[PATCH 0/2] kill task_struct->thread_group

[PATCH 0/2] kill task_struct->thread_group

[Oleg Nesterov]

On top of

	[PATCH 0/2] introduce __next_thread(), change next_thread()
	https://lore.kernel.org/all/20230824143112.GA31208@redhat.com/

Next: audit the while_each_thread() users.

Oleg.

[PATCH 1/2] change thread_group_empty() to use task_struct->thread_node

[Oleg Nesterov]

It could use list_is_singular() but this way it is cheaper. Plus the
thread_group_leader() check makes it clear that thread_group_empty()
can only return true if p is a group leader. This was not immediately
obvious before this patch.

task_struct->thread_group no longer has users, it can die.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 include/linux/sched/signal.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index cffc882d367f..d7fa3ca2fa53 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -733,7 +733,8 @@ static inline struct task_struct *next_thread(struct task_struct *p)
 
 static inline int thread_group_empty(struct task_struct *p)
 {
-	return list_empty(&p->thread_group);
+	return thread_group_leader(p) &&
+	       list_is_last(&p->thread_node, &p->signal->thread_head);
 }
 
 #define delay_group_leader(p) \
-- 
2.25.1.362.g51ebf55

[PATCH 2/2] kill task_struct->thread_group

[Oleg Nesterov]

The last user was removed by the previous patch.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 include/linux/sched.h | 1 -
 init/init_task.c      | 1 -
 kernel/exit.c         | 1 -
 kernel/fork.c         | 3 ---
 4 files changed, 6 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 609bde814cb0..2b012d446cad 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -997,7 +997,6 @@ struct task_struct {
 	/* PID/PID hash table linkage. */
 	struct pid			*thread_pid;
 	struct hlist_node		pid_links[PIDTYPE_MAX];
-	struct list_head		thread_group;
 	struct list_head		thread_node;
 
 	struct completion		*vfork_done;
diff --git a/init/init_task.c b/init/init_task.c
index ff6c4b9bfe6b..c0de0200fd56 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -132,7 +132,6 @@ struct task_struct init_task
 	.pi_lock	= __RAW_SPIN_LOCK_UNLOCKED(init_task.pi_lock),
 	.timer_slack_ns = 50000, /* 50 usec default slack */
 	.thread_pid	= &init_struct_pid,
-	.thread_group	= LIST_HEAD_INIT(init_task.thread_group),
 	.thread_node	= LIST_HEAD_INIT(init_signals.thread_head),
 #ifdef CONFIG_AUDIT
 	.loginuid	= INVALID_UID,
diff --git a/kernel/exit.c b/kernel/exit.c
index edb50b4c9972..f3ba4b97a7d9 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -133,7 +133,6 @@ static void __unhash_process(struct task_struct *p, bool group_dead)
 		list_del_init(&p->sibling);
 		__this_cpu_dec(process_counts);
 	}
-	list_del_rcu(&p->thread_group);
 	list_del_rcu(&p->thread_node);
 }
 
diff --git a/kernel/fork.c b/kernel/fork.c
index d2e12b6d2b18..3cd6913a90ef 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2579,7 +2579,6 @@ __latent_entropy struct task_struct *copy_process(
 	p->dirty_paused_when = 0;
 
 	p->pdeath_signal = 0;
-	INIT_LIST_HEAD(&p->thread_group);
 	p->task_works = NULL;
 	clear_posix_cputimers_work(p);
 
@@ -2707,8 +2706,6 @@ __latent_entropy struct task_struct *copy_process(
 			atomic_inc(&current->signal->live);
 			refcount_inc(&current->signal->sigcnt);
 			task_join_group_stop(p);
-			list_add_tail_rcu(&p->thread_group,
-					  &p->group_leader->thread_group);
 			list_add_tail_rcu(&p->thread_node,
 					  &p->signal->thread_head);
 		}
-- 
2.25.1.362.g51ebf55