From 18c830df771f2ba8b4699fea9af1492275ae627b Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Wed, 3 Jul 2013 15:08:32 -0700 Subject: [PATCH] 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: Oleg Nesterov Cc: "Eric W. Biederman" Cc: Michal Hocko Cc: Pavel Emelyanov Cc: Sergey Dyasly Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/fork.c | 33 ++++++++++++++++----------------- 1 file changed, 16 insertions(+), 17 deletions(-) diff --git a/kernel/fork.c b/kernel/fork.c index 7d6962fb6156..6e6a1c11b3e5 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -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->exit_signal = current->group_leader->exit_signal; - else - p->exit_signal = (clone_flags & CSIGNAL); + 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(¤t->signal->live); atomic_inc(¤t->signal->sigcnt); - p->group_leader = current->group_leader; list_add_tail_rcu(&p->thread_group, &p->group_leader->thread_group); } -- 2.20.1