Linux-2.6.12-rc2
Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.
Let it rip!
diff --git a/kernel/pid.c b/kernel/pid.c
new file mode 100644
index 0000000..edba31c
--- /dev/null
+++ b/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 __cacheline_aligned_in_smp DEFINE_SPINLOCK(pidmap_lock);
+
+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);
+}