Revision 4b3be6afa4ab8b3fdce39df68bad71f8b85164de authored by Julia Lawall on 17 October 2009, 06:33:22 UTC, committed by Takashi Iwai on 30 October 2009, 11:01:27 UTC
In pcm.c, if the NULL test on pcm is needed, then the dereference should be
after the NULL test.

In dummy.c and ali5451.c, the context of the calls to
snd_card_dummy_new_mixer and snd_ali_free_voice show that dummy and pvoice,
respectively cannot be NULL.

A simplified version of the semantic match that detects this problem is as
follows (http://coccinelle.lip6.fr/):

// <smpl>
@match exists@
expression x, E;
identifier fld;
@@

* x->fld
  ... when != \(x = E\|&x\)
* x == NULL
// </smpl>

Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
1 parent b71207e
Raw File
pid.c
/*
 * 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).
 *
 * 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/module.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>

#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;

#define BITS_PER_PAGE		(PAGE_SIZE*8)
#define BITS_PER_PAGE_MASK	(BITS_PER_PAGE-1)

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,
	.level = 0,
	.child_reaper = &init_task,
};
EXPORT_SYMBOL_GPL(init_pid_ns);

int is_container_init(struct task_struct *tsk)
{
	int ret = 0;
	struct pid *pid;

	rcu_read_lock();
	pid = task_pid(tsk);
	if (pid != NULL && pid->numbers[pid->level].nr == 1)
		ret = 1;
	rcu_read_unlock();

	return ret;
}
EXPORT_SYMBOL(is_container_init);

/*
 * 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);
}

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];
	max_scan = (pid_max + BITS_PER_PAGE - 1)/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)
				kfree(page);
			else
				map->page = page;
			spin_unlock_irq(&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);
					pid_ns->last_pid = pid;
					return pid;
				}
				offset = find_next_offset(map, offset);
				pid = mk_pid(pid_ns, 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 < &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 -1;
}

int next_pidmap(struct pid_namespace *pid_ns, int last)
{
	int offset;
	struct pidmap *map, *end;

	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++)
		hlist_del_rcu(&pid->numbers[i].pid_chain);
	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;

	pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL);
	if (!pid)
		goto out;

	tmp = ns;
	for (i = ns->level; i >= 0; i--) {
		nr = alloc_pidmap(tmp);
		if (nr < 0)
			goto out_free;

		pid->numbers[i].nr = nr;
		pid->numbers[i].ns = tmp;
		tmp = tmp->parent;
	}

	get_pid_ns(ns);
	pid->level = ns->level;
	atomic_set(&pid->count, 1);
	for (type = 0; type < PIDTYPE_MAX; ++type)
		INIT_HLIST_HEAD(&pid->tasks[type]);

	spin_lock_irq(&pidmap_lock);
	for (i = ns->level; i >= 0; i--) {
		upid = &pid->numbers[i];
		hlist_add_head_rcu(&upid->pid_chain,
				&pid_hash[pid_hashfn(upid->nr, upid->ns)]);
	}
	spin_unlock_irq(&pidmap_lock);

out:
	return pid;

out_free:
	while (++i <= ns->level)
		free_pidmap(pid->numbers + i);

	kmem_cache_free(ns->pid_cachep, pid);
	pid = NULL;
	goto out;
}

struct pid *find_pid_ns(int nr, struct pid_namespace *ns)
{
	struct hlist_node *elem;
	struct upid *pnr;

	hlist_for_each_entry_rcu(pnr, elem,
			&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, current->nsproxy->pid_ns);
}
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 *pid)
{
	struct pid_link *link;

	link = &task->pids[type];
	link->pid = pid;
	hlist_add_head_rcu(&link->node, &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, pid);
}

/* 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(pid->tasks[type].first);
		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() or with tasklist_lock read-held.
 */
struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns)
{
	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, current->nsproxy->pid_ns);
}

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;
}

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;
}

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;
}

pid_t pid_vnr(struct pid *pid)
{
	return pid_nr_ns(pid, current->nsproxy->pid_ns);
}
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 = current->nsproxy->pid_ns;
	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)
{
	int i, pidhash_size;

	pid_hash = alloc_large_system_hash("PID", sizeof(*pid_hash), 0, 18,
					   HASH_EARLY | HASH_SMALL,
					   &pidhash_shift, NULL, 4096);
	pidhash_size = 1 << pidhash_shift;

	for (i = 0; i < pidhash_size; i++)
		INIT_HLIST_HEAD(&pid_hash[i]);
}

void __init pidmap_init(void)
{
	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);
}
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