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Subject[PATCH RFC tip/core/rcu 01/18] rcu: adjust force_quiescent_state() locking, step 1
Date
Not yet for inclusion, proposing for 2.6.34.

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>
---
kernel/rcutree.c | 27 ++++++++++++++++++---------
1 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 53ae959..eae331d 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -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);
}

--
1.5.2.5


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