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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2010-01-04 18:09:08 -0500
committerIngo Molnar <mingo@elte.hu>2010-01-13 03:06:04 -0500
commit45f014c52eef022873b19d6a20eb0ec9668f2b09 (patch)
tree036e3987276a5e689869a47b3641d70588db2489 /kernel/rcutree.c
parentee47eb9f4da6f44af965d6d049e77ee8c8a4b822 (diff)
rcu: Remove redundant grace-period check
The rcu_process_dyntick() function checks twice for the end of the current grace period. However, it holds the current rcu_node structure's ->lock field throughout, and doesn't get to the second call to rcu_gp_in_progress() unless there is at least one CPU corresponding to this rcu_node structure that has not yet checked in for the current grace period, which would prevent the current grace period from ending. So the current grace period cannot have ended, and the second check is redundant, so remove it. Also, given that this function is used even with !CONFIG_NO_HZ, its name is quite misleading. Change from rcu_process_dyntick() to force_qs_rnp(). 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: <1262646550562-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/rcutree.c')
-rw-r--r--kernel/rcutree.c9
1 files changed, 4 insertions, 5 deletions
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 6268f37adfc4..d9202857d3ad 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1146,8 +1146,7 @@ void rcu_check_callbacks(int cpu, int user)
1146 * have not yet encountered a quiescent state, using the function specified. 1146 * have not yet encountered a quiescent state, using the function specified.
1147 * The caller must have suppressed start of new grace periods. 1147 * The caller must have suppressed start of new grace periods.
1148 */ 1148 */
1149static void rcu_process_dyntick(struct rcu_state *rsp, 1149static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *))
1150 int (*f)(struct rcu_data *))
1151{ 1150{
1152 unsigned long bit; 1151 unsigned long bit;
1153 int cpu; 1152 int cpu;
@@ -1172,7 +1171,7 @@ static void rcu_process_dyntick(struct rcu_state *rsp,
1172 if ((rnp->qsmask & bit) != 0 && f(rsp->rda[cpu])) 1171 if ((rnp->qsmask & bit) != 0 && f(rsp->rda[cpu]))
1173 mask |= bit; 1172 mask |= bit;
1174 } 1173 }
1175 if (mask != 0 && rcu_gp_in_progress(rsp)) { 1174 if (mask != 0) {
1176 1175
1177 /* rcu_report_qs_rnp() releases rnp->lock. */ 1176 /* rcu_report_qs_rnp() releases rnp->lock. */
1178 rcu_report_qs_rnp(mask, rsp, rnp, flags); 1177 rcu_report_qs_rnp(mask, rsp, rnp, flags);
@@ -1222,7 +1221,7 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
1222 break; /* So gcc recognizes the dead code. */ 1221 break; /* So gcc recognizes the dead code. */
1223 1222
1224 /* Record dyntick-idle state. */ 1223 /* Record dyntick-idle state. */
1225 rcu_process_dyntick(rsp, dyntick_save_progress_counter); 1224 force_qs_rnp(rsp, dyntick_save_progress_counter);
1226 spin_lock(&rnp->lock); /* irqs already disabled */ 1225 spin_lock(&rnp->lock); /* irqs already disabled */
1227 if (rcu_gp_in_progress(rsp)) 1226 if (rcu_gp_in_progress(rsp))
1228 rsp->signaled = RCU_FORCE_QS; 1227 rsp->signaled = RCU_FORCE_QS;
@@ -1232,7 +1231,7 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
1232 1231
1233 /* Check dyntick-idle state, send IPI to laggarts. */ 1232 /* Check dyntick-idle state, send IPI to laggarts. */
1234 spin_unlock(&rnp->lock); /* irqs remain disabled */ 1233 spin_unlock(&rnp->lock); /* irqs remain disabled */
1235 rcu_process_dyntick(rsp, rcu_implicit_dynticks_qs); 1234 force_qs_rnp(rsp, rcu_implicit_dynticks_qs);
1236 1235
1237 /* Leave state in case more forcing is required. */ 1236 /* Leave state in case more forcing is required. */
1238 1237