Commit e56d0903 authored by Ingo Molnar's avatar Ingo Molnar Committed by Linus Torvalds
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[PATCH] RCU signal handling



RCU tasklist_lock and RCU signal handling: send signals RCU-read-locked
instead of tasklist_lock read-locked.  This is a scalability improvement on
SMP and a preemption-latency improvement under PREEMPT_RCU.
Signed-off-by: default avatarPaul E. McKenney <paulmck@us.ibm.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Acked-by: default avatarWilliam Irwin <wli@holomorphy.com>
Cc: Roland McGrath <roland@redhat.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 4369ef3c
......@@ -760,7 +760,7 @@ static inline int de_thread(struct task_struct *tsk)
spin_lock(&oldsighand->siglock);
spin_lock(&newsighand->siglock);
current->sighand = newsighand;
rcu_assign_pointer(current->sighand, newsighand);
recalc_sigpending();
spin_unlock(&newsighand->siglock);
......@@ -768,7 +768,7 @@ static inline int de_thread(struct task_struct *tsk)
write_unlock_irq(&tasklist_lock);
if (atomic_dec_and_test(&oldsighand->count))
kmem_cache_free(sighand_cachep, oldsighand);
sighand_free(oldsighand);
}
BUG_ON(!thread_group_leader(current));
......
......@@ -34,6 +34,7 @@
#include <linux/percpu.h>
#include <linux/topology.h>
#include <linux/seccomp.h>
#include <linux/rcupdate.h>
#include <linux/auxvec.h> /* For AT_VECTOR_SIZE */
......@@ -350,8 +351,16 @@ struct sighand_struct {
atomic_t count;
struct k_sigaction action[_NSIG];
spinlock_t siglock;
struct rcu_head rcu;
};
extern void sighand_free_cb(struct rcu_head *rhp);
static inline void sighand_free(struct sighand_struct *sp)
{
call_rcu(&sp->rcu, sighand_free_cb);
}
/*
* NOTE! "signal_struct" does not have it's own
* locking, because a shared signal_struct always
......@@ -844,6 +853,7 @@ struct task_struct {
int cpuset_mems_generation;
#endif
atomic_t fs_excl; /* holding fs exclusive resources */
struct rcu_head rcu;
};
static inline pid_t process_group(struct task_struct *tsk)
......@@ -867,8 +877,26 @@ static inline int pid_alive(struct task_struct *p)
extern void free_task(struct task_struct *tsk);
extern void __put_task_struct(struct task_struct *tsk);
#define get_task_struct(tsk) do { atomic_inc(&(tsk)->usage); } while(0)
#define put_task_struct(tsk) \
do { if (atomic_dec_and_test(&(tsk)->usage)) __put_task_struct(tsk); } while(0)
static inline int get_task_struct_rcu(struct task_struct *t)
{
int oldusage;
do {
oldusage = atomic_read(&t->usage);
if (oldusage == 0)
return 0;
} while (cmpxchg(&t->usage.counter, oldusage, oldusage+1) != oldusage);
return 1;
}
extern void __put_task_struct_cb(struct rcu_head *rhp);
static inline void put_task_struct(struct task_struct *t)
{
if (atomic_dec_and_test(&t->usage))
call_rcu(&t->rcu, __put_task_struct_cb);
}
/*
* Per process flags
......
......@@ -72,7 +72,6 @@ void release_task(struct task_struct * p)
__ptrace_unlink(p);
BUG_ON(!list_empty(&p->ptrace_list) || !list_empty(&p->ptrace_children));
__exit_signal(p);
__exit_sighand(p);
/*
* Note that the fastpath in sys_times depends on __exit_signal having
* updated the counters before a task is removed from the tasklist of
......
......@@ -743,6 +743,14 @@ int unshare_files(void)
EXPORT_SYMBOL(unshare_files);
void sighand_free_cb(struct rcu_head *rhp)
{
struct sighand_struct *sp;
sp = container_of(rhp, struct sighand_struct, rcu);
kmem_cache_free(sighand_cachep, sp);
}
static inline int copy_sighand(unsigned long clone_flags, struct task_struct * tsk)
{
struct sighand_struct *sig;
......@@ -752,7 +760,7 @@ static inline int copy_sighand(unsigned long clone_flags, struct task_struct * t
return 0;
}
sig = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
tsk->sighand = sig;
rcu_assign_pointer(tsk->sighand, sig);
if (!sig)
return -ENOMEM;
spin_lock_init(&sig->siglock);
......
......@@ -136,7 +136,7 @@ struct pid * fastcall find_pid(enum pid_type type, int nr)
struct hlist_node *elem;
struct pid *pid;
hlist_for_each_entry(pid, elem,
hlist_for_each_entry_rcu(pid, elem,
&pid_hash[type][pid_hashfn(nr)], pid_chain) {
if (pid->nr == nr)
return pid;
......@@ -150,15 +150,15 @@ int fastcall attach_pid(task_t *task, enum pid_type type, int nr)
task_pid = &task->pids[type];
pid = find_pid(type, nr);
task_pid->nr = nr;
if (pid == NULL) {
hlist_add_head(&task_pid->pid_chain,
&pid_hash[type][pid_hashfn(nr)]);
INIT_LIST_HEAD(&task_pid->pid_list);
hlist_add_head_rcu(&task_pid->pid_chain,
&pid_hash[type][pid_hashfn(nr)]);
} else {
INIT_HLIST_NODE(&task_pid->pid_chain);
list_add_tail(&task_pid->pid_list, &pid->pid_list);
list_add_tail_rcu(&task_pid->pid_list, &pid->pid_list);
}
task_pid->nr = nr;
return 0;
}
......@@ -170,20 +170,20 @@ static fastcall int __detach_pid(task_t *task, enum pid_type type)
pid = &task->pids[type];
if (!hlist_unhashed(&pid->pid_chain)) {
hlist_del(&pid->pid_chain);
if (list_empty(&pid->pid_list))
if (list_empty(&pid->pid_list)) {
nr = pid->nr;
else {
hlist_del_rcu(&pid->pid_chain);
} else {
pid_next = list_entry(pid->pid_list.next,
struct pid, pid_list);
/* insert next pid from pid_list to hash */
hlist_add_head(&pid_next->pid_chain,
&pid_hash[type][pid_hashfn(pid_next->nr)]);
hlist_replace_rcu(&pid->pid_chain,
&pid_next->pid_chain);
}
}
list_del(&pid->pid_list);
list_del_rcu(&pid->pid_list);
pid->nr = 0;
return nr;
......
......@@ -35,6 +35,7 @@
#include <linux/init.h>
#include <linux/spinlock.h>
#include <linux/smp.h>
#include <linux/rcupdate.h>
#include <linux/interrupt.h>
#include <linux/sched.h>
#include <asm/atomic.h>
......
......@@ -176,6 +176,13 @@ static unsigned int task_timeslice(task_t *p)
#define task_hot(p, now, sd) ((long long) ((now) - (p)->last_ran) \
< (long long) (sd)->cache_hot_time)
void __put_task_struct_cb(struct rcu_head *rhp)
{
__put_task_struct(container_of(rhp, struct task_struct, rcu));
}
EXPORT_SYMBOL_GPL(__put_task_struct_cb);
/*
* These are the runqueue data structures:
*/
......
......@@ -329,13 +329,20 @@ void __exit_sighand(struct task_struct *tsk)
/* Ok, we're done with the signal handlers */
tsk->sighand = NULL;
if (atomic_dec_and_test(&sighand->count))
kmem_cache_free(sighand_cachep, sighand);
sighand_free(sighand);
}
void exit_sighand(struct task_struct *tsk)
{
write_lock_irq(&tasklist_lock);
__exit_sighand(tsk);
rcu_read_lock();
if (tsk->sighand != NULL) {
struct sighand_struct *sighand = rcu_dereference(tsk->sighand);
spin_lock(&sighand->siglock);
__exit_sighand(tsk);
spin_unlock(&sighand->siglock);
}
rcu_read_unlock();
write_unlock_irq(&tasklist_lock);
}
......@@ -345,12 +352,14 @@ void exit_sighand(struct task_struct *tsk)
void __exit_signal(struct task_struct *tsk)
{
struct signal_struct * sig = tsk->signal;
struct sighand_struct * sighand = tsk->sighand;
struct sighand_struct * sighand;
if (!sig)
BUG();
if (!atomic_read(&sig->count))
BUG();
rcu_read_lock();
sighand = rcu_dereference(tsk->sighand);
spin_lock(&sighand->siglock);
posix_cpu_timers_exit(tsk);
if (atomic_dec_and_test(&sig->count)) {
......@@ -358,6 +367,7 @@ void __exit_signal(struct task_struct *tsk)
if (tsk == sig->curr_target)
sig->curr_target = next_thread(tsk);
tsk->signal = NULL;
__exit_sighand(tsk);
spin_unlock(&sighand->siglock);
flush_sigqueue(&sig->shared_pending);
} else {
......@@ -389,9 +399,11 @@ void __exit_signal(struct task_struct *tsk)
sig->nvcsw += tsk->nvcsw;
sig->nivcsw += tsk->nivcsw;
sig->sched_time += tsk->sched_time;
__exit_sighand(tsk);
spin_unlock(&sighand->siglock);
sig = NULL; /* Marker for below. */
}
rcu_read_unlock();
clear_tsk_thread_flag(tsk,TIF_SIGPENDING);
flush_sigqueue(&tsk->pending);
if (sig) {
......@@ -1080,18 +1092,28 @@ void zap_other_threads(struct task_struct *p)
}
/*
* Must be called with the tasklist_lock held for reading!
* Must be called under rcu_read_lock() or with tasklist_lock read-held.
*/
int group_send_sig_info(int sig, struct siginfo *info, struct task_struct *p)
{
unsigned long flags;
struct sighand_struct *sp;
int ret;
retry:
ret = check_kill_permission(sig, info, p);
if (!ret && sig && p->sighand) {
spin_lock_irqsave(&p->sighand->siglock, flags);
if (!ret && sig && (sp = p->sighand)) {
if (!get_task_struct_rcu(p))
return -ESRCH;
spin_lock_irqsave(&sp->siglock, flags);
if (p->sighand != sp) {
spin_unlock_irqrestore(&sp->siglock, flags);
put_task_struct(p);
goto retry;
}
ret = __group_send_sig_info(sig, info, p);
spin_unlock_irqrestore(&p->sighand->siglock, flags);
spin_unlock_irqrestore(&sp->siglock, flags);
put_task_struct(p);
}
return ret;
......@@ -1136,14 +1158,21 @@ int
kill_proc_info(int sig, struct siginfo *info, pid_t pid)
{
int error;
int acquired_tasklist_lock = 0;
struct task_struct *p;
read_lock(&tasklist_lock);
rcu_read_lock();
if (unlikely(sig_kernel_stop(sig) || sig == SIGCONT)) {
read_lock(&tasklist_lock);
acquired_tasklist_lock = 1;
}
p = find_task_by_pid(pid);
error = -ESRCH;
if (p)
error = group_send_sig_info(sig, info, p);
read_unlock(&tasklist_lock);
if (unlikely(acquired_tasklist_lock))
read_unlock(&tasklist_lock);
rcu_read_unlock();
return error;
}
......@@ -1355,16 +1384,54 @@ send_sigqueue(int sig, struct sigqueue *q, struct task_struct *p)
{
unsigned long flags;
int ret = 0;
struct sighand_struct *sh;
BUG_ON(!(q->flags & SIGQUEUE_PREALLOC));
read_lock(&tasklist_lock);
/*
* The rcu based delayed sighand destroy makes it possible to
* run this without tasklist lock held. The task struct itself
* cannot go away as create_timer did get_task_struct().
*
* We return -1, when the task is marked exiting, so
* posix_timer_event can redirect it to the group leader
*/
rcu_read_lock();
if (unlikely(p->flags & PF_EXITING)) {
ret = -1;
goto out_err;
}
spin_lock_irqsave(&p->sighand->siglock, flags);
retry:
sh = rcu_dereference(p->sighand);
spin_lock_irqsave(&sh->siglock, flags);
if (p->sighand != sh) {
/* We raced with exec() in a multithreaded process... */
spin_unlock_irqrestore(&sh->siglock, flags);
goto retry;
}
/*
* We do the check here again to handle the following scenario:
*
* CPU 0 CPU 1
* send_sigqueue
* check PF_EXITING
* interrupt exit code running
* __exit_signal
* lock sighand->siglock
* unlock sighand->siglock
* lock sh->siglock
* add(tsk->pending) flush_sigqueue(tsk->pending)
*
*/
if (unlikely(p->flags & PF_EXITING)) {
ret = -1;
goto out;
}
if (unlikely(!list_empty(&q->list))) {
/*
......@@ -1388,9 +1455,9 @@ send_sigqueue(int sig, struct sigqueue *q, struct task_struct *p)
signal_wake_up(p, sig == SIGKILL);
out:
spin_unlock_irqrestore(&p->sighand->siglock, flags);
spin_unlock_irqrestore(&sh->siglock, flags);
out_err:
read_unlock(&tasklist_lock);
rcu_read_unlock();
return ret;
}
......@@ -1402,7 +1469,9 @@ send_group_sigqueue(int sig, struct sigqueue *q, struct task_struct *p)
int ret = 0;
BUG_ON(!(q->flags & SIGQUEUE_PREALLOC));
read_lock(&tasklist_lock);
/* Since it_lock is held, p->sighand cannot be NULL. */
spin_lock_irqsave(&p->sighand->siglock, flags);
handle_stop_signal(sig, p);
......@@ -1436,7 +1505,7 @@ send_group_sigqueue(int sig, struct sigqueue *q, struct task_struct *p)
out:
spin_unlock_irqrestore(&p->sighand->siglock, flags);
read_unlock(&tasklist_lock);
return(ret);
return ret;
}
/*
......
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