[PATCH] proc: Rewrite the proc dentry flush on exit optimization

To keep the dcache from filling up with dead /proc entries we flush them on
process exit.  However over the years that code has gotten hairy with a
dentry_pointer and a lock in task_struct and misdocumented as a correctness
feature.

I have rewritten this code to look and see if we have a corresponding entry in
the dcache and if so flush it on process exit.  This removes the extra fields
in the task_struct and allows me to trivially handle the case of a
/proc/<tgid>/task/<pid> entry as well as the current /proc/<pid> entries.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

kernel/exit.c

@@ -137,12 +137,8 @@ void release_task(struct task_struct * p)
 {
 	int zap_leader;
 	task_t *leader;
-	struct dentry *proc_dentry;
-
 repeat:
 	atomic_dec(&p->user->processes);
-	spin_lock(&p->proc_lock);
-	proc_dentry = proc_pid_unhash(p);
 	write_lock_irq(&tasklist_lock);
 	ptrace_unlink(p);
 	BUG_ON(!list_empty(&p->ptrace_list) || !list_empty(&p->ptrace_children));
@@ -171,8 +167,7 @@ repeat:
 
 	sched_exit(p);
 	write_unlock_irq(&tasklist_lock);
-	spin_unlock(&p->proc_lock);
-	proc_pid_flush(proc_dentry);
+	proc_flush_task(p);
 	release_thread(p);
 	call_rcu(&p->rcu, delayed_put_task_struct);
 

kernel/fork.c

@@ -993,13 +993,10 @@ static task_t *copy_process(unsigned long clone_flags,
 		if (put_user(p->pid, parent_tidptr))
 			goto bad_fork_cleanup;
 
-	p->proc_dentry = NULL;
-
 	INIT_LIST_HEAD(&p->children);
 	INIT_LIST_HEAD(&p->sibling);
 	p->vfork_done = NULL;
 	spin_lock_init(&p->alloc_lock);
-	spin_lock_init(&p->proc_lock);
 
 	clear_tsk_thread_flag(p, TIF_SIGPENDING);
 	init_sigpending(&p->pending);