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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
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1
arch/um/kernel/smp.c
View File

@ -143,7 +143,6 @@ void smp_prepare_cpus(unsigned int maxcpus)
idle = idle_thread(cpu);
init_idle(idle, cpu);
unhash_process(idle);
waittime = 200000000;
while (waittime-- && !cpu_isset(cpu, cpu_callin_map))

2
include/linux/sched.h
View File

@ -1214,8 +1214,6 @@ static inline int thread_group_empty(task_t *p)
#define delay_group_leader(p) \
(thread_group_leader(p) && !thread_group_empty(p))
extern void unhash_process(struct task_struct *p);
/*
* Protects ->fs, ->files, ->mm, ->ptrace, ->group_info, ->comm, keyring
* subscriptions and synchronises with wait4(). Also used in procfs. Also

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 @@ void release_task(struct task_struct * p)
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

31
kernel/fork.c
View File

@ -1181,25 +1181,26 @@ static task_t *copy_process(unsigned long clone_flags,
*/
p->ioprio = current->ioprio;
add_parent(p);
if (unlikely(p->ptrace & PT_PTRACED))
__ptrace_link(p, current->parent);
if (likely(p->pid)) {
add_parent(p);
if (unlikely(p->ptrace & PT_PTRACED))
__ptrace_link(p, current->parent);
if (thread_group_leader(p)) {
p->signal->tty = current->signal->tty;
p->signal->pgrp = process_group(current);
p->signal->session = current->signal->session;
attach_pid(p, PIDTYPE_PGID, process_group(p));
attach_pid(p, PIDTYPE_SID, p->signal->session);
if (thread_group_leader(p)) {
p->signal->tty = current->signal->tty;
p->signal->pgrp = process_group(current);
p->signal->session = current->signal->session;
attach_pid(p, PIDTYPE_PGID, process_group(p));
attach_pid(p, PIDTYPE_SID, p->signal->session);
list_add_tail(&p->tasks, &init_task.tasks);
if (p->pid)
list_add_tail(&p->tasks, &init_task.tasks);
__get_cpu_var(process_counts)++;
}
attach_pid(p, PIDTYPE_TGID, p->tgid);
attach_pid(p, PIDTYPE_PID, p->pid);
nr_threads++;
}
attach_pid(p, PIDTYPE_TGID, p->tgid);
attach_pid(p, PIDTYPE_PID, p->pid);
nr_threads++;
total_forks++;
spin_unlock(&current->sighand->siglock);
write_unlock_irq(&tasklist_lock);
@ -1263,7 +1264,7 @@ task_t * __devinit fork_idle(int cpu)
if (!task)
return ERR_PTR(-ENOMEM);
init_idle(task, cpu);
unhash_process(task);
return task;
}

10
kernel/pid.c
View File

@ -247,16 +247,8 @@ void __init pidhash_init(void)
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);
}