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rcu: Prohibit starting new grace periods while forcing quiescent states 

Reduce the number and variety of race conditions by prohibiting
the start of a new grace period while force_quiescent_state() is
active. A new fqs_active flag in the rcu_state structure is used
to trace whether or not force_quiescent_state() is active, and
this new flag is tested by rcu_start_gp().  If the CPU that
closed out the last grace period needs another grace period,
this new grace period may be delayed up to one scheduling-clock
tick, but it will eventually get started.

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: <126264655052-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Paul E. McKenney 2010-01-04 15:09:02 -08:00 committed by Ingo Molnar
parent 559569acf9
commit 07079d5357
2 changed files with 19 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

31
kernel/rcutree.c
View File

@ -659,7 +659,7 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
struct rcu_data *rdp = rsp->rda[smp_processor_id()];
struct rcu_node *rnp = rcu_get_root(rsp);
if (!cpu_needs_another_gp(rsp, rdp)) {
if (!cpu_needs_another_gp(rsp, rdp) || rsp->fqs_active) {
if (rnp->completed == rsp->completed) {
spin_unlock_irqrestore(&rnp->lock, flags);
return;
@ -1195,6 +1195,7 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
struct rcu_node *rnp = rcu_get_root(rsp);
u8 signaled;
u8 forcenow;
u8 gpdone;
if (!rcu_gp_in_progress(rsp))
return; /* No grace period in progress, nothing to force. */
@ -1206,15 +1207,16 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
(long)(rsp->jiffies_force_qs - jiffies) >= 0)
goto unlock_fqs_ret; /* no emergency and done recently. */
rsp->n_force_qs++;
spin_lock(&rnp->lock);
spin_lock(&rnp->lock); /* irqs already disabled */
lastcomp = rsp->gpnum - 1;
signaled = rsp->signaled;
rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
if(!rcu_gp_in_progress(rsp)) {
rsp->n_force_qs_ngp++;
spin_unlock(&rnp->lock);
spin_unlock(&rnp->lock); /* irqs remain disabled */
goto unlock_fqs_ret; /* no GP in progress, time updated. */
}
rsp->fqs_active = 1;
switch (signaled) {
case RCU_GP_IDLE:
case RCU_GP_INIT:
@ -1223,15 +1225,16 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
case RCU_SAVE_DYNTICK:
spin_unlock(&rnp->lock);
spin_unlock(&rnp->lock); /* irqs remain disabled */
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_fqs_ret;
spin_lock(&rnp->lock);
gpdone = rcu_process_dyntick(rsp, lastcomp,
dyntick_save_progress_counter);
spin_lock(&rnp->lock); /* irqs already disabled */
if (gpdone)
break;
/* fall into next case. */
case RCU_SAVE_COMPLETED:
@ -1252,17 +1255,17 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
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_fqs_ret;
spin_unlock(&rnp->lock); /* irqs remain disabled */
gpdone = rcu_process_dyntick(rsp, rsp->completed_fqs,
rcu_implicit_dynticks_qs);
/* Leave state in case more forcing is required. */
spin_lock(&rnp->lock);
spin_lock(&rnp->lock); /* irqs already disabled */
break;
}
spin_unlock(&rnp->lock);
rsp->fqs_active = 0;
spin_unlock(&rnp->lock); /* irqs remain disabled */
unlock_fqs_ret:
spin_unlock_irqrestore(&rsp->fqslock, flags);
}

2
kernel/rcutree.h
View File

@ -277,6 +277,8 @@ struct rcu_state {
u8 signaled ____cacheline_internodealigned_in_smp;
/* Force QS state. */
u8 fqs_active; /* force_quiescent_state() */
/* is running. */
long gpnum; /* Current gp number. */
long completed; /* # of last completed gp. */