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[PATCH] pidhash: don't count idle threads

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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>
This commit is contained in:
Oleg Nesterov 2006-03-28 16:11:07 -08:00 • committed by Linus Torvalds
parent c97d98931a
commit 73b9ebfe12
5 changed files with 18 additions and 44 deletions
Download patch file Download diff file Expand all files Collapse all files

18
kernel/exit.c
View file

@ -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