1 files changed, 146 insertions, 66 deletions

diff --git a/kernel/pid.c b/kernel/pid.c
index a9f2dfd..eeb836b 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -28,8 +28,9 @@
 #include <linux/hash.h>
 
 #define pid_hashfn(nr) hash_long((unsigned long)nr, pidhash_shift)
-static struct hlist_head *pid_hash[PIDTYPE_MAX];
+static struct hlist_head *pid_hash;
 static int pidhash_shift;
+static kmem_cache_t *pid_cachep;
 
 int pid_max = PID_MAX_DEFAULT;
 int last_pid;
@@ -60,9 +61,22 @@ typedef struct pidmap {
 static pidmap_t pidmap_array[PIDMAP_ENTRIES] =
 	 { [ 0 ... PIDMAP_ENTRIES-1 ] = { ATOMIC_INIT(BITS_PER_PAGE), NULL } };
 
+/*
+ * Note: disable interrupts while the pidmap_lock is held as an
+ * interrupt might come in and do read_lock(&tasklist_lock).
+ *
+ * If we don't disable interrupts there is a nasty deadlock between
+ * detach_pid()->free_pid() and another cpu that does
+ * spin_lock(&pidmap_lock) followed by an interrupt routine that does
+ * read_lock(&tasklist_lock);
+ *
+ * After we clean up the tasklist_lock and know there are no
+ * irq handlers that take it we can leave the interrupts enabled.
+ * For now it is easier to be safe than to prove it can't happen.
+ */
 static  __cacheline_aligned_in_smp DEFINE_SPINLOCK(pidmap_lock);
 
-fastcall void free_pidmap(int pid)
+static fastcall void free_pidmap(int pid)
 {
 	pidmap_t *map = pidmap_array + pid / BITS_PER_PAGE;
 	int offset = pid & BITS_PER_PAGE_MASK;
@@ -71,7 +85,7 @@ fastcall void free_pidmap(int pid)
 	atomic_inc(&map->nr_free);
 }
 
-int alloc_pidmap(void)
+static int alloc_pidmap(void)
 {
 	int i, offset, max_scan, pid, last = last_pid;
 	pidmap_t *map;
@@ -89,12 +103,12 @@ int alloc_pidmap(void)
 			 * Free the page if someone raced with us
 			 * installing it:
 			 */
-			spin_lock(&pidmap_lock);
+			spin_lock_irq(&pidmap_lock);
 			if (map->page)
 				free_page(page);
 			else
 				map->page = (void *)page;
-			spin_unlock(&pidmap_lock);
+			spin_unlock_irq(&pidmap_lock);
 			if (unlikely(!map->page))
 				break;
 		}
@@ -131,13 +145,73 @@ int alloc_pidmap(void)
 	return -1;
 }
 
-struct pid * fastcall find_pid(enum pid_type type, int nr)
+fastcall void put_pid(struct pid *pid)
+{
+	if (!pid)
+		return;
+	if ((atomic_read(&pid->count) == 1) ||
+	     atomic_dec_and_test(&pid->count))
+		kmem_cache_free(pid_cachep, pid);
+}
+
+static void delayed_put_pid(struct rcu_head *rhp)
+{
+	struct pid *pid = container_of(rhp, struct pid, rcu);
+	put_pid(pid);
+}
+
+fastcall void free_pid(struct pid *pid)
+{
+	/* We can be called with write_lock_irq(&tasklist_lock) held */
+	unsigned long flags;
+
+	spin_lock_irqsave(&pidmap_lock, flags);
+	hlist_del_rcu(&pid->pid_chain);
+	spin_unlock_irqrestore(&pidmap_lock, flags);
+
+	free_pidmap(pid->nr);
+	call_rcu(&pid->rcu, delayed_put_pid);
+}
+
+struct pid *alloc_pid(void)
+{
+	struct pid *pid;
+	enum pid_type type;
+	int nr = -1;
+
+	pid = kmem_cache_alloc(pid_cachep, GFP_KERNEL);
+	if (!pid)
+		goto out;
+
+	nr = alloc_pidmap();
+	if (nr < 0)
+		goto out_free;
+
+	atomic_set(&pid->count, 1);
+	pid->nr = nr;
+	for (type = 0; type < PIDTYPE_MAX; ++type)
+		INIT_HLIST_HEAD(&pid->tasks[type]);
+
+	spin_lock_irq(&pidmap_lock);
+	hlist_add_head_rcu(&pid->pid_chain, &pid_hash[pid_hashfn(pid->nr)]);
+	spin_unlock_irq(&pidmap_lock);
+
+out:
+	return pid;
+
+out_free:
+	kmem_cache_free(pid_cachep, pid);
+	pid = NULL;
+	goto out;
+}
+
+struct pid * fastcall find_pid(int nr)
 {
 	struct hlist_node *elem;
 	struct pid *pid;
 
 	hlist_for_each_entry_rcu(pid, elem,
-			&pid_hash[type][pid_hashfn(nr)], pid_chain) {
+			&pid_hash[pid_hashfn(nr)], pid_chain) {
 		if (pid->nr == nr)
 			return pid;
 	}
@@ -146,77 +220,82 @@ struct pid * fastcall find_pid(enum pid_type type, int nr)
 
 int fastcall attach_pid(task_t *task, enum pid_type type, int nr)
 {
-	struct pid *pid, *task_pid;
-
-	task_pid = &task->pids[type];
-	pid = find_pid(type, nr);
-	task_pid->nr = nr;
-	if (pid == NULL) {
-		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_rcu(&task_pid->pid_list, &pid->pid_list);
-	}
+	struct pid_link *link;
+	struct pid *pid;
+
+	WARN_ON(!task->pid); /* to be removed soon */
+	WARN_ON(!nr); /* to be removed soon */
+
+	link = &task->pids[type];
+	link->pid = pid = find_pid(nr);
+	hlist_add_head_rcu(&link->node, &pid->tasks[type]);
 
 	return 0;
 }
 
-static fastcall int __detach_pid(task_t *task, enum pid_type type)
+void fastcall detach_pid(task_t *task, enum pid_type type)
 {
-	struct pid *pid, *pid_next;
-	int nr = 0;
+	struct pid_link *link;
+	struct pid *pid;
+	int tmp;
 
-	pid = &task->pids[type];
-	if (!hlist_unhashed(&pid->pid_chain)) {
+	link = &task->pids[type];
+	pid = link->pid;
 
-		if (list_empty(&pid->pid_list)) {
-			nr = pid->nr;
-			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_replace_rcu(&pid->pid_chain,
-					  &pid_next->pid_chain);
-		}
-	}
+	hlist_del_rcu(&link->node);
+	link->pid = NULL;
 
-	list_del_rcu(&pid->pid_list);
-	pid->nr = 0;
+	for (tmp = PIDTYPE_MAX; --tmp >= 0; )
+		if (!hlist_empty(&pid->tasks[tmp]))
+			return;
 
-	return nr;
+	free_pid(pid);
 }
 
-void fastcall detach_pid(task_t *task, enum pid_type type)
+struct task_struct * fastcall pid_task(struct pid *pid, enum pid_type type)
 {
-	int tmp, nr;
+	struct task_struct *result = NULL;
+	if (pid) {
+		struct hlist_node *first;
+		first = rcu_dereference(pid->tasks[type].first);
+		if (first)
+			result = hlist_entry(first, struct task_struct, pids[(type)].node);
+	}
+	return result;
+}
 
-	nr = __detach_pid(task, type);
-	if (!nr)
-		return;
+/*
+ * Must be called under rcu_read_lock() or with tasklist_lock read-held.
+ */
+task_t *find_task_by_pid_type(int type, int nr)
+{
+	return pid_task(find_pid(nr), type);
+}
 
-	for (tmp = PIDTYPE_MAX; --tmp >= 0; )
-		if (tmp != type && find_pid(tmp, nr))
-			return;
+EXPORT_SYMBOL(find_task_by_pid_type);
 
-	free_pidmap(nr);
+struct task_struct *fastcall get_pid_task(struct pid *pid, enum pid_type type)
+{
+	struct task_struct *result;
+	rcu_read_lock();
+	result = pid_task(pid, type);
+	if (result)
+		get_task_struct(result);
+	rcu_read_unlock();
+	return result;
 }
 
-task_t *find_task_by_pid_type(int type, int nr)
+struct pid *find_get_pid(pid_t nr)
 {
 	struct pid *pid;
 
-	pid = find_pid(type, nr);
-	if (!pid)
-		return NULL;
+	rcu_read_lock();
+	pid = get_pid(find_pid(nr));
+	rcu_read_unlock();
 
-	return pid_task(&pid->pid_list, type);
+	return pid;
 }
 
-EXPORT_SYMBOL(find_task_by_pid_type);
-
 /*
  * The pid hash table is scaled according to the amount of memory in the
  * machine.  From a minimum of 16 slots up to 4096 slots at one gigabyte or
@@ -224,7 +303,7 @@ EXPORT_SYMBOL(find_task_by_pid_type);
  */
 void __init pidhash_init(void)
 {
-	int i, j, pidhash_size;
+	int i, pidhash_size;
 	unsigned long megabytes = nr_kernel_pages >> (20 - PAGE_SHIFT);
 
 	pidhash_shift = max(4, fls(megabytes * 4));
@@ -233,16 +312,13 @@ void __init pidhash_init(void)
 
 	printk("PID hash table entries: %d (order: %d, %Zd bytes)\n",
 		pidhash_size, pidhash_shift,
-		PIDTYPE_MAX * pidhash_size * sizeof(struct hlist_head));
-
-	for (i = 0; i < PIDTYPE_MAX; i++) {
-		pid_hash[i] = alloc_bootmem(pidhash_size *
-					sizeof(*(pid_hash[i])));
-		if (!pid_hash[i])
-			panic("Could not alloc pidhash!\n");
-		for (j = 0; j < pidhash_size; j++)
-			INIT_HLIST_HEAD(&pid_hash[i][j]);
-	}
+		pidhash_size * sizeof(struct hlist_head));
+
+	pid_hash = alloc_bootmem(pidhash_size *	sizeof(*(pid_hash)));
+	if (!pid_hash)
+		panic("Could not alloc pidhash!\n");
+	for (i = 0; i < pidhash_size; i++)
+		INIT_HLIST_HEAD(&pid_hash[i]);
 }
 
 void __init pidmap_init(void)
@@ -251,4 +327,8 @@ void __init pidmap_init(void)
 	/* Reserve PID 0. We never call free_pidmap(0) */
 	set_bit(0, pidmap_array->page);
 	atomic_dec(&pidmap_array->nr_free);
+
+	pid_cachep = kmem_cache_create("pid", sizeof(struct pid),
+					__alignof__(struct pid),
+					SLAB_PANIC, NULL, NULL);
 }