[PATCH] RCU signal handling

[linux-2.6-omap-h63xx.git] / kernel / signal.c

diff --git a/kernel/signal.c b/kernel/signal.c
index d7611f189ef7ac33ef7610e7a92a3584f5c7028b..64737c72daddc3f7d79d800aaaa598a6a9b45be7 100644 (file)
--- 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;
 }
 
 /*