(2006-08-06) rescue-bootcd

extra/linux-2.6.10/kernel/pid.c

@@ -0,0 +1,292 @@
+/*
+ * Generic pidhash and scalable, time-bounded PID allocator
+ *
+ * (C) 2002-2003 William Irwin, IBM
+ * (C) 2004 William Irwin, Oracle
+ * (C) 2002-2004 Ingo Molnar, Red Hat
+ *
+ * pid-structures are backing objects for tasks sharing a given ID to chain
+ * against. There is very little to them aside from hashing them and
+ * parking tasks using given ID's on a list.
+ *
+ * The hash is always changed with the tasklist_lock write-acquired,
+ * and the hash is only accessed with the tasklist_lock at least
+ * read-acquired, so there's no additional SMP locking needed here.
+ *
+ * We have a list of bitmap pages, which bitmaps represent the PID space.
+ * Allocating and freeing PIDs is completely lockless. The worst-case
+ * allocation scenario when all but one out of 1 million PIDs possible are
+ * allocated already: the scanning of 32 list entries and at most PAGE_SIZE
+ * bytes. The typical fastpath is a single successful setbit. Freeing is O(1).
+ */
+
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/init.h>
+#include <linux/bootmem.h>
+#include <linux/hash.h>
+
+#define pid_hashfn(nr) hash_long((unsigned long)nr, pidhash_shift)
+static struct hlist_head *pid_hash[PIDTYPE_MAX];
+static int pidhash_shift;
+
+int pid_max = PID_MAX_DEFAULT;
+int last_pid;
+
+#define RESERVED_PIDS		300
+
+int pid_max_min = RESERVED_PIDS + 1;
+int pid_max_max = PID_MAX_LIMIT;
+
+#define PIDMAP_ENTRIES		((PID_MAX_LIMIT + 8*PAGE_SIZE - 1)/PAGE_SIZE/8)
+#define BITS_PER_PAGE		(PAGE_SIZE*8)
+#define BITS_PER_PAGE_MASK	(BITS_PER_PAGE-1)
+#define mk_pid(map, off)	(((map) - pidmap_array)*BITS_PER_PAGE + (off))
+#define find_next_offset(map, off)					\
+		find_next_zero_bit((map)->page, BITS_PER_PAGE, off)
+
+/*
+ * PID-map pages start out as NULL, they get allocated upon
+ * first use and are never deallocated. This way a low pid_max
+ * value does not cause lots of bitmaps to be allocated, but
+ * the scheme scales to up to 4 million PIDs, runtime.
+ */
+typedef struct pidmap {
+	atomic_t nr_free;
+	void *page;
+} pidmap_t;
+
+static pidmap_t pidmap_array[PIDMAP_ENTRIES] =
+	 { [ 0 ... PIDMAP_ENTRIES-1 ] = { ATOMIC_INIT(BITS_PER_PAGE), NULL } };
+
+static spinlock_t pidmap_lock __cacheline_aligned_in_smp = SPIN_LOCK_UNLOCKED;
+
+fastcall void free_pidmap(int pid)
+{
+	pidmap_t *map = pidmap_array + pid / BITS_PER_PAGE;
+	int offset = pid & BITS_PER_PAGE_MASK;
+
+	clear_bit(offset, map->page);
+	atomic_inc(&map->nr_free);
+}
+
+int alloc_pidmap(void)
+{
+	int i, offset, max_scan, pid, last = last_pid;
+	pidmap_t *map;
+
+	pid = last + 1;
+	if (pid >= pid_max)
+		pid = RESERVED_PIDS;
+	offset = pid & BITS_PER_PAGE_MASK;
+	map = &pidmap_array[pid/BITS_PER_PAGE];
+	max_scan = (pid_max + BITS_PER_PAGE - 1)/BITS_PER_PAGE - !offset;
+	for (i = 0; i <= max_scan; ++i) {
+		if (unlikely(!map->page)) {
+			unsigned long page = get_zeroed_page(GFP_KERNEL);
+			/*
+			 * Free the page if someone raced with us
+			 * installing it:
+			 */
+			spin_lock(&pidmap_lock);
+			if (map->page)
+				free_page(page);
+			else
+				map->page = (void *)page;
+			spin_unlock(&pidmap_lock);
+			if (unlikely(!map->page))
+				break;
+		}
+		if (likely(atomic_read(&map->nr_free))) {
+			do {
+				if (!test_and_set_bit(offset, map->page)) {
+					atomic_dec(&map->nr_free);
+					last_pid = pid;
+					return pid;
+				}
+				offset = find_next_offset(map, offset);
+				pid = mk_pid(map, offset);
+			/*
+			 * find_next_offset() found a bit, the pid from it
+			 * is in-bounds, and if we fell back to the last
+			 * bitmap block and the final block was the same
+			 * as the starting point, pid is before last_pid.
+			 */
+			} while (offset < BITS_PER_PAGE && pid < pid_max &&
+					(i != max_scan || pid < last ||
+					    !((last+1) & BITS_PER_PAGE_MASK)));
+		}
+		if (map < &pidmap_array[(pid_max-1)/BITS_PER_PAGE]) {
+			++map;
+			offset = 0;
+		} else {
+			map = &pidmap_array[0];
+			offset = RESERVED_PIDS;
+			if (unlikely(last == offset))
+				break;
+		}
+		pid = mk_pid(map, offset);
+	}
+	return -1;
+}
+
+struct pid * fastcall find_pid(enum pid_type type, int nr)
+{
+	struct hlist_node *elem;
+	struct pid *pid;
+
+	hlist_for_each_entry(pid, elem,
+			&pid_hash[type][pid_hashfn(nr)], pid_chain) {
+		if (pid->nr == nr)
+			return pid;
+	}
+	return NULL;
+}
+
+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);
+	if (pid == NULL) {
+		hlist_add_head(&task_pid->pid_chain,
+				&pid_hash[type][pid_hashfn(nr)]);
+		INIT_LIST_HEAD(&task_pid->pid_list);
+	} else {
+		INIT_HLIST_NODE(&task_pid->pid_chain);
+		list_add_tail(&task_pid->pid_list, &pid->pid_list);
+	}
+	task_pid->nr = nr;
+
+	return 0;
+}
+
+static fastcall int __detach_pid(task_t *task, enum pid_type type)
+{
+	struct pid *pid, *pid_next;
+	int nr = 0;
+
+	pid = &task->pids[type];
+	if (!hlist_unhashed(&pid->pid_chain)) {
+		hlist_del(&pid->pid_chain);
+
+		if (list_empty(&pid->pid_list))
+			nr = pid->nr;
+		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)]);
+		}
+	}
+
+	list_del(&pid->pid_list);
+	pid->nr = 0;
+
+	return nr;
+}
+
+void fastcall detach_pid(task_t *task, enum pid_type type)
+{
+	int tmp, nr;
+
+	nr = __detach_pid(task, type);
+	if (!nr)
+		return;
+
+	for (tmp = PIDTYPE_MAX; --tmp >= 0; )
+		if (tmp != type && find_pid(tmp, nr))
+			return;
+
+	free_pidmap(nr);
+}
+
+task_t *find_task_by_pid_type(int type, int nr)
+{
+	struct pid *pid;
+
+	pid = find_pid(type, nr);
+	if (!pid)
+		return NULL;
+
+	return pid_task(&pid->pid_list, type);
+}
+
+EXPORT_SYMBOL(find_task_by_pid_type);
+
+/*
+ * This function switches the PIDs if a non-leader thread calls
+ * sys_execve() - this must be done without releasing the PID.
+ * (which a detach_pid() would eventually do.)
+ */
+void switch_exec_pids(task_t *leader, task_t *thread)
+{
+	__detach_pid(leader, PIDTYPE_PID);
+	__detach_pid(leader, PIDTYPE_TGID);
+	__detach_pid(leader, PIDTYPE_PGID);
+	__detach_pid(leader, PIDTYPE_SID);
+
+	__detach_pid(thread, PIDTYPE_PID);
+	__detach_pid(thread, PIDTYPE_TGID);
+
+	leader->pid = leader->tgid = thread->pid;
+	thread->pid = thread->tgid;
+
+	attach_pid(thread, PIDTYPE_PID, thread->pid);
+	attach_pid(thread, PIDTYPE_TGID, thread->tgid);
+	attach_pid(thread, PIDTYPE_PGID, thread->signal->pgrp);
+	attach_pid(thread, PIDTYPE_SID, thread->signal->session);
+	list_add_tail(&thread->tasks, &init_task.tasks);
+
+	attach_pid(leader, PIDTYPE_PID, leader->pid);
+	attach_pid(leader, PIDTYPE_TGID, leader->tgid);
+	attach_pid(leader, PIDTYPE_PGID, leader->signal->pgrp);
+	attach_pid(leader, PIDTYPE_SID, leader->signal->session);
+}
+
+/*
+ * 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
+ * more.
+ */
+void __init pidhash_init(void)
+{
+	int i, j, pidhash_size;
+	unsigned long megabytes = nr_kernel_pages >> (20 - PAGE_SHIFT);
+
+	pidhash_shift = max(4, fls(megabytes * 4));
+	pidhash_shift = min(12, pidhash_shift);
+	pidhash_size = 1 << pidhash_shift;
+
+	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]);
+	}
+}
+
+void __init pidmap_init(void)
+{
+	int i;
+
+	pidmap_array->page = (void *)get_zeroed_page(GFP_KERNEL);
+	set_bit(0, pidmap_array->page);
+	atomic_dec(&pidmap_array->nr_free);
+
+	/*
+	 * Allocate PID 0, and hash it via all PID types:
+	 */
+
+	for (i = 0; i < PIDTYPE_MAX; i++)
+		attach_pid(current, i, 0);
+}