[PATCH] fixed pidhashing patch

This patch fixes strange and obscure pid implementation in current kernels:
- it removes calling of put_task_struct() from detach_pid()
  under tasklist_lock. This allows to use blocking calls
  in security_task_free() hooks (in __put_task_struct()).
- it saves some space = 5*5 ints = 100 bytes in task_struct
- it's smaller and tidy, more straigthforward and doesn't use
  any knowledge about pids using and assignment.
- it removes pid_links and pid_struct doesn't hold reference counters
  on task_struct. instead, new pid_structs and linked altogether and
  only one of them is inserted in hash_list.

Signed-off-by: Kirill Korotaev (kksx@mail.ru)
Signed-off-by: William Irwin <wli@holomorphy.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 21 insertions, 32 deletions

diff --git a/include/linux/pid.h b/include/linux/pid.h
index 02fb2d216d2b..5f74c4ab0d11 100644
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -12,35 +12,22 @@ enum pid_type
 
 struct pid
 {
-	/* Try to keep hash_chain in the same cacheline as nr for find_pid */
-	struct hlist_node hash_chain;
+	/* Try to keep pid_chain in the same cacheline as nr for find_pid */
 	int nr;
-	atomic_t count;
-	struct task_struct *task;
-	struct list_head task_list;
-};
-
-struct pid_link
-{
-	struct list_head pid_chain;
-	struct pid *pidptr;
-	struct pid pid;
+	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;
 };
 
 #define pid_task(elem, type) \
-	list_entry(elem, struct task_struct, pids[type].pid_chain)
+	list_entry(elem, struct task_struct, pids[type].pid_list)
 
 /*
- * attach_pid() and link_pid() must be called with the tasklist_lock
+ * 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 void FASTCALL(link_pid(struct task_struct *task, struct pid_link *link, struct pid *pid));
-
-/*
- * detach_pid() must be called with the tasklist_lock write-held.
- */
 extern void FASTCALL(detach_pid(struct task_struct *task, enum pid_type));
 
 /*
@@ -53,13 +40,16 @@ extern int alloc_pidmap(void);
 extern void FASTCALL(free_pidmap(int));
 extern void switch_exec_pids(struct task_struct *leader, struct task_struct *thread);
 
-#define for_each_task_pid(who, type, task, elem, pid)		\
-	if ((pid = find_pid(type, who)))			\
-	        for (elem = pid->task_list.next,			\
-			prefetch(elem->next),				\
-			task = pid_task(elem, type);			\
-			elem != &pid->task_list;			\
-			elem = elem->next, prefetch(elem->next), 	\
-			task = pid_task(elem, type))
+#define do_each_task_pid(who, type, task)				\
+	if ((task = find_task_by_pid_type(type, who))) {		\
+		prefetch((task)->pids[type].pid_list.next);		\
+		do {
+
+#define while_each_task_pid(who, type, task)				\
+			task = pid_task((task)->pids[type].pid_list.next,\
+						type);			\
+			prefetch((task)->pids[type].pid_list.next);	\
+		} while (hlist_unhashed(&(task)->pids[type].pid_chain));\
+	}								\
 
 #endif /* _LINUX_PID_H */
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 3aaf8e5f2216..5cf33f072140 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -494,7 +494,7 @@ struct task_struct {
 	struct task_struct *group_leader;	/* threadgroup leader */
 
 	/* PID/PID hash table linkage. */
-	struct pid_link pids[PIDTYPE_MAX];
+	struct pid pids[PIDTYPE_MAX];
 
 	wait_queue_head_t wait_chldexit;	/* for wait4() */
 	struct completion *vfork_done;		/* for vfork() */
@@ -673,7 +673,8 @@ extern struct task_struct init_task;
 
 extern struct   mm_struct init_mm;
 
-extern struct task_struct *find_task_by_pid(int pid);
+#define find_task_by_pid(nr)	find_task_by_pid_type(PIDTYPE_PID, nr)
+extern struct task_struct *find_task_by_pid_type(int type, int pid);
 extern void set_special_pids(pid_t session, pid_t pgrp);
 extern void __set_special_pids(pid_t session, pid_t pgrp);
 
@@ -876,9 +877,7 @@ extern task_t * FASTCALL(next_thread(const task_t *p));
 
 static inline int thread_group_empty(task_t *p)
 {
-	struct pid *pid = p->pids[PIDTYPE_TGID].pidptr;
-
-	return pid->task_list.next->next == &pid->task_list;
+	return list_empty(&p->pids[PIDTYPE_TGID].pid_list);
 }
 
 #define delay_group_leader(p) \