4 files changed, 22 insertions, 0 deletions

diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index f0e52383a001..1516a8ff8f92 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -41,6 +41,7 @@ extern struct fs_struct init_fs;
 
 #define INIT_SIGNALS(sig) {                                             \
         .nr_threads     = 1,                                            \
+        .thread_head    = LIST_HEAD_INIT(init_task.thread_node),        \
         .wait_chldexit  = __WAIT_QUEUE_HEAD_INITIALIZER(sig.wait_chldexit),\
         .shared_pending = {                                             \
                 .list = LIST_HEAD_INIT(sig.shared_pending.list),        \
@@ -222,6 +223,7 @@ extern struct task_group root_task_group;
                 [PIDTYPE_SID]  = INIT_PID_LINK(PIDTYPE_SID),            \
         },                                                              \
         .thread_group   = LIST_HEAD_INIT(tsk.thread_group),             \
+        .thread_node    = LIST_HEAD_INIT(init_signals.thread_head),     \
         INIT_IDS                                                        \
         INIT_PERF_EVENTS(tsk)                                           \
         INIT_TRACE_IRQFLAGS                                             \
diff --git a/include/linux/sched.h b/include/linux/sched.h
index ffccdad050b5..485234d2fd42 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -549,6 +549,7 @@ struct signal_struct {
         atomic_t                sigcnt;
         atomic_t                live;
         int                     nr_threads;
+        struct list_head        thread_head;
 
         wait_queue_head_t       wait_chldexit;  /* for wait4() */
 
@@ -1271,6 +1272,7 @@ struct task_struct {
         /* PID/PID hash table linkage. */
         struct pid_link pids[PIDTYPE_MAX];
         struct list_head thread_group;
+        struct list_head thread_node;
 
         struct completion *vfork_done;          /* for vfork() */
         int __user *set_child_tid;              /* CLONE_CHILD_SETTID */
@@ -2341,6 +2343,16 @@ extern bool current_is_single_threaded(void);
 #define while_each_thread(g, t) \
         while ((t = next_thread(t)) != g)
 
+#define __for_each_thread(signal, t)    \
+        list_for_each_entry_rcu(t, &(signal)->thread_head, thread_node)
+
+#define for_each_thread(p, t)           \
+        __for_each_thread((p)->signal, t)
+
+/* Careful: this is a double loop, 'break' won't work as expected. */
+#define for_each_process_thread(p, t)   \
+        for_each_process(p) for_each_thread(p, t)
+
 static inline int get_nr_threads(struct task_struct *tsk)
 {
         return tsk->signal->nr_threads;
diff --git a/kernel/exit.c b/kernel/exit.c
index a949819055d5..1e77fc645317 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -74,6 +74,7 @@ static void __unhash_process(struct task_struct *p, bool group_dead)
                 __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 294189fc7ac8..2f11bbe376b0 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1035,6 +1035,11 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
         sig->nr_threads = 1;
         atomic_set(&sig->live, 1);
         atomic_set(&sig->sigcnt, 1);
+
+        /* list_add(thread_node, thread_head) without INIT_LIST_HEAD() */
+        sig->thread_head = (struct list_head)LIST_HEAD_INIT(tsk->thread_node);
+        tsk->thread_node = (struct list_head)LIST_HEAD_INIT(sig->thread_head);
+
         init_waitqueue_head(&sig->wait_chldexit);
         sig->curr_target = tsk;
         init_sigpending(&sig->shared_pending);
@@ -1474,6 +1479,8 @@ static struct task_struct *copy_process(unsigned long clone_flags,
                         atomic_inc(&current->signal->sigcnt);
                         list_add_tail_rcu(&p->thread_group,
                                           &p->group_leader->thread_group);
+                        list_add_tail_rcu(&p->thread_node,
+                                          &p->signal->thread_head);
                 }
                 attach_pid(p, PIDTYPE_PID);
                 nr_threads++;