--- /dev/null
+/*
+ * Generic pidhash and scalable, time-bounded PID allocator
+ *
+ * (C) 2002-2003 Nadia Yvette Chambers, IBM
+ * (C) 2004 Nadia Yvette Chambers, 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).
+ *
+ * Pid namespaces:
+ * (C) 2007 Pavel Emelyanov <xemul@openvz.org>, OpenVZ, SWsoft Inc.
+ * (C) 2007 Sukadev Bhattiprolu <sukadev@us.ibm.com>, IBM
+ * Many thanks to Oleg Nesterov for comments and help
+ *
+ */
+
+#include <linux/mm.h>
+#include <linux/export.h>
+#include <linux/slab.h>
+#include <linux/init.h>
+#include <linux/rculist.h>
+#include <linux/bootmem.h>
+#include <linux/hash.h>
+#include <linux/pid_namespace.h>
+#include <linux/init_task.h>
+#include <linux/syscalls.h>
+#include <linux/proc_ns.h>
+#include <linux/proc_fs.h>
+
+#define pid_hashfn(nr, ns) \
+ hash_long((unsigned long)nr + (unsigned long)ns, pidhash_shift)
+static struct hlist_head *pid_hash;
+static unsigned int pidhash_shift = 4;
+struct pid init_struct_pid = INIT_STRUCT_PID;
+
+int pid_max = PID_MAX_DEFAULT;
+
+#define RESERVED_PIDS 300
+
+int pid_max_min = RESERVED_PIDS + 1;
+int pid_max_max = PID_MAX_LIMIT;
+
+static inline int mk_pid(struct pid_namespace *pid_ns,
+ struct pidmap *map, int off)
+{
+ return (map - pid_ns->pidmap)*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.
+ */
+struct pid_namespace init_pid_ns = {
+ .kref = {
+ .refcount = ATOMIC_INIT(2),
+ },
+ .pidmap = {
+ [ 0 ... PIDMAP_ENTRIES-1] = { ATOMIC_INIT(BITS_PER_PAGE), NULL }
+ },
+ .last_pid = 0,
+ .nr_hashed = PIDNS_HASH_ADDING,
+ .level = 0,
+ .child_reaper = &init_task,
+ .user_ns = &init_user_ns,
+ .ns.inum = PROC_PID_INIT_INO,
+#ifdef CONFIG_PID_NS
+ .ns.ops = &pidns_operations,
+#endif
+};
+EXPORT_SYMBOL_GPL(init_pid_ns);
+
+/*
+ * 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);
+
+static void free_pidmap(struct upid *upid)
+{
+ int nr = upid->nr;
+ struct pidmap *map = upid->ns->pidmap + nr / BITS_PER_PAGE;
+ int offset = nr & BITS_PER_PAGE_MASK;
+
+ clear_bit(offset, map->page);
+ atomic_inc(&map->nr_free);
+}
+
+/*
+ * If we started walking pids at 'base', is 'a' seen before 'b'?
+ */
+static int pid_before(int base, int a, int b)
+{
+ /*
+ * This is the same as saying
+ *
+ * (a - base + MAXUINT) % MAXUINT < (b - base + MAXUINT) % MAXUINT
+ * and that mapping orders 'a' and 'b' with respect to 'base'.
+ */
+ return (unsigned)(a - base) < (unsigned)(b - base);
+}
+
+/*
+ * We might be racing with someone else trying to set pid_ns->last_pid
+ * at the pid allocation time (there's also a sysctl for this, but racing
+ * with this one is OK, see comment in kernel/pid_namespace.c about it).
+ * We want the winner to have the "later" value, because if the
+ * "earlier" value prevails, then a pid may get reused immediately.
+ *
+ * Since pids rollover, it is not sufficient to just pick the bigger
+ * value. We have to consider where we started counting from.
+ *
+ * 'base' is the value of pid_ns->last_pid that we observed when
+ * we started looking for a pid.
+ *
+ * 'pid' is the pid that we eventually found.
+ */
+static void set_last_pid(struct pid_namespace *pid_ns, int base, int pid)
+{
+ int prev;
+ int last_write = base;
+ do {
+ prev = last_write;
+ last_write = cmpxchg(&pid_ns->last_pid, prev, pid);
+ } while ((prev != last_write) && (pid_before(base, last_write, pid)));
+}
+
+static int alloc_pidmap(struct pid_namespace *pid_ns)
+{
+ int i, offset, max_scan, pid, last = pid_ns->last_pid;
+ struct pidmap *map;
+
+ pid = last + 1;
+ if (pid >= pid_max)
+ pid = RESERVED_PIDS;
+ offset = pid & BITS_PER_PAGE_MASK;
+ map = &pid_ns->pidmap[pid/BITS_PER_PAGE];
+ /*
+ * If last_pid points into the middle of the map->page we
+ * want to scan this bitmap block twice, the second time
+ * we start with offset == 0 (or RESERVED_PIDS).
+ */
+ max_scan = DIV_ROUND_UP(pid_max, BITS_PER_PAGE) - !offset;
+ for (i = 0; i <= max_scan; ++i) {
+ if (unlikely(!map->page)) {
+ void *page = kzalloc(PAGE_SIZE, GFP_KERNEL);
+ /*
+ * Free the page if someone raced with us
+ * installing it:
+ */
+ spin_lock_irq(&pidmap_lock);
+ if (!map->page) {
+ map->page = page;
+ page = NULL;
+ }
+ spin_unlock_irq(&pidmap_lock);
+ kfree(page);
+ if (unlikely(!map->page))
+ return -ENOMEM;
+ }
+ if (likely(atomic_read(&map->nr_free))) {
+ for ( ; ; ) {
+ if (!test_and_set_bit(offset, map->page)) {
+ atomic_dec(&map->nr_free);
+ set_last_pid(pid_ns, last, pid);
+ return pid;
+ }
+ offset = find_next_offset(map, offset);
+ if (offset >= BITS_PER_PAGE)
+ break;
+ pid = mk_pid(pid_ns, map, offset);
+ if (pid >= pid_max)
+ break;
+ }
+ }
+ if (map < &pid_ns->pidmap[(pid_max-1)/BITS_PER_PAGE]) {
+ ++map;
+ offset = 0;
+ } else {
+ map = &pid_ns->pidmap[0];
+ offset = RESERVED_PIDS;
+ if (unlikely(last == offset))
+ break;
+ }
+ pid = mk_pid(pid_ns, map, offset);
+ }
+ return -EAGAIN;
+}
+
+int next_pidmap(struct pid_namespace *pid_ns, unsigned int last)
+{
+ int offset;
+ struct pidmap *map, *end;
+
+ if (last >= PID_MAX_LIMIT)
+ return -1;
+
+ offset = (last + 1) & BITS_PER_PAGE_MASK;
+ map = &pid_ns->pidmap[(last + 1)/BITS_PER_PAGE];
+ end = &pid_ns->pidmap[PIDMAP_ENTRIES];
+ for (; map < end; map++, offset = 0) {
+ if (unlikely(!map->page))
+ continue;
+ offset = find_next_bit((map)->page, BITS_PER_PAGE, offset);
+ if (offset < BITS_PER_PAGE)
+ return mk_pid(pid_ns, map, offset);
+ }
+ return -1;
+}
+
+void put_pid(struct pid *pid)
+{
+ struct pid_namespace *ns;
+
+ if (!pid)
+ return;
+
+ ns = pid->numbers[pid->level].ns;
+ if ((atomic_read(&pid->count) == 1) ||
+ atomic_dec_and_test(&pid->count)) {
+ kmem_cache_free(ns->pid_cachep, pid);
+ put_pid_ns(ns);
+ }
+}
+EXPORT_SYMBOL_GPL(put_pid);
+
+static void delayed_put_pid(struct rcu_head *rhp)
+{
+ struct pid *pid = container_of(rhp, struct pid, rcu);
+ put_pid(pid);
+}
+
+void free_pid(struct pid *pid)
+{
+ /* We can be called with write_lock_irq(&tasklist_lock) held */
+ int i;
+ unsigned long flags;
+
+ spin_lock_irqsave(&pidmap_lock, flags);
+ for (i = 0; i <= pid->level; i++) {
+ struct upid *upid = pid->numbers + i;
+ struct pid_namespace *ns = upid->ns;
+ hlist_del_rcu(&upid->pid_chain);
+ switch(--ns->nr_hashed) {
+ case 2:
+ case 1:
+ /* When all that is left in the pid namespace
+ * is the reaper wake up the reaper. The reaper
+ * may be sleeping in zap_pid_ns_processes().
+ */
+ wake_up_process(ns->child_reaper);
+ break;
+ case PIDNS_HASH_ADDING:
+ /* Handle a fork failure of the first process */
+ WARN_ON(ns->child_reaper);
+ ns->nr_hashed = 0;
+ /* fall through */
+ case 0:
+ schedule_work(&ns->proc_work);
+ break;
+ }
+ }
+ spin_unlock_irqrestore(&pidmap_lock, flags);
+
+ for (i = 0; i <= pid->level; i++)
+ free_pidmap(pid->numbers + i);
+
+ call_rcu(&pid->rcu, delayed_put_pid);
+}
+
+struct pid *alloc_pid(struct pid_namespace *ns)
+{
+ struct pid *pid;
+ enum pid_type type;
+ int i, nr;
+ struct pid_namespace *tmp;
+ struct upid *upid;
+ int retval = -ENOMEM;
+
+ pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL);
+ if (!pid)
+ return ERR_PTR(retval);
+
+ tmp = ns;
+ pid->level = ns->level;
+ for (i = ns->level; i >= 0; i--) {
+ nr = alloc_pidmap(tmp);
+ if (IS_ERR_VALUE(nr)) {
+ retval = nr;
+ goto out_free;
+ }
+
+ pid->numbers[i].nr = nr;
+ pid->numbers[i].ns = tmp;
+ tmp = tmp->parent;
+ }
+
+ if (unlikely(is_child_reaper(pid))) {
+ if (pid_ns_prepare_proc(ns))
+ goto out_free;
+ }
+
+ get_pid_ns(ns);
+ atomic_set(&pid->count, 1);
+ for (type = 0; type < PIDTYPE_MAX; ++type)
+ INIT_HLIST_HEAD(&pid->tasks[type]);
+
+ upid = pid->numbers + ns->level;
+ spin_lock_irq(&pidmap_lock);
+ if (!(ns->nr_hashed & PIDNS_HASH_ADDING))
+ goto out_unlock;
+ for ( ; upid >= pid->numbers; --upid) {
+ hlist_add_head_rcu(&upid->pid_chain,
+ &pid_hash[pid_hashfn(upid->nr, upid->ns)]);
+ upid->ns->nr_hashed++;
+ }
+ spin_unlock_irq(&pidmap_lock);
+
+ return pid;
+
+out_unlock:
+ spin_unlock_irq(&pidmap_lock);
+ put_pid_ns(ns);
+
+out_free:
+ while (++i <= ns->level)
+ free_pidmap(pid->numbers + i);
+
+ kmem_cache_free(ns->pid_cachep, pid);
+ return ERR_PTR(retval);
+}
+
+void disable_pid_allocation(struct pid_namespace *ns)
+{
+ spin_lock_irq(&pidmap_lock);
+ ns->nr_hashed &= ~PIDNS_HASH_ADDING;
+ spin_unlock_irq(&pidmap_lock);
+}
+
+struct pid *find_pid_ns(int nr, struct pid_namespace *ns)
+{
+ struct upid *pnr;
+
+ hlist_for_each_entry_rcu(pnr,
+ &pid_hash[pid_hashfn(nr, ns)], pid_chain)
+ if (pnr->nr == nr && pnr->ns == ns)
+ return container_of(pnr, struct pid,
+ numbers[ns->level]);
+
+ return NULL;
+}
+EXPORT_SYMBOL_GPL(find_pid_ns);
+
+struct pid *find_vpid(int nr)
+{
+ return find_pid_ns(nr, task_active_pid_ns(current));
+}
+EXPORT_SYMBOL_GPL(find_vpid);
+
+/*
+ * attach_pid() must be called with the tasklist_lock write-held.
+ */
+void attach_pid(struct task_struct *task, enum pid_type type)
+{
+ struct pid_link *link = &task->pids[type];
+ hlist_add_head_rcu(&link->node, &link->pid->tasks[type]);
+}
+
+static void __change_pid(struct task_struct *task, enum pid_type type,
+ struct pid *new)
+{
+ struct pid_link *link;
+ struct pid *pid;
+ int tmp;
+
+ link = &task->pids[type];
+ pid = link->pid;
+
+ hlist_del_rcu(&link->node);
+ link->pid = new;
+
+ for (tmp = PIDTYPE_MAX; --tmp >= 0; )
+ if (!hlist_empty(&pid->tasks[tmp]))
+ return;
+
+ free_pid(pid);
+}
+
+void detach_pid(struct task_struct *task, enum pid_type type)
+{
+ __change_pid(task, type, NULL);
+}
+
+void change_pid(struct task_struct *task, enum pid_type type,
+ struct pid *pid)
+{
+ __change_pid(task, type, pid);
+ attach_pid(task, type);
+}
+
+/* transfer_pid is an optimization of attach_pid(new), detach_pid(old) */
+void transfer_pid(struct task_struct *old, struct task_struct *new,
+ enum pid_type type)
+{
+ new->pids[type].pid = old->pids[type].pid;
+ hlist_replace_rcu(&old->pids[type].node, &new->pids[type].node);
+}
+
+struct task_struct *pid_task(struct pid *pid, enum pid_type type)
+{
+ struct task_struct *result = NULL;
+ if (pid) {
+ struct hlist_node *first;
+ first = rcu_dereference_check(hlist_first_rcu(&pid->tasks[type]),
+ lockdep_tasklist_lock_is_held());
+ if (first)
+ result = hlist_entry(first, struct task_struct, pids[(type)].node);
+ }
+ return result;
+}
+EXPORT_SYMBOL(pid_task);
+
+/*
+ * Must be called under rcu_read_lock().
+ */
+struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns)
+{
+ rcu_lockdep_assert(rcu_read_lock_held(),
+ "find_task_by_pid_ns() needs rcu_read_lock()"
+ " protection");
+ return pid_task(find_pid_ns(nr, ns), PIDTYPE_PID);
+}
+
+struct task_struct *find_task_by_vpid(pid_t vnr)
+{
+ return find_task_by_pid_ns(vnr, task_active_pid_ns(current));
+}
+
+struct pid *get_task_pid(struct task_struct *task, enum pid_type type)
+{
+ struct pid *pid;
+ rcu_read_lock();
+ if (type != PIDTYPE_PID)
+ task = task->group_leader;
+ pid = get_pid(task->pids[type].pid);
+ rcu_read_unlock();
+ return pid;
+}
+EXPORT_SYMBOL_GPL(get_task_pid);
+
+struct task_struct *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;
+}
+EXPORT_SYMBOL_GPL(get_pid_task);
+
+struct pid *find_get_pid(pid_t nr)
+{
+ struct pid *pid;
+
+ rcu_read_lock();
+ pid = get_pid(find_vpid(nr));
+ rcu_read_unlock();
+
+ return pid;
+}
+EXPORT_SYMBOL_GPL(find_get_pid);
+
+pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns)
+{
+ struct upid *upid;
+ pid_t nr = 0;
+
+ if (pid && ns->level <= pid->level) {
+ upid = &pid->numbers[ns->level];
+ if (upid->ns == ns)
+ nr = upid->nr;
+ }
+ return nr;
+}
+EXPORT_SYMBOL_GPL(pid_nr_ns);
+
+pid_t pid_vnr(struct pid *pid)
+{
+ return pid_nr_ns(pid, task_active_pid_ns(current));
+}
+EXPORT_SYMBOL_GPL(pid_vnr);
+
+pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type,
+ struct pid_namespace *ns)
+{
+ pid_t nr = 0;
+
+ rcu_read_lock();
+ if (!ns)
+ ns = task_active_pid_ns(current);
+ if (likely(pid_alive(task))) {
+ if (type != PIDTYPE_PID)
+ task = task->group_leader;
+ nr = pid_nr_ns(task->pids[type].pid, ns);
+ }
+ rcu_read_unlock();
+
+ return nr;
+}
+EXPORT_SYMBOL(__task_pid_nr_ns);
+
+pid_t task_tgid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
+{
+ return pid_nr_ns(task_tgid(tsk), ns);
+}
+EXPORT_SYMBOL(task_tgid_nr_ns);
+
+struct pid_namespace *task_active_pid_ns(struct task_struct *tsk)
+{
+ return ns_of_pid(task_pid(tsk));
+}
+EXPORT_SYMBOL_GPL(task_active_pid_ns);
+
+/*
+ * Used by proc to find the first pid that is greater than or equal to nr.
+ *
+ * If there is a pid at nr this function is exactly the same as find_pid_ns.
+ */
+struct pid *find_ge_pid(int nr, struct pid_namespace *ns)
+{
+ struct pid *pid;
+
+ do {
+ pid = find_pid_ns(nr, ns);
+ if (pid)
+ break;
+ nr = next_pidmap(ns, nr);
+ } while (nr > 0);
+
+ return pid;
+}
+
+/*
+ * 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)
+{
+ unsigned int i, pidhash_size;
+
+ pid_hash = alloc_large_system_hash("PID", sizeof(*pid_hash), 0, 18,
+ HASH_EARLY | HASH_SMALL,
+ &pidhash_shift, NULL,
+ 0, 4096);
+ pidhash_size = 1U << pidhash_shift;
+
+ for (i = 0; i < pidhash_size; i++)
+ INIT_HLIST_HEAD(&pid_hash[i]);
+}
+
+void __init pidmap_init(void)
+{
+ /* Veryify no one has done anything silly */
+ BUILD_BUG_ON(PID_MAX_LIMIT >= PIDNS_HASH_ADDING);
+
+ /* bump default and minimum pid_max based on number of cpus */
+ pid_max = min(pid_max_max, max_t(int, pid_max,
+ PIDS_PER_CPU_DEFAULT * num_possible_cpus()));
+ pid_max_min = max_t(int, pid_max_min,
+ PIDS_PER_CPU_MIN * num_possible_cpus());
+ pr_info("pid_max: default: %u minimum: %u\n", pid_max, pid_max_min);
+
+ init_pid_ns.pidmap[0].page = kzalloc(PAGE_SIZE, GFP_KERNEL);
+ /* Reserve PID 0. We never call free_pidmap(0) */
+ set_bit(0, init_pid_ns.pidmap[0].page);
+ atomic_dec(&init_pid_ns.pidmap[0].nr_free);
+
+ init_pid_ns.pid_cachep = KMEM_CACHE(pid,
+ SLAB_HWCACHE_ALIGN | SLAB_PANIC);
+}
Code Review / kvmfornfv.git / blobdiff