#ifndef _LINUX_PID_H
#define _LINUX_PID_H
+#include <linux/rcupdate.h>
+
enum pid_type
{
PIDTYPE_PID,
PIDTYPE_MAX
};
+/*
+ * What is struct pid?
+ *
+ * A struct pid is the kernel's internal notion of a process identifier.
+ * It refers to individual tasks, process groups, and sessions. While
+ * there are processes attached to it the struct pid lives in a hash
+ * table, so it and then the processes that it refers to can be found
+ * quickly from the numeric pid value. The attached processes may be
+ * quickly accessed by following pointers from struct pid.
+ *
+ * Storing pid_t values in the kernel and refering to them later has a
+ * problem. The process originally with that pid may have exited and the
+ * pid allocator wrapped, and another process could have come along
+ * and been assigned that pid.
+ *
+ * Referring to user space processes by holding a reference to struct
+ * task_struct has a problem. When the user space process exits
+ * the now useless task_struct is still kept. A task_struct plus a
+ * stack consumes around 10K of low kernel memory. More precisely
+ * this is THREAD_SIZE + sizeof(struct task_struct). By comparison
+ * a struct pid is about 64 bytes.
+ *
+ * Holding a reference to struct pid solves both of these problems.
+ * It is small so holding a reference does not consume a lot of
+ * resources, and since a new struct pid is allocated when the numeric
+ * pid value is reused we don't mistakenly refer to new processes.
+ */
+
struct pid
{
+ atomic_t count;
/* Try to keep pid_chain in the same cacheline as nr for find_pid */
int nr;
struct hlist_node pid_chain;
- /* list of pids with the same nr, only one of them is in the hash */
- struct list_head pid_list;
+ /* lists of tasks that use this pid */
+ struct hlist_head tasks[PIDTYPE_MAX];
+ struct rcu_head rcu;
};
-#define pid_task(elem, type) \
- list_entry(elem, struct task_struct, pids[type].pid_list)
+struct pid_link
+{
+ struct hlist_node node;
+ struct pid *pid;
+};
+
+static inline struct pid *get_pid(struct pid *pid)
+{
+ if (pid)
+ atomic_inc(&pid->count);
+ return pid;
+}
+
+extern void FASTCALL(put_pid(struct pid *pid));
+extern struct task_struct *FASTCALL(pid_task(struct pid *pid, enum pid_type));
+extern struct task_struct *FASTCALL(get_pid_task(struct pid *pid,
+ enum pid_type));
/*
* attach_pid() and detach_pid() must be called with the tasklist_lock
* write-held.
*/
-extern int FASTCALL(attach_pid(struct task_struct *task, enum pid_type type, int nr));
+extern int FASTCALL(attach_pid(struct task_struct *task,
+ enum pid_type type, int nr));
extern void FASTCALL(detach_pid(struct task_struct *task, enum pid_type));
/*
* look up a PID in the hash table. Must be called with the tasklist_lock
- * held.
+ * or rcu_read_lock() held.
+ */
+extern struct pid *FASTCALL(find_pid(int nr));
+
+/*
+ * Lookup a PID in the hash table, and return with it's count elevated.
*/
-extern struct pid *FASTCALL(find_pid(enum pid_type, int));
+extern struct pid *find_get_pid(int nr);
-extern int alloc_pidmap(void);
-extern void FASTCALL(free_pidmap(int));
+extern struct pid *alloc_pid(void);
+extern void FASTCALL(free_pid(struct pid *pid));
+#define pid_next(task, type) \
+ ((task)->pids[(type)].node.next)
+
+#define pid_next_task(task, type) \
+ hlist_entry(pid_next(task, type), struct task_struct, \
+ pids[(type)].node)
+
+
+/* We could use hlist_for_each_entry_rcu here but it takes more arguments
+ * than the do_each_task_pid/while_each_task_pid. So we roll our own
+ * to preserve the existing interface.
+ */
#define do_each_task_pid(who, type, task) \
if ((task = find_task_by_pid_type(type, who))) { \
- prefetch((task)->pids[type].pid_list.next); \
+ prefetch(pid_next(task, type)); \
do {
#define while_each_task_pid(who, type, task) \
- } while (task = pid_task((task)->pids[type].pid_list.next,\
- type), \
- prefetch((task)->pids[type].pid_list.next), \
- hlist_unhashed(&(task)->pids[type].pid_chain)); \
- } \
+ } while (pid_next(task, type) && ({ \
+ task = pid_next_task(task, type); \
+ rcu_dereference(task); \
+ prefetch(pid_next(task, type)); \
+ 1; }) ); \
+ }
#endif /* _LINUX_PID_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 struct hlist_head *pid_hash;
static int pidhash_shift;
+static kmem_cache_t *pid_cachep;
int pid_max = PID_MAX_DEFAULT;
int last_pid;
static pidmap_t pidmap_array[PIDMAP_ENTRIES] =
{ [ 0 ... PIDMAP_ENTRIES-1 ] = { ATOMIC_INIT(BITS_PER_PAGE), NULL } };
+/*
+ * 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);
-fastcall void free_pidmap(int pid)
+static fastcall void free_pidmap(int pid)
{
pidmap_t *map = pidmap_array + pid / BITS_PER_PAGE;
int offset = pid & BITS_PER_PAGE_MASK;
atomic_inc(&map->nr_free);
}
-int alloc_pidmap(void)
+static int alloc_pidmap(void)
{
int i, offset, max_scan, pid, last = last_pid;
pidmap_t *map;
* Free the page if someone raced with us
* installing it:
*/
- spin_lock(&pidmap_lock);
+ spin_lock_irq(&pidmap_lock);
if (map->page)
free_page(page);
else
map->page = (void *)page;
- spin_unlock(&pidmap_lock);
+ spin_unlock_irq(&pidmap_lock);
if (unlikely(!map->page))
break;
}
return -1;
}
-struct pid * fastcall find_pid(enum pid_type type, int nr)
+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);
+}
+
+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(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();
+ 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[type][pid_hashfn(nr)], pid_chain) {
+ &pid_hash[pid_hashfn(nr)], pid_chain) {
if (pid->nr == nr)
return pid;
}
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);
- task_pid->nr = nr;
- if (pid == NULL) {
- INIT_LIST_HEAD(&task_pid->pid_list);
- hlist_add_head_rcu(&task_pid->pid_chain,
- &pid_hash[type][pid_hashfn(nr)]);
- } else {
- INIT_HLIST_NODE(&task_pid->pid_chain);
- list_add_tail_rcu(&task_pid->pid_list, &pid->pid_list);
- }
+ struct pid_link *link;
+ struct pid *pid;
+
+ WARN_ON(!task->pid); /* to be removed soon */
+ WARN_ON(!nr); /* to be removed soon */
+
+ link = &task->pids[type];
+ link->pid = pid = find_pid(nr);
+ hlist_add_head_rcu(&link->node, &pid->tasks[type]);
return 0;
}
-static fastcall int __detach_pid(task_t *task, enum pid_type type)
+void fastcall detach_pid(task_t *task, enum pid_type type)
{
- struct pid *pid, *pid_next;
- int nr = 0;
+ struct pid_link *link;
+ struct pid *pid;
+ int tmp;
- pid = &task->pids[type];
- if (!hlist_unhashed(&pid->pid_chain)) {
+ link = &task->pids[type];
+ pid = link->pid;
- if (list_empty(&pid->pid_list)) {
- nr = pid->nr;
- hlist_del_rcu(&pid->pid_chain);
- } else {
- pid_next = list_entry(pid->pid_list.next,
- struct pid, pid_list);
- /* insert next pid from pid_list to hash */
- hlist_replace_rcu(&pid->pid_chain,
- &pid_next->pid_chain);
- }
- }
+ hlist_del_rcu(&link->node);
+ link->pid = NULL;
- list_del_rcu(&pid->pid_list);
- pid->nr = 0;
+ for (tmp = PIDTYPE_MAX; --tmp >= 0; )
+ if (!hlist_empty(&pid->tasks[tmp]))
+ return;
- return nr;
+ free_pid(pid);
}
-void fastcall detach_pid(task_t *task, enum pid_type type)
+struct task_struct * fastcall pid_task(struct pid *pid, enum pid_type type)
{
- int tmp, nr;
+ 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;
+}
- nr = __detach_pid(task, type);
- if (!nr)
- return;
+/*
+ * Must be called under rcu_read_lock() or with tasklist_lock read-held.
+ */
+task_t *find_task_by_pid_type(int type, int nr)
+{
+ return pid_task(find_pid(nr), type);
+}
- for (tmp = PIDTYPE_MAX; --tmp >= 0; )
- if (tmp != type && find_pid(tmp, nr))
- return;
+EXPORT_SYMBOL(find_task_by_pid_type);
- free_pidmap(nr);
+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;
}
-task_t *find_task_by_pid_type(int type, int nr)
+struct pid *find_get_pid(pid_t nr)
{
struct pid *pid;
- pid = find_pid(type, nr);
- if (!pid)
- return NULL;
+ rcu_read_lock();
+ pid = get_pid(find_pid(nr));
+ rcu_read_unlock();
- return pid_task(&pid->pid_list, type);
+ return pid;
}
-EXPORT_SYMBOL(find_task_by_pid_type);
-
/*
* 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
*/
void __init pidhash_init(void)
{
- int i, j, pidhash_size;
+ int i, pidhash_size;
unsigned long megabytes = nr_kernel_pages >> (20 - PAGE_SHIFT);
pidhash_shift = max(4, fls(megabytes * 4));
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]);
- }
+ 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)
/* Reserve PID 0. We never call free_pidmap(0) */
set_bit(0, pidmap_array->page);
atomic_dec(&pidmap_array->nr_free);
+
+ pid_cachep = kmem_cache_create("pid", sizeof(struct pid),
+ __alignof__(struct pid),
+ SLAB_PANIC, NULL, NULL);
}
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