/*
* 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
+ * (C) 2002 William Irwin, IBM
+ * (C) 2002 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
#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 PIDMAP_ENTRIES (PID_MAX_LIMIT/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
static pidmap_t pidmap_array[PIDMAP_ENTRIES] =
{ [ 0 ... PIDMAP_ENTRIES-1 ] = { ATOMIC_INIT(BITS_PER_PAGE), NULL } };
+static pidmap_t *map_limit = pidmap_array + PIDMAP_ENTRIES;
+
static spinlock_t pidmap_lock __cacheline_aligned_in_smp = SPIN_LOCK_UNLOCKED;
fastcall void free_pidmap(int pid)
atomic_inc(&map->nr_free);
}
-int alloc_pidmap(void)
+/*
+ * Here we search for the next map that has free bits left.
+ * Normally the next map has free PIDs.
+ */
+static inline pidmap_t *next_free_map(pidmap_t *map, int *max_steps)
{
- 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) {
+ while (--*max_steps) {
+ if (++map == map_limit)
+ map = pidmap_array;
if (unlikely(!map->page)) {
unsigned long page = get_zeroed_page(GFP_KERNEL);
/*
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))
+
+ if (!map->page)
break;
}
- pid = mk_pid(map, offset);
+ if (atomic_read(&map->nr_free))
+ return map;
}
+ return NULL;
+}
+
+int alloc_pidmap(void)
+{
+ int pid, offset, max_steps = PIDMAP_ENTRIES + 1;
+ pidmap_t *map;
+
+ pid = last_pid + 1;
+ if (pid >= pid_max)
+ pid = RESERVED_PIDS;
+
+ offset = pid & BITS_PER_PAGE_MASK;
+ map = pidmap_array + pid / BITS_PER_PAGE;
+
+ if (likely(map->page && !test_and_set_bit(offset, map->page))) {
+ /*
+ * There is a small window for last_pid updates to race,
+ * but in that case the next allocation will go into the
+ * slowpath and that fixes things up.
+ */
+return_pid:
+ atomic_dec(&map->nr_free);
+ last_pid = pid;
+ return pid;
+ }
+
+ if (!offset || !atomic_read(&map->nr_free)) {
+next_map:
+ map = next_free_map(map, &max_steps);
+ if (!map)
+ goto failure;
+ offset = 0;
+ }
+ /*
+ * Find the next zero bit:
+ */
+scan_more:
+ offset = find_next_zero_bit(map->page, BITS_PER_PAGE, offset);
+ if (offset >= BITS_PER_PAGE)
+ goto next_map;
+ if (test_and_set_bit(offset, map->page))
+ goto scan_more;
+
+ /* we got the PID: */
+ pid = (map - pidmap_array) * BITS_PER_PAGE + offset;
+ goto return_pid;
+
+failure:
return -1;
}
return 0;
}
-static fastcall int __detach_pid(task_t *task, enum pid_type type)
+static inline int __detach_pid(task_t *task, enum pid_type type)
{
struct pid *pid, *pid_next;
- int nr = 0;
+ int nr;
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 {
+ if (!list_empty(&pid->pid_list)) {
pid_next = list_entry(pid->pid_list.next,
struct pid, pid_list);
/* insert next pid from pid_list to hash */
&pid_hash[type][pid_hashfn(pid_next->nr)]);
}
}
-
list_del(&pid->pid_list);
+ nr = pid->nr;
pid->nr = 0;
return nr;
void fastcall detach_pid(task_t *task, enum pid_type type)
{
- int tmp, nr;
+ int nr;
nr = __detach_pid(task, type);
if (!nr)
return;
- for (tmp = PIDTYPE_MAX; --tmp >= 0; )
- if (tmp != type && find_pid(tmp, nr))
+ for (type = 0; type < PIDTYPE_MAX; ++type)
+ if (find_pid(type, nr))
return;
-
free_pidmap(nr);
}
attach_pid(leader, PIDTYPE_SID, leader->signal->session);
}
+/**
+ * pid_alive - check that a task structure is not stale
+ * @p: Task structure to be checked.
+ *
+ * Test if a process is not yet dead (at most zombie state)
+ * If pid_alive fails, then pointers within the task structure
+ * can be stale and must not be dereferenced.
+ */
+int pid_alive(struct task_struct *p)
+{
+ return p->pids[PIDTYPE_PID].nr != 0;
+}
+
/*
* 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
git://git.onelab.eu / linux-2.6.git / blobdiff