Commit d9a3da06 authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Ingo Molnar

rcu: Add expedited grace-period support for preemptible RCU

Implement an synchronize_rcu_expedited() for preemptible RCU
that actually is expedited.  This uses
synchronize_sched_expedited() to force all threads currently
running in a preemptible-RCU read-side critical section onto the
appropriate ->blocked_tasks[] list, then takes a snapshot of all
of these lists and waits for them to drain.
Signed-off-by: default avatarPaul 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: <1259784616158-git-send-email->
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent cf244dc0
...@@ -327,6 +327,11 @@ rcu_torture_cb(struct rcu_head *p) ...@@ -327,6 +327,11 @@ rcu_torture_cb(struct rcu_head *p)
cur_ops->deferred_free(rp); cur_ops->deferred_free(rp);
} }
static int rcu_no_completed(void)
{
return 0;
}
static void rcu_torture_deferred_free(struct rcu_torture *p) static void rcu_torture_deferred_free(struct rcu_torture *p)
{ {
call_rcu(&p->rtort_rcu, rcu_torture_cb); call_rcu(&p->rtort_rcu, rcu_torture_cb);
...@@ -388,6 +393,21 @@ static struct rcu_torture_ops rcu_sync_ops = { ...@@ -388,6 +393,21 @@ static struct rcu_torture_ops rcu_sync_ops = {
.name = "rcu_sync" .name = "rcu_sync"
}; };
static struct rcu_torture_ops rcu_expedited_ops = {
.init = rcu_sync_torture_init,
.cleanup = NULL,
.readlock = rcu_torture_read_lock,
.read_delay = rcu_read_delay, /* just reuse rcu's version. */
.readunlock = rcu_torture_read_unlock,
.completed = rcu_no_completed,
.deferred_free = rcu_sync_torture_deferred_free,
.sync = synchronize_rcu_expedited,
.cb_barrier = NULL,
.stats = NULL,
.irq_capable = 1,
.name = "rcu_expedited"
};
/* /*
* Definitions for rcu_bh torture testing. * Definitions for rcu_bh torture testing.
*/ */
...@@ -581,11 +601,6 @@ static void sched_torture_read_unlock(int idx) ...@@ -581,11 +601,6 @@ static void sched_torture_read_unlock(int idx)
preempt_enable(); preempt_enable();
} }
static int sched_torture_completed(void)
{
return 0;
}
static void rcu_sched_torture_deferred_free(struct rcu_torture *p) static void rcu_sched_torture_deferred_free(struct rcu_torture *p)
{ {
call_rcu_sched(&p->rtort_rcu, rcu_torture_cb); call_rcu_sched(&p->rtort_rcu, rcu_torture_cb);
...@@ -602,7 +617,7 @@ static struct rcu_torture_ops sched_ops = { ...@@ -602,7 +617,7 @@ static struct rcu_torture_ops sched_ops = {
.readlock = sched_torture_read_lock, .readlock = sched_torture_read_lock,
.read_delay = rcu_read_delay, /* just reuse rcu's version. */ .read_delay = rcu_read_delay, /* just reuse rcu's version. */
.readunlock = sched_torture_read_unlock, .readunlock = sched_torture_read_unlock,
.completed = sched_torture_completed, .completed = rcu_no_completed,
.deferred_free = rcu_sched_torture_deferred_free, .deferred_free = rcu_sched_torture_deferred_free,
.sync = sched_torture_synchronize, .sync = sched_torture_synchronize,
.cb_barrier = rcu_barrier_sched, .cb_barrier = rcu_barrier_sched,
...@@ -617,7 +632,7 @@ static struct rcu_torture_ops sched_sync_ops = { ...@@ -617,7 +632,7 @@ static struct rcu_torture_ops sched_sync_ops = {
.readlock = sched_torture_read_lock, .readlock = sched_torture_read_lock,
.read_delay = rcu_read_delay, /* just reuse rcu's version. */ .read_delay = rcu_read_delay, /* just reuse rcu's version. */
.readunlock = sched_torture_read_unlock, .readunlock = sched_torture_read_unlock,
.completed = sched_torture_completed, .completed = rcu_no_completed,
.deferred_free = rcu_sync_torture_deferred_free, .deferred_free = rcu_sync_torture_deferred_free,
.sync = sched_torture_synchronize, .sync = sched_torture_synchronize,
.cb_barrier = NULL, .cb_barrier = NULL,
...@@ -631,7 +646,7 @@ static struct rcu_torture_ops sched_expedited_ops = { ...@@ -631,7 +646,7 @@ static struct rcu_torture_ops sched_expedited_ops = {
.readlock = sched_torture_read_lock, .readlock = sched_torture_read_lock,
.read_delay = rcu_read_delay, /* just reuse rcu's version. */ .read_delay = rcu_read_delay, /* just reuse rcu's version. */
.readunlock = sched_torture_read_unlock, .readunlock = sched_torture_read_unlock,
.completed = sched_torture_completed, .completed = rcu_no_completed,
.deferred_free = rcu_sync_torture_deferred_free, .deferred_free = rcu_sync_torture_deferred_free,
.sync = synchronize_sched_expedited, .sync = synchronize_sched_expedited,
.cb_barrier = NULL, .cb_barrier = NULL,
...@@ -1116,7 +1131,8 @@ rcu_torture_init(void) ...@@ -1116,7 +1131,8 @@ rcu_torture_init(void)
int cpu; int cpu;
int firsterr = 0; int firsterr = 0;
static struct rcu_torture_ops *torture_ops[] = static struct rcu_torture_ops *torture_ops[] =
{ &rcu_ops, &rcu_sync_ops, &rcu_bh_ops, &rcu_bh_sync_ops, { &rcu_ops, &rcu_sync_ops, &rcu_expedited_ops,
&rcu_bh_ops, &rcu_bh_sync_ops,
&srcu_ops, &srcu_expedited_ops, &srcu_ops, &srcu_expedited_ops,
&sched_ops, &sched_sync_ops, &sched_expedited_ops, }; &sched_ops, &sched_sync_ops, &sched_expedited_ops, };
......
...@@ -948,7 +948,7 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp) ...@@ -948,7 +948,7 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
{ {
unsigned long flags; unsigned long flags;
unsigned long mask; unsigned long mask;
int need_quiet = 0; int need_report = 0;
struct rcu_data *rdp = rsp->rda[cpu]; struct rcu_data *rdp = rsp->rda[cpu];
struct rcu_node *rnp; struct rcu_node *rnp;
...@@ -967,7 +967,7 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp) ...@@ -967,7 +967,7 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
break; break;
} }
if (rnp == rdp->mynode) if (rnp == rdp->mynode)
need_quiet = rcu_preempt_offline_tasks(rsp, rnp, rdp); need_report = rcu_preempt_offline_tasks(rsp, rnp, rdp);
else else
spin_unlock(&rnp->lock); /* irqs remain disabled. */ spin_unlock(&rnp->lock); /* irqs remain disabled. */
mask = rnp->grpmask; mask = rnp->grpmask;
...@@ -982,10 +982,12 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp) ...@@ -982,10 +982,12 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
*/ */
spin_unlock(&rsp->onofflock); /* irqs remain disabled. */ spin_unlock(&rsp->onofflock); /* irqs remain disabled. */
rnp = rdp->mynode; rnp = rdp->mynode;
if (need_quiet) if (need_report & RCU_OFL_TASKS_NORM_GP)
rcu_report_unblock_qs_rnp(rnp, flags); rcu_report_unblock_qs_rnp(rnp, flags);
else else
spin_unlock_irqrestore(&rnp->lock, flags); spin_unlock_irqrestore(&rnp->lock, flags);
if (need_report & RCU_OFL_TASKS_EXP_GP)
rcu_report_exp_rnp(rsp, rnp);
rcu_adopt_orphan_cbs(rsp); rcu_adopt_orphan_cbs(rsp);
} }
...@@ -1843,6 +1845,8 @@ static void __init rcu_init_one(struct rcu_state *rsp) ...@@ -1843,6 +1845,8 @@ static void __init rcu_init_one(struct rcu_state *rsp)
rnp->level = i; rnp->level = i;
INIT_LIST_HEAD(&rnp->blocked_tasks[0]); INIT_LIST_HEAD(&rnp->blocked_tasks[0]);
INIT_LIST_HEAD(&rnp->blocked_tasks[1]); INIT_LIST_HEAD(&rnp->blocked_tasks[1]);
INIT_LIST_HEAD(&rnp->blocked_tasks[2]);
INIT_LIST_HEAD(&rnp->blocked_tasks[3]);
} }
} }
} }
......
...@@ -104,8 +104,12 @@ struct rcu_node { ...@@ -104,8 +104,12 @@ struct rcu_node {
/* an rcu_data structure, otherwise, each */ /* an rcu_data structure, otherwise, each */
/* bit corresponds to a child rcu_node */ /* bit corresponds to a child rcu_node */
/* structure. */ /* structure. */
unsigned long expmask; /* Groups that have ->blocked_tasks[] */
/* elements that need to drain to allow the */
/* current expedited grace period to */
/* complete (only for TREE_PREEMPT_RCU). */
unsigned long qsmaskinit; unsigned long qsmaskinit;
/* Per-GP initialization for qsmask. */ /* Per-GP initial value for qsmask & expmask. */
unsigned long grpmask; /* Mask to apply to parent qsmask. */ unsigned long grpmask; /* Mask to apply to parent qsmask. */
/* Only one bit will be set in this mask. */ /* Only one bit will be set in this mask. */
int grplo; /* lowest-numbered CPU or group here. */ int grplo; /* lowest-numbered CPU or group here. */
...@@ -113,7 +117,7 @@ struct rcu_node { ...@@ -113,7 +117,7 @@ struct rcu_node {
u8 grpnum; /* CPU/group number for next level up. */ u8 grpnum; /* CPU/group number for next level up. */
u8 level; /* root is at level 0. */ u8 level; /* root is at level 0. */
struct rcu_node *parent; struct rcu_node *parent;
struct list_head blocked_tasks[2]; struct list_head blocked_tasks[4];
/* Tasks blocked in RCU read-side critsect. */ /* Tasks blocked in RCU read-side critsect. */
/* Grace period number (->gpnum) x blocked */ /* Grace period number (->gpnum) x blocked */
/* by tasks on the (x & 0x1) element of the */ /* by tasks on the (x & 0x1) element of the */
...@@ -128,6 +132,21 @@ struct rcu_node { ...@@ -128,6 +132,21 @@ struct rcu_node {
for ((rnp) = &(rsp)->node[0]; \ for ((rnp) = &(rsp)->node[0]; \
(rnp) < &(rsp)->node[NUM_RCU_NODES]; (rnp)++) (rnp) < &(rsp)->node[NUM_RCU_NODES]; (rnp)++)
/*
* Do a breadth-first scan of the non-leaf rcu_node structures for the
* specified rcu_state structure. Note that if there is a singleton
* rcu_node tree with but one rcu_node structure, this loop is a no-op.
*/
#define rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) \
for ((rnp) = &(rsp)->node[0]; \
(rnp) < (rsp)->level[NUM_RCU_LVLS - 1]; (rnp)++)
/*
* Scan the leaves of the rcu_node hierarchy for the specified rcu_state
* structure. Note that if there is a singleton rcu_node tree with but
* one rcu_node structure, this loop -will- visit the rcu_node structure.
* It is still a leaf node, even if it is also the root node.
*/
#define rcu_for_each_leaf_node(rsp, rnp) \ #define rcu_for_each_leaf_node(rsp, rnp) \
for ((rnp) = (rsp)->level[NUM_RCU_LVLS - 1]; \ for ((rnp) = (rsp)->level[NUM_RCU_LVLS - 1]; \
(rnp) < &(rsp)->node[NUM_RCU_NODES]; (rnp)++) (rnp) < &(rsp)->node[NUM_RCU_NODES]; (rnp)++)
...@@ -261,7 +280,7 @@ struct rcu_state { ...@@ -261,7 +280,7 @@ struct rcu_state {
long gpnum; /* Current gp number. */ long gpnum; /* Current gp number. */
long completed; /* # of last completed gp. */ long completed; /* # of last completed gp. */
/* End of fields guarded by root rcu_node's lock. */ /* End of fields guarded by root rcu_node's lock. */
spinlock_t onofflock; /* exclude on/offline and */ spinlock_t onofflock; /* exclude on/offline and */
/* starting new GP. Also */ /* starting new GP. Also */
...@@ -293,6 +312,13 @@ struct rcu_state { ...@@ -293,6 +312,13 @@ struct rcu_state {
#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
}; };
/* Return values for rcu_preempt_offline_tasks(). */
#define RCU_OFL_TASKS_NORM_GP 0x1 /* Tasks blocking normal */
/* GP were moved to root. */
#define RCU_OFL_TASKS_EXP_GP 0x2 /* Tasks blocking expedited */
/* GP were moved to root. */
#ifdef RCU_TREE_NONCORE #ifdef RCU_TREE_NONCORE
/* /*
...@@ -333,6 +359,9 @@ static void rcu_preempt_offline_cpu(int cpu); ...@@ -333,6 +359,9 @@ static void rcu_preempt_offline_cpu(int cpu);
static void rcu_preempt_check_callbacks(int cpu); static void rcu_preempt_check_callbacks(int cpu);
static void rcu_preempt_process_callbacks(void); static void rcu_preempt_process_callbacks(void);
void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)); void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu));
#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_TREE_PREEMPT_RCU)
static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp);
#endif /* #if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_TREE_PREEMPT_RCU) */
static int rcu_preempt_pending(int cpu); static int rcu_preempt_pending(int cpu);
static int rcu_preempt_needs_cpu(int cpu); static int rcu_preempt_needs_cpu(int cpu);
static void __cpuinit rcu_preempt_init_percpu_data(int cpu); static void __cpuinit rcu_preempt_init_percpu_data(int cpu);
......
...@@ -24,12 +24,15 @@ ...@@ -24,12 +24,15 @@
* Paul E. McKenney <paulmck@linux.vnet.ibm.com> * Paul E. McKenney <paulmck@linux.vnet.ibm.com>
*/ */
#include <linux/delay.h>
#ifdef CONFIG_TREE_PREEMPT_RCU #ifdef CONFIG_TREE_PREEMPT_RCU
struct rcu_state rcu_preempt_state = RCU_STATE_INITIALIZER(rcu_preempt_state); struct rcu_state rcu_preempt_state = RCU_STATE_INITIALIZER(rcu_preempt_state);
DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data); DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data);
static int rcu_preempted_readers_exp(struct rcu_node *rnp);
/* /*
* Tell them what RCU they are running. * Tell them what RCU they are running.
*/ */
...@@ -157,7 +160,10 @@ EXPORT_SYMBOL_GPL(__rcu_read_lock); ...@@ -157,7 +160,10 @@ EXPORT_SYMBOL_GPL(__rcu_read_lock);
*/ */
static int rcu_preempted_readers(struct rcu_node *rnp) static int rcu_preempted_readers(struct rcu_node *rnp)
{ {
return !list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1]); int phase = rnp->gpnum & 0x1;
return !list_empty(&rnp->blocked_tasks[phase]) ||
!list_empty(&rnp->blocked_tasks[phase + 2]);
} }
/* /*
...@@ -204,6 +210,7 @@ static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags) ...@@ -204,6 +210,7 @@ static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
static void rcu_read_unlock_special(struct task_struct *t) static void rcu_read_unlock_special(struct task_struct *t)
{ {
int empty; int empty;
int empty_exp;
unsigned long flags; unsigned long flags;
struct rcu_node *rnp; struct rcu_node *rnp;
int special; int special;
...@@ -247,6 +254,8 @@ static void rcu_read_unlock_special(struct task_struct *t) ...@@ -247,6 +254,8 @@ static void rcu_read_unlock_special(struct task_struct *t)
spin_unlock(&rnp->lock); /* irqs remain disabled. */ spin_unlock(&rnp->lock); /* irqs remain disabled. */
} }
empty = !rcu_preempted_readers(rnp); empty = !rcu_preempted_readers(rnp);
empty_exp = !rcu_preempted_readers_exp(rnp);
smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
list_del_init(&t->rcu_node_entry); list_del_init(&t->rcu_node_entry);
t->rcu_blocked_node = NULL; t->rcu_blocked_node = NULL;
...@@ -259,6 +268,13 @@ static void rcu_read_unlock_special(struct task_struct *t) ...@@ -259,6 +268,13 @@ static void rcu_read_unlock_special(struct task_struct *t)
spin_unlock_irqrestore(&rnp->lock, flags); spin_unlock_irqrestore(&rnp->lock, flags);
else else
rcu_report_unblock_qs_rnp(rnp, flags); rcu_report_unblock_qs_rnp(rnp, flags);
/*
* If this was the last task on the expedited lists,
* then we need to report up the rcu_node hierarchy.
*/
if (!empty_exp && !rcu_preempted_readers_exp(rnp))
rcu_report_exp_rnp(&rcu_preempt_state, rnp);
} else { } else {
local_irq_restore(flags); local_irq_restore(flags);
} }
...@@ -343,7 +359,7 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp, ...@@ -343,7 +359,7 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
int i; int i;
struct list_head *lp; struct list_head *lp;
struct list_head *lp_root; struct list_head *lp_root;
int retval; int retval = 0;
struct rcu_node *rnp_root = rcu_get_root(rsp); struct rcu_node *rnp_root = rcu_get_root(rsp);
struct task_struct *tp; struct task_struct *tp;
...@@ -353,7 +369,9 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp, ...@@ -353,7 +369,9 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
} }
WARN_ON_ONCE(rnp != rdp->mynode && WARN_ON_ONCE(rnp != rdp->mynode &&
(!list_empty(&rnp->blocked_tasks[0]) || (!list_empty(&rnp->blocked_tasks[0]) ||
!list_empty(&rnp->blocked_tasks[1]))); !list_empty(&rnp->blocked_tasks[1]) ||
!list_empty(&rnp->blocked_tasks[2]) ||
!list_empty(&rnp->blocked_tasks[3])));
/* /*
* Move tasks up to root rcu_node. Rely on the fact that the * Move tasks up to root rcu_node. Rely on the fact that the
...@@ -361,8 +379,11 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp, ...@@ -361,8 +379,11 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
* rcu_nodes in terms of gp_num value. This fact allows us to * rcu_nodes in terms of gp_num value. This fact allows us to
* move the blocked_tasks[] array directly, element by element. * move the blocked_tasks[] array directly, element by element.
*/ */
retval = rcu_preempted_readers(rnp); if (rcu_preempted_readers(rnp))
for (i = 0; i < 2; i++) { retval |= RCU_OFL_TASKS_NORM_GP;
if (rcu_preempted_readers_exp(rnp))
retval |= RCU_OFL_TASKS_EXP_GP;
for (i = 0; i < 4; i++) {
lp = &rnp->blocked_tasks[i]; lp = &rnp->blocked_tasks[i];
lp_root = &rnp_root->blocked_tasks[i]; lp_root = &rnp_root->blocked_tasks[i];
while (!list_empty(lp)) { while (!list_empty(lp)) {
...@@ -449,14 +470,159 @@ void synchronize_rcu(void) ...@@ -449,14 +470,159 @@ void synchronize_rcu(void)
} }
EXPORT_SYMBOL_GPL(synchronize_rcu); EXPORT_SYMBOL_GPL(synchronize_rcu);
static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
static long sync_rcu_preempt_exp_count;
static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
/*
* Return non-zero if there are any tasks in RCU read-side critical
* sections blocking the current preemptible-RCU expedited grace period.
* If there is no preemptible-RCU expedited grace period currently in
* progress, returns zero unconditionally.
*/
static int rcu_preempted_readers_exp(struct rcu_node *rnp)
{
return !list_empty(&rnp->blocked_tasks[2]) ||
!list_empty(&rnp->blocked_tasks[3]);
}
/*
* return non-zero if there is no RCU expedited grace period in progress
* for the specified rcu_node structure, in other words, if all CPUs and
* tasks covered by the specified rcu_node structure have done their bit
* for the current expedited grace period. Works only for preemptible
* RCU -- other RCU implementation use other means.
*
* Caller must hold sync_rcu_preempt_exp_mutex.
*/
static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
{
return !rcu_preempted_readers_exp(rnp) &&
ACCESS_ONCE(rnp->expmask) == 0;
}
/*
* Report the exit from RCU read-side critical section for the last task
* that queued itself during or before the current expedited preemptible-RCU
* grace period. This event is reported either to the rcu_node structure on
* which the task was queued or to one of that rcu_node structure's ancestors,
* recursively up the tree. (Calm down, calm down, we do the recursion
* iteratively!)
*
* Caller must hold sync_rcu_preempt_exp_mutex.
*/
static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp)
{
unsigned long flags;
unsigned long mask;
spin_lock_irqsave(&rnp->lock, flags);
for (;;) {
if (!sync_rcu_preempt_exp_done(rnp))
break;
if (rnp->parent == NULL) {
wake_up(&sync_rcu_preempt_exp_wq);
break;
}
mask = rnp->grpmask;
spin_unlock(&rnp->lock); /* irqs remain disabled */
rnp = rnp->parent;
spin_lock(&rnp->lock); /* irqs already disabled */
rnp->expmask &= ~mask;
}
spin_unlock_irqrestore(&rnp->lock, flags);
}
/*
* Snapshot the tasks blocking the newly started preemptible-RCU expedited
* grace period for the specified rcu_node structure. If there are no such
* tasks, report it up the rcu_node hierarchy.
*
* Caller must hold sync_rcu_preempt_exp_mutex and rsp->onofflock.
*/
static void
sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
{
int must_wait;
spin_lock(&rnp->lock); /* irqs already disabled */
list_splice_init(&rnp->blocked_tasks[0], &rnp->blocked_tasks[2]);
list_splice_init(&rnp->blocked_tasks[1], &rnp->blocked_tasks[3]);
must_wait = rcu_preempted_readers_exp(rnp);
spin_unlock(&rnp->lock); /* irqs remain disabled */
if (!must_wait)
rcu_report_exp_rnp(rsp, rnp);
}
/* /*
* Wait for an rcu-preempt grace period. We are supposed to expedite the * Wait for an rcu-preempt grace period, but expedite it. The basic idea
* grace period, but this is the crude slow compatability hack, so just * is to invoke synchronize_sched_expedited() to push all the tasks to
* invoke synchronize_rcu(). * the ->blocked_tasks[] lists, move all entries from the first set of
* ->blocked_tasks[] lists to the second set, and finally wait for this
* second set to drain.
*/ */
void synchronize_rcu_expedited(void) void synchronize_rcu_expedited(void)
{ {
synchronize_rcu(); unsigned long flags;
struct rcu_node *rnp;
struct rcu_state *rsp = &rcu_preempt_state;
long snap;
int trycount = 0;
smp_mb(); /* Caller's modifications seen first by other CPUs. */
snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1;
smp_mb(); /* Above access cannot bleed into critical section. */
/*
* Acquire lock, falling back to synchronize_rcu() if too many
* lock-acquisition failures. Of course, if someone does the
* expedited grace period for us, just leave.
*/
while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) {
if (trycount++ < 10)
udelay(trycount * num_online_cpus());
else {
synchronize_rcu();
return;
}
if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0)
goto mb_ret; /* Others did our work for us. */
}
if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0)
goto unlock_mb_ret; /* Others did our work for us. */
/* force all RCU readers onto blocked_tasks[]. */
synchronize_sched_expedited();
spin_lock_irqsave(&rsp->onofflock, flags);
/* Initialize ->expmask for all non-leaf rcu_node structures. */
rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) {
spin_lock(&rnp->lock); /* irqs already disabled. */
rnp->expmask = rnp->qsmaskinit;
spin_unlock(&rnp->lock); /* irqs remain disabled. */
}
/* Snapshot current state of ->blocked_tasks[] lists. */
rcu_for_each_leaf_node(rsp, rnp)
sync_rcu_preempt_exp_init(rsp, rnp);
if (NUM_RCU_NODES > 1)
sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp));
spin_unlock_irqrestore(&rsp->onofflock, flags);
/* Wait for snapshotted ->blocked_tasks[] lists to drain. */
rnp = rcu_get_root(rsp);
wait_event(sync_rcu_preempt_exp_wq,
sync_rcu_preempt_exp_done(rnp));
/* Clean up and exit. */
smp_mb(); /* ensure expedited GP seen before counter increment. */
ACCESS_ONCE(sync_rcu_preempt_exp_count)++;
unlock_mb_ret:
mutex_unlock(&sync_rcu_preempt_exp_mutex);
mb_ret:
smp_mb(); /* ensure subsequent action seen after grace period. */
} }
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
...@@ -655,6 +821,20 @@ void synchronize_rcu_expedited(void) ...@@ -655,6 +821,20 @@ void synchronize_rcu_expedited(void)
} }
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
#ifdef CONFIG_HOTPLUG_CPU
/*
* Because preemptable RCU does not exist, there is never any need to
* report on tasks preempted in RCU read-side critical sections during
* expedited RCU grace periods.
*/
static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp)
{
return;
}
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
/* /*
* Because preemptable RCU does not exist, it never has any work to do. * Because preemptable RCU does not exist, it never has any work to do.
*/ */
......
...@@ -157,6 +157,7 @@ static void print_one_rcu_state(struct seq_file *m, struct rcu_state *rsp) ...@@ -157,6 +157,7 @@ static void print_one_rcu_state(struct seq_file *m, struct rcu_state *rsp)
{ {
long gpnum; long gpnum;
int level = 0; int level = 0;
int phase;
struct rcu_node *rnp; struct rcu_node *rnp;
gpnum = rsp->gpnum; gpnum = rsp->gpnum;
...@@ -173,10 +174,13 @@ static void print_one_rcu_state(struct seq_file *m, struct rcu_state *rsp) ...@@ -173,10 +174,13 @@ static void print_one_rcu_state(struct seq_file *m, struct rcu_state *rsp)
seq_puts(m, "\n"); seq_puts(m, "\n");
level = rnp->level; level = rnp->level;
} }
seq_printf(m, "%lx/%lx %c>%c %d:%d ^%d ", phase = gpnum & 0x1;
seq_printf(m, "%lx/%lx %c%c>%c%c %d:%d ^%d ",
rnp->qsmask, rnp->qsmaskinit, rnp->qsmask, rnp->qsmaskinit,
"T."[list_empty(&rnp->blocked_tasks[gpnum & 1])], "T."[list_empty(&rnp->blocked_tasks[phase])],
"T."[list_empty(&rnp->blocked_tasks[!(gpnum & 1)])], "E."[list_empty(&rnp->blocked_tasks[phase + 2])],
"T."[list_empty(&rnp->blocked_tasks[!phase])],
"E."[list_empty(&rnp->blocked_tasks[!phase + 2])],
rnp->grplo, rnp->grphi, rnp->grpnum); rnp->grplo, rnp->grphi, rnp->grpnum);
} }
seq_puts(m, "\n"); seq_puts(m, "\n");
......
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