Linux-2.6.12-rc2v2.6.12-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!

1 files changed, 292 insertions, 0 deletions

diff --git a/kernel/pid.c b/kernel/pid.c
new file mode 100644
index 000000000000..edba31c681ac
--- /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);
+}