[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>
diff --git a/kernel/pid.c b/kernel/pid.c
index 7781d99..a9f2dfd 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -247,16 +247,8 @@
void __init pidmap_init(void)
{
- int i;
-
pidmap_array->page = (void *)get_zeroed_page(GFP_KERNEL);
+ /* Reserve PID 0. We never call free_pidmap(0) */
set_bit(0, pidmap_array->page);
atomic_dec(&pidmap_array->nr_free);
-
- /*
- * Allocate PID 0, and hash it via all PID types:
- */
-
- for (i = 0; i < PIDTYPE_MAX; i++)
- attach_pid(current, i, 0);
}