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authorIngo Molnar <mingo@elte.hu>2006-01-08 12:01:37 +0300
committerLinus Torvalds <torvalds@g5.osdl.org>2006-01-09 07:13:40 +0300
commite56d090310d7625ecb43a1eeebd479f04affb48b (patch)
tree2f479215dff4a2d8f3a9ed85200a5bc4f51534be /kernel/signal.c
parent4369ef3c3e9d3bd9b879580678778f558d481e90 (diff)
downloadlinux-e56d090310d7625ecb43a1eeebd479f04affb48b.tar.xz
[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: Paul E. McKenney <paulmck@us.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu> Acked-by: William Irwin <wli@holomorphy.com> Cc: Roland McGrath <roland@redhat.com> Cc: Oleg Nesterov <oleg@tv-sign.ru> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'kernel/signal.c')
-rw-r--r--kernel/signal.c97
1 files changed, 83 insertions, 14 deletions
diff --git a/kernel/signal.c b/kernel/signal.c
index d7611f189ef7..64737c72dadd 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -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;
}
/*