&rnp->lock);
                if (RCU_SIGNAL_INIT != RCU_SAVE_DYNTICK)
                        break; /* So gcc recognizes the dead code. */
 
                /* Record dyntick-idle state. */
                if (rcu_process_dyntick(rsp, lastcomp,
                                        dyntick_save_progress_counter))
-                       goto unlock_ret;
+                       goto unlock_fqs_ret;
+               spin_lock(&rnp->lock);
                /* fall into next case. */
 
        case RCU_SAVE_COMPLETED:
 
                /* Update state, record completion counter. */
                forcenow = 0;
-               spin_lock(&rnp->lock);
                if (lastcomp + 1 == rsp->gpnum &&
                    lastcomp == rsp->completed &&
                    rsp->signaled == signaled) {
@@ -1245,23 +1246,31 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
                        rsp->completed_fqs = lastcomp;
                        forcenow = signaled == RCU_SAVE_COMPLETED;
                }
-               spin_unlock(&rnp->lock);
-               if (!forcenow)
+               if (!forcenow) {
+                       spin_unlock(&rnp->lock);
                        break;
+               }
                /* fall into next case. */
 
        case RCU_FORCE_QS:
 
                /* Check dyntick-idle state, send IPI to laggarts. */
+               spin_unlock(&rnp->lock);
                if (rcu_process_dyntick(rsp, rsp->completed_fqs,
                                        rcu_implicit_dynticks_qs))
-                       goto unlock_ret;
+                       goto unlock_fqs_ret;
 
                /* Leave state in case more forcing is required. */
 
                break;
+
+       default:
+
+               spin_unlock(&rnp->lock);
+               WARN_ON_ONCE(1);
+               break;
        }
-unlock_ret:
+unlock_fqs_ret:
        spin_unlock_irqrestore(&rsp->fqslock, flags);
 }