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Commit 18c830df authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
Browse files

kernel/fork.c:copy_process(): consolidate the lockless CLONE_THREAD checks 



copy_process() does a lot of "chaotic" initializations and checks
CLONE_THREAD twice before it takes tasklist.  In particular it sets
"p->group_leader = p" and then changes it again under tasklist if
!thread_group_leader(p).

This looks a bit confusing, lets create a single "if (CLONE_THREAD)" block
which initializes ->exit_signal, ->group_leader, and ->tgid.

Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Sergey Dyasly <dserrg@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 81907739

kernel/fork.c

+16 −17
Original line number Diff line number Diff line
@@ -1360,11 +1360,6 @@ static struct task_struct *copy_process(unsigned long clone_flags, 
			goto bad_fork_cleanup_io;

	}



	p->pid = pid_nr(pid);

	p->tgid = p->pid;

	if (clone_flags & CLONE_THREAD)

		p->tgid = current->tgid;



	p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? child_tidptr : NULL;

	/*

	 * Clear TID on mm_release()?
@@ -1400,12 +1395,19 @@ static struct task_struct *copy_process(unsigned long clone_flags, 
	clear_all_latency_tracing(p);



	/* ok, now we should be set up.. */

	if (clone_flags & CLONE_THREAD)

	p->pid = pid_nr(pid);

	if (clone_flags & CLONE_THREAD) {

		p->exit_signal = -1;

	else if (clone_flags & CLONE_PARENT)

		p->group_leader = current->group_leader;

		p->tgid = current->tgid;

	} else {

		if (clone_flags & CLONE_PARENT)

			p->exit_signal = current->group_leader->exit_signal;

		else

			p->exit_signal = (clone_flags & CSIGNAL);

		p->group_leader = p;

		p->tgid = p->pid;

	}



	p->pdeath_signal = 0;

	p->exit_state = 0;
@@ -1414,15 +1416,13 @@ static struct task_struct *copy_process(unsigned long clone_flags, 
	p->nr_dirtied_pause = 128 >> (PAGE_SHIFT - 10);

	p->dirty_paused_when = 0;



	/*

	 * Ok, make it visible to the rest of the system.

	 * We dont wake it up yet.

	 */

	p->group_leader = p;

	INIT_LIST_HEAD(&p->thread_group);

	p->task_works = NULL;



	/* Need tasklist lock for parent etc handling! */

	/*

	 * Make it visible to the rest of the system, but dont wake it up yet.

	 * Need tasklist lock for parent etc handling!

	 */

	write_lock_irq(&tasklist_lock);



	/* CLONE_PARENT re-uses the old parent */
@@ -1476,7 +1476,6 @@ static struct task_struct *copy_process(unsigned long clone_flags, 
			current->signal->nr_threads++;

			atomic_inc(&current->signal->live);

			atomic_inc(&current->signal->sigcnt);

			p->group_leader = current->group_leader;

			list_add_tail_rcu(&p->thread_group,

					  &p->group_leader->thread_group);

		}