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rcu: Adjust force_quiescent_state() locking, step 1 

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>
This commit is contained in:
Paul E. McKenney 2010-01-04 15:09:00 -08:00 committed by Ingo Molnar
parent 7284ce6c9f
commit f96e9232e0
1 changed files with 18 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

27
kernel/rcutree.c
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@ -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);
}