Commit 73b9ebfe authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
Browse files

[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: default avatarOleg Nesterov <oleg@tv-sign.ru>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent c97d9893

arch/um/kernel/smp.c

+0 −1
Original line number Diff line number Diff line
@@ -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))

include/linux/sched.h

+0 −2
Original line number Diff line number Diff line
@@ -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

kernel/exit.c

+1 −17
Original line number Diff line number Diff line
@@ -56,7 +56,6 @@ 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)--;

	}
@@ -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

kernel/fork.c

+18 −17
Original line number Diff line number Diff line
@@ -1181,6 +1181,7 @@ static task_t *copy_process(unsigned long clone_flags, 
	 */

	p->ioprio = current->ioprio;



	if (likely(p->pid)) {

		add_parent(p);

		if (unlikely(p->ptrace & PT_PTRACED))

			__ptrace_link(p, current->parent);
@@ -1193,13 +1194,13 @@ static task_t *copy_process(unsigned long clone_flags, 
			attach_pid(p, PIDTYPE_SID, p->signal->session);



			list_add_tail(&p->tasks, &init_task.tasks);

		if (p->pid)

			__get_cpu_var(process_counts)++;

		}

		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;

}

kernel/pid.c

+1 −9
Original line number Diff line number Diff line
@@ -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);

}

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