[PATCH] pidhash: don't count idle threads

fork_idle() does unhash_process() just after copy_process().  Contrary,
boot_cpu's idle thread explicitely registers itself for each pid_type with nr
= 0.

copy_process() already checks p->pid != 0 before process_counts++, I think we
can just skip attach_pid() calls and job control inits for idle threads and
kill unhash_process().  We don't need to cleanup ->proc_dentry in fork_idle()
because with this patch idle threads are never hashed in
kernel/pid.c:pid_hash[].

We don't need to hash pid == 0 in pidmap_init().  free_pidmap() is never
called with pid == 0 arg, so it will never be reused.  So it is still possible
to use pid == 0 in any PIDTYPE_xxx namespace from kernel/pid.c's POV.

However with this patch we don't hash pid == 0 for PIDTYPE_PID case.  We still
have have PIDTYPE_PGID/PIDTYPE_SID entries with pid == 0: /sbin/init and
kernel threads which don't call daemonize().

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 1 insertions, 17 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index f436a6b..a94e1c3 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -56,8 +56,7 @@ static void __unhash_process(struct task_struct *p)
 		detach_pid(p, PIDTYPE_SID);
 
 		list_del_init(&p->tasks);
-		if (p->pid)
-			__get_cpu_var(process_counts)--;
+		__get_cpu_var(process_counts)--;
 	}
 
 	remove_parent(p);
@@ -118,21 +117,6 @@ repeat:
 		goto repeat;
 }
 
-/* we are using it only for SMP init */
-
-void unhash_process(struct task_struct *p)
-{
-	struct dentry *proc_dentry;
-
-	spin_lock(&p->proc_lock);
-	proc_dentry = proc_pid_unhash(p);
-	write_lock_irq(&tasklist_lock);
-	__unhash_process(p);
-	write_unlock_irq(&tasklist_lock);
-	spin_unlock(&p->proc_lock);
-	proc_pid_flush(proc_dentry);
-}
-
 /*
  * This checks not only the pgrp, but falls back on the pid if no
  * satisfactory pgrp is found. I dunno - gdb doesn't work correctly