linux/kernel/pid.c
Serge E. Hallyn 0f2452855d [PATCH] namespaces: fix task exit disaster
This is based on a patch by Eric W.  Biederman, who pointed out that pid
namespaces are still fake, and we only have one ever active.

So for the time being, we can modify any code which could access
tsk->nsproxy->pid_ns during task exit to just use &init_pid_ns instead,
and move the exit_task_namespaces call in do_exit() back above
exit_notify(), so that an exiting nfs server has a valid tsk->sighand to
work with.

Long term, pulling pid_ns out of nsproxy might be the cleanest solution.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

[ Eric's patch fixed to take care of free_pid() too ]

Signed-off-by: Serge E. Hallyn <serue@us.ibm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-01-30 13:40:36 -08:00

418 lines
10 KiB
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).
*/
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/bootmem.h>
#include <linux/hash.h>
#include <linux/pid_namespace.h>
#define pid_hashfn(nr) hash_long((unsigned long)nr, pidhash_shift)
static struct hlist_head *pid_hash;
static int pidhash_shift;
static struct kmem_cache *pid_cachep;
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,
.child_reaper = &init_task
};
/*
* 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 fastcall void free_pidmap(struct pid_namespace *pid_ns, int pid)
{
struct pidmap *map = pid_ns->pidmap + pid / BITS_PER_PAGE;
int offset = pid & 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;
}
static 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;
}
fastcall void put_pid(struct pid *pid)
{
if (!pid)
return;
if ((atomic_read(&pid->count) == 1) ||
atomic_dec_and_test(&pid->count))
kmem_cache_free(pid_cachep, pid);
}
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);
}
fastcall void free_pid(struct pid *pid)
{
/* We can be called with write_lock_irq(&tasklist_lock) held */
unsigned long flags;
spin_lock_irqsave(&pidmap_lock, flags);
hlist_del_rcu(&pid->pid_chain);
spin_unlock_irqrestore(&pidmap_lock, flags);
free_pidmap(&init_pid_ns, pid->nr);
call_rcu(&pid->rcu, delayed_put_pid);
}
struct pid *alloc_pid(void)
{
struct pid *pid;
enum pid_type type;
int nr = -1;
pid = kmem_cache_alloc(pid_cachep, GFP_KERNEL);
if (!pid)
goto out;
nr = alloc_pidmap(current->nsproxy->pid_ns);
if (nr < 0)
goto out_free;
atomic_set(&pid->count, 1);
pid->nr = nr;
for (type = 0; type < PIDTYPE_MAX; ++type)
INIT_HLIST_HEAD(&pid->tasks[type]);
spin_lock_irq(&pidmap_lock);
hlist_add_head_rcu(&pid->pid_chain, &pid_hash[pid_hashfn(pid->nr)]);
spin_unlock_irq(&pidmap_lock);
out:
return pid;
out_free:
kmem_cache_free(pid_cachep, pid);
pid = NULL;
goto out;
}
struct pid * fastcall find_pid(int nr)
{
struct hlist_node *elem;
struct pid *pid;
hlist_for_each_entry_rcu(pid, elem,
&pid_hash[pid_hashfn(nr)], pid_chain) {
if (pid->nr == nr)
return pid;
}
return NULL;
}
EXPORT_SYMBOL_GPL(find_pid);
int fastcall attach_pid(struct task_struct *task, enum pid_type type, int nr)
{
struct pid_link *link;
struct pid *pid;
link = &task->pids[type];
link->pid = pid = find_pid(nr);
hlist_add_head_rcu(&link->node, &pid->tasks[type]);
return 0;
}
void fastcall detach_pid(struct task_struct *task, enum pid_type type)
{
struct pid_link *link;
struct pid *pid;
int tmp;
link = &task->pids[type];
pid = link->pid;
hlist_del_rcu(&link->node);
link->pid = NULL;
for (tmp = PIDTYPE_MAX; --tmp >= 0; )
if (!hlist_empty(&pid->tasks[tmp]))
return;
free_pid(pid);
}
/* transfer_pid is an optimization of attach_pid(new), detach_pid(old) */
void fastcall 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);
old->pids[type].pid = NULL;
}
struct task_struct * fastcall 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;
}
/*
* Must be called under rcu_read_lock() or with tasklist_lock read-held.
*/
struct task_struct *find_task_by_pid_type(int type, int nr)
{
return pid_task(find_pid(nr), type);
}
EXPORT_SYMBOL(find_task_by_pid_type);
struct pid *get_task_pid(struct task_struct *task, enum pid_type type)
{
struct pid *pid;
rcu_read_lock();
pid = get_pid(task->pids[type].pid);
rcu_read_unlock();
return pid;
}
struct task_struct *fastcall 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_pid(nr));
rcu_read_unlock();
return pid;
}
/*
* Used by proc to find the first pid that is greater then or equal to nr.
*
* If there is a pid at nr this function is exactly the same as find_pid.
*/
struct pid *find_ge_pid(int nr)
{
struct pid *pid;
do {
pid = find_pid(nr);
if (pid)
break;
nr = next_pidmap(current->nsproxy->pid_ns, nr);
} while (nr > 0);
return pid;
}
EXPORT_SYMBOL_GPL(find_get_pid);
int copy_pid_ns(int flags, struct task_struct *tsk)
{
struct pid_namespace *old_ns = tsk->nsproxy->pid_ns;
int err = 0;
if (!old_ns)
return 0;
get_pid_ns(old_ns);
return err;
}
void free_pid_ns(struct kref *kref)
{
struct pid_namespace *ns;
ns = container_of(kref, struct pid_namespace, kref);
kfree(ns);
}
/*
* 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;
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,
pidhash_size * sizeof(struct hlist_head));
pid_hash = alloc_bootmem(pidhash_size * sizeof(*(pid_hash)));
if (!pid_hash)
panic("Could not alloc pidhash!\n");
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);
pid_cachep = kmem_cache_create("pid", sizeof(struct pid),
__alignof__(struct pid),
SLAB_PANIC, NULL, NULL);
}