[net-next,v2,1/3] connector/cn_proc: Add hash table for threads

diff --git a/drivers/connector/Makefile b/drivers/connector/Makefile
index 1bf67d3df97d..cb1dcdf067ad 100644
--- a/drivers/connector/Makefile
+++ b/drivers/connector/Makefile
@@ -2,4 +2,4 @@ 
 obj-$(CONFIG_CONNECTOR)		+= cn.o
 obj-$(CONFIG_PROC_EVENTS)	+= cn_proc.o
 
-cn-y				+= cn_queue.o connector.o
+cn-y				+= cn_hash.o cn_queue.o connector.o
diff --git a/drivers/connector/cn_hash.c b/drivers/connector/cn_hash.c
new file mode 100644
index 000000000000..a0211cd99132
--- /dev/null
+++ b/drivers/connector/cn_hash.c
@@ -0,0 +1,195 @@ 
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Author: Anjali Kulkarni <anjali.k.kulkarni@oracle.com>
+ *
+ * Copyright (c) 2024 Oracle and/or its affiliates.
+ */
+
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/connector.h>
+#include <linux/mutex.h>
+#include <linux/pid_namespace.h>
+
+#include <linux/cn_proc.h>
+
+struct cn_hash_dev *cn_hash_alloc_dev(const char *name)
+{
+	struct cn_hash_dev *hdev;
+
+	hdev = kzalloc(sizeof(*hdev), GFP_KERNEL);
+	if (!hdev)
+		return NULL;
+
+	snprintf(hdev->name, sizeof(hdev->name), "%s", name);
+	atomic_set(&hdev->hrefcnt, 0);
+	mutex_init(&hdev->uexit_hash_lock);
+	hash_init(hdev->uexit_pid_htable);
+	return hdev;
+}
+
+void cn_hash_free_dev(struct cn_hash_dev *hdev)
+{
+	struct uexit_pid_hnode *hnode;
+	struct hlist_node *tmp;
+	int bucket;
+
+	pr_debug("%s: Freeing entire hdev %p\n", __func__, hdev);
+
+	mutex_lock(&hdev->uexit_hash_lock);
+	hash_for_each_safe(hdev->uexit_pid_htable, bucket, tmp,
+			hnode, uexit_pid_hlist) {
+		hash_del(&hnode->uexit_pid_hlist);
+		pr_debug("%s: Freeing node for pid %d\n",
+				__func__, hnode->pid);
+		kfree(hnode);
+	}
+
+	mutex_unlock(&hdev->uexit_hash_lock);
+	mutex_destroy(&hdev->uexit_hash_lock);
+
+	while (atomic_read(&hdev->hrefcnt)) {
+		pr_info("Waiting for %s to become free: refcnt=%d\n",
+				hdev->name, atomic_read(&hdev->hrefcnt));
+		msleep(1000);
+	}
+
+	kfree(hdev);
+}
+
+static struct uexit_pid_hnode *cn_hash_alloc_elem(__u32 uexit_code, pid_t pid)
+{
+	struct uexit_pid_hnode *elem;
+
+	elem = kzalloc(sizeof(*elem), GFP_KERNEL);
+	if (!elem)
+		return NULL;
+
+	INIT_HLIST_NODE(&elem->uexit_pid_hlist);
+	elem->uexit_code = uexit_code;
+	elem->pid = pid;
+	return elem;
+}
+
+void cn_hash_free_elem(struct uexit_pid_hnode *elem)
+{
+	kfree(elem);
+}
+
+int cn_hash_add_elem(struct cn_hash_dev *hdev, __u32 uexit_code, pid_t pid)
+{
+	struct uexit_pid_hnode *elem, *hnode;
+
+	elem = cn_hash_alloc_elem(uexit_code, pid);
+	if (!elem) {
+		pr_err("%s: cn_hash_alloc_elem() returned NULL pid %d\n",
+				__func__, pid);
+		return -ENOMEM;
+	}
+
+	mutex_lock(&hdev->uexit_hash_lock);
+	/*
+	 * Check if an entry for the same pid already exists
+	 */
+	hash_for_each_possible(hdev->uexit_pid_htable,
+				hnode, uexit_pid_hlist, pid) {
+		if (hnode->pid == pid) {
+			mutex_unlock(&hdev->uexit_hash_lock);
+			cn_hash_free_elem(elem);
+			pr_debug("%s: pid %d already exists in hash table\n",
+				__func__, pid);
+			return -EEXIST;
+		}
+	}
+
+	hash_add(hdev->uexit_pid_htable, &elem->uexit_pid_hlist, pid);
+	mutex_unlock(&hdev->uexit_hash_lock);
+
+	atomic_inc(&hdev->hrefcnt);
+
+	pr_debug("%s: After hash_add of pid %d elem %p hrefcnt %d\n",
+			__func__, pid, elem, atomic_read(&hdev->hrefcnt));
+	return 0;
+}
+
+int cn_hash_del_elem(struct cn_hash_dev *hdev, pid_t pid)
+{
+	struct uexit_pid_hnode *hnode;
+	struct hlist_node *tmp;
+
+	mutex_lock(&hdev->uexit_hash_lock);
+	hash_for_each_possible_safe(hdev->uexit_pid_htable,
+				hnode, tmp, uexit_pid_hlist, pid) {
+		if (hnode && hnode->pid == pid) {
+			hash_del(&hnode->uexit_pid_hlist);
+			mutex_unlock(&hdev->uexit_hash_lock);
+			kfree(hnode);
+			atomic_dec(&hdev->hrefcnt);
+			pr_debug("%s: After hash_del of pid %d, hrefcnt %d\n",
+					__func__, pid,
+					atomic_read(&hdev->hrefcnt));
+			return 0;
+		}
+	}
+
+	mutex_unlock(&hdev->uexit_hash_lock);
+	pr_err("%s: pid %d not found in hash table\n",
+			__func__, pid);
+	return -EINVAL;
+}
+
+__u32 cn_hash_del_get_exval(struct cn_hash_dev *hdev, pid_t pid)
+{
+	struct uexit_pid_hnode *hnode;
+	struct hlist_node *tmp;
+	__u32 excde;
+
+	mutex_lock(&hdev->uexit_hash_lock);
+	hash_for_each_possible_safe(hdev->uexit_pid_htable,
+				hnode, tmp, uexit_pid_hlist, pid) {
+		if (hnode->pid == pid) {
+			excde = hnode->uexit_code;
+			hash_del(&hnode->uexit_pid_hlist);
+			mutex_unlock(&hdev->uexit_hash_lock);
+			kfree(hnode);
+			atomic_dec(&hdev->hrefcnt);
+			pr_debug("%s: After hash_del of pid %d, found exit code %u hrefcnt %d\n",
+					__func__, pid, excde,
+					atomic_read(&hdev->hrefcnt));
+			return excde;
+		}
+	}
+
+	mutex_unlock(&hdev->uexit_hash_lock);
+	pr_err("%s: pid %d not found in hash table\n",
+			__func__, pid);
+	return 0;
+}
+
+__u32 cn_hash_get_exval(struct cn_hash_dev *hdev, pid_t pid)
+{
+	struct uexit_pid_hnode *hnode;
+	__u32 excde;
+
+	mutex_lock(&hdev->uexit_hash_lock);
+	hash_for_each_possible(hdev->uexit_pid_htable,
+				hnode, uexit_pid_hlist, pid) {
+		if (hnode->pid == pid) {
+			excde = hnode->uexit_code;
+			mutex_unlock(&hdev->uexit_hash_lock);
+			pr_debug("%s: Found exit code %u for pid %d\n",
+					__func__, excde, pid);
+			return excde;
+		}
+	}
+
+	mutex_unlock(&hdev->uexit_hash_lock);
+	pr_debug("%s: pid %d not found in hash table\n",
+			__func__, pid);
+	return -EINVAL;
+}
+
+bool cn_hash_table_empty(struct cn_hash_dev *hdev)
+{
+	return hash_empty(hdev->uexit_pid_htable);
+}
diff --git a/drivers/connector/cn_proc.c b/drivers/connector/cn_proc.c
index 44b19e696176..9205498fcf0f 100644
--- a/drivers/connector/cn_proc.c
+++ b/drivers/connector/cn_proc.c
@@ -69,6 +69,8 @@  static int cn_filter(struct sock *dsk, struct sk_buff *skb, void *data)
 	if ((__u32)val == PROC_EVENT_ALL)
 		return 0;
 
+	pr_debug("%s: val %lx, what %x\n", __func__, val, what);
+
 	/*
 	 * Drop packet if we have to report only non-zero exit status
 	 * (PROC_EVENT_NONZERO_EXIT) and exit status is 0
@@ -326,9 +328,15 @@  void proc_exit_connector(struct task_struct *task)
 	struct proc_event *ev;
 	struct task_struct *parent;
 	__u8 buffer[CN_PROC_MSG_SIZE] __aligned(8);
+	__u32 uexit_code;
 
-	if (atomic_read(&proc_event_num_listeners) < 1)
+	if (atomic_read(&proc_event_num_listeners) < 1) {
+		if (likely(!(task->flags & PF_EXIT_NOTIFY)))
+			return;
+
+		cn_del_elem(task->pid);
 		return;
+	}
 
 	msg = buffer_to_cn_msg(buffer);
 	ev = (struct proc_event *)msg->data;
@@ -337,7 +345,25 @@  void proc_exit_connector(struct task_struct *task)
 	ev->what = PROC_EVENT_EXIT;
 	ev->event_data.exit.process_pid = task->pid;
 	ev->event_data.exit.process_tgid = task->tgid;
-	ev->event_data.exit.exit_code = task->exit_code;
+	if (unlikely(task->flags & PF_EXIT_NOTIFY)) {
+		task->flags &= ~PF_EXIT_NOTIFY;
+
+		uexit_code = cn_del_get_exval(task->pid);
+		if (uexit_code == 0) {
+			pr_debug("%s: Returning with task's exit code %u\n",
+					__func__, task->exit_code);
+			ev->event_data.exit.exit_code = task->exit_code;
+		} else {
+			ev->event_data.exit.exit_code = uexit_code;
+			pr_debug("%s: Reset PF_EXIT_NOTIFY & retrieved exit code %u from hash table, pid %d\n",
+					__func__,
+					ev->event_data.exit.exit_code,
+					task->pid);
+		}
+	} else {
+		ev->event_data.exit.exit_code = task->exit_code;
+	}
+
 	ev->event_data.exit.exit_signal = task->exit_signal;
 
 	rcu_read_lock();
@@ -413,6 +439,13 @@  static void cn_proc_mcast_ctl(struct cn_msg *msg,
 	if (msg->len == sizeof(*pinput)) {
 		pinput = (struct proc_input *)msg->data;
 		mc_op = pinput->mcast_op;
+		if (mc_op == PROC_CN_MCAST_NOTIFY) {
+			pr_debug("%s: Received PROC_CN_MCAST_NOTIFY, pid %d\n",
+					__func__, current->pid);
+			current->flags |= PF_EXIT_NOTIFY;
+			err = cn_add_elem(pinput->uexit_code, current->pid);
+			return;
+		}
 		ev_type = pinput->event_type;
 	} else if (msg->len == sizeof(mc_op)) {
 		mc_op = *((enum proc_cn_mcast_op *)msg->data);
@@ -432,6 +465,8 @@  static void cn_proc_mcast_ctl(struct cn_msg *msg,
 			sk->sk_user_data = kzalloc(sizeof(struct proc_input),
 						   GFP_KERNEL);
 			if (sk->sk_user_data == NULL) {
+				pr_err("%s: ENOMEM for sk_user_data, pid %d\n",
+						__func__, current->pid);
 				err = ENOMEM;
 				goto out;
 			}
@@ -442,21 +477,33 @@  static void cn_proc_mcast_ctl(struct cn_msg *msg,
 		}
 		((struct proc_input *)(sk->sk_user_data))->event_type =
 			ev_type;
+		pr_debug("%s: sk: %p pid: %d event_type: %x\n",
+				__func__, sk, current->pid, ev_type);
 		((struct proc_input *)(sk->sk_user_data))->mcast_op = mc_op;
 	}
 
 	switch (mc_op) {
 	case PROC_CN_MCAST_LISTEN:
-		if (initial || (prev_mc_op != PROC_CN_MCAST_LISTEN))
+		if (initial || (prev_mc_op != PROC_CN_MCAST_LISTEN)) {
 			atomic_inc(&proc_event_num_listeners);
+			pr_debug("%s: PROC_CN_MCAST_LISTEN pid %d: Incremented listeners to %d\n",
+					__func__, current->pid,
+					atomic_read(&proc_event_num_listeners));
+		}
 		break;
 	case PROC_CN_MCAST_IGNORE:
-		if (!initial && (prev_mc_op != PROC_CN_MCAST_IGNORE))
+		if (!initial && (prev_mc_op != PROC_CN_MCAST_IGNORE)) {
 			atomic_dec(&proc_event_num_listeners);
+			pr_debug("%s: PROC_CN_MCAST_IGNORE pid %d: Decremented listeners to %d\n",
+					__func__, current->pid,
+					atomic_read(&proc_event_num_listeners));
+		}
 		((struct proc_input *)(sk->sk_user_data))->event_type =
 			PROC_EVENT_NONE;
 		break;
 	default:
+		pr_warn("%s: Invalid value for mc_op %d\n",
+				__func__, mc_op);
 		err = EINVAL;
 		break;
 	}
diff --git a/drivers/connector/connector.c b/drivers/connector/connector.c
index 4028e8eeba82..506e3cbedf85 100644
--- a/drivers/connector/connector.c
+++ b/drivers/connector/connector.c
@@ -271,6 +271,67 @@  static int __maybe_unused cn_proc_show(struct seq_file *m, void *v)
 	return 0;
 }
 
+__u32 cn_del_get_exval(pid_t pid)
+{
+	struct cn_dev *dev = &cdev;
+	__u32 exval;
+
+	if (!cn_already_initialized)
+		return 0;
+
+	exval = cn_hash_del_get_exval(dev->hdev, pid);
+	return exval;
+}
+EXPORT_SYMBOL_GPL(cn_del_get_exval);
+
+int cn_del_elem(pid_t pid)
+{
+	struct cn_dev *dev = &cdev;
+	int ret;
+
+	if (!cn_already_initialized)
+		return 0;
+
+	ret = cn_hash_del_elem(dev->hdev, pid);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(cn_del_elem);
+
+int cn_add_elem(__u32 uexit_code, pid_t pid)
+{
+	struct cn_dev *dev = &cdev;
+
+	if (!cn_already_initialized)
+		return 0;
+
+	return cn_hash_add_elem(dev->hdev, uexit_code, pid);
+}
+EXPORT_SYMBOL_GPL(cn_add_elem);
+
+__u32 cn_get_exval(pid_t pid)
+{
+	struct cn_dev *dev = &cdev;
+	__u32 exval;
+
+	if (!cn_already_initialized)
+		return 0;
+
+	exval = cn_hash_get_exval(dev->hdev, pid);
+	return exval;
+}
+EXPORT_SYMBOL_GPL(cn_get_exval);
+
+bool cn_table_empty(void)
+{
+	struct cn_dev *dev = &cdev;
+
+	if (!cn_already_initialized)
+		return 0;
+
+	return cn_hash_table_empty(dev->hdev);
+}
+EXPORT_SYMBOL_GPL(cn_table_empty);
+
 static int cn_init(void)
 {
 	struct cn_dev *dev = &cdev;
@@ -283,18 +344,35 @@  static int cn_init(void)
 	};
 
 	dev->nls = netlink_kernel_create(&init_net, NETLINK_CONNECTOR, &cfg);
-	if (!dev->nls)
+	if (!dev->nls) {
+		pr_err("%s: netlink_kernel_create failed, connector not initialized\n",
+				__func__);
 		return -EIO;
+	}
 
 	dev->cbdev = cn_queue_alloc_dev("cqueue", dev->nls);
 	if (!dev->cbdev) {
+		pr_err("%s: Allocation of dev->cbdev failed, connector not initialized\n",
+				__func__);
 		netlink_kernel_release(dev->nls);
 		return -EINVAL;
 	}
 
+	dev->hdev = cn_hash_alloc_dev("pid hash table");
+	if (!dev->hdev) {
+		pr_err("%s: Allocation of dev->hdev failed, connector not initialized\n",
+				__func__);
+		netlink_kernel_release(dev->nls);
+		cn_queue_free_dev(dev->cbdev);
+		return -ENOMEM;
+	}
+
+	pr_debug("Connector initialized, allocated hdev %p\n", dev->hdev);
+
 	cn_already_initialized = 1;
 
-	proc_create_single("connector", S_IRUGO, init_net.proc_net, cn_proc_show);
+	proc_create_single("connector", S_IRUGO, init_net.proc_net,
+				cn_proc_show);
 
 	return 0;
 }
@@ -308,6 +386,7 @@  static void cn_fini(void)
 	remove_proc_entry("connector", init_net.proc_net);
 
 	cn_queue_free_dev(dev->cbdev);
+	cn_hash_free_dev(dev->hdev);
 	netlink_kernel_release(dev->nls);
 }
 
diff --git a/include/linux/connector.h b/include/linux/connector.h
index 70bc1160f3d8..094e1730a4f6 100644
--- a/include/linux/connector.h
+++ b/include/linux/connector.h
@@ -18,6 +18,8 @@ 
 #include <uapi/linux/connector.h>
 
 #define CN_CBQ_NAMELEN		32
+#define HASHT_NAMELEN		32
+#define PID_HASH_TABLE_BITS	10
 
 struct cn_queue_dev {
 	atomic_t refcnt;
@@ -45,6 +47,19 @@  struct cn_callback_entry {
 	u32 seq, group;
 };
 
+struct uexit_pid_hnode {
+	__u32 uexit_code;
+	pid_t pid;
+	struct hlist_node uexit_pid_hlist;
+};
+
+struct cn_hash_dev {
+	atomic_t hrefcnt;
+	unsigned char name[HASHT_NAMELEN];
+	struct mutex uexit_hash_lock;
+	DECLARE_HASHTABLE(uexit_pid_htable, PID_HASH_TABLE_BITS);
+};
+
 struct cn_dev {
 	struct cb_id id;
 
@@ -52,6 +67,7 @@  struct cn_dev {
 	struct sock *nls;
 
 	struct cn_queue_dev *cbdev;
+	struct cn_hash_dev *hdev;
 };
 
 /**
@@ -137,4 +153,31 @@  void cn_queue_free_dev(struct cn_queue_dev *dev);
 
 int cn_cb_equal(const struct cb_id *, const struct cb_id *);
 
+struct cn_hash_dev *cn_hash_alloc_dev(const char *name);
+void cn_hash_free_dev(struct cn_hash_dev *hdev);
+struct uexit_pid_hnode *cn_hash_find_pid_node(struct cn_hash_dev *hdev,
+						pid_t pid);
+void cn_hash_free_elem(struct uexit_pid_hnode *elem);
+int cn_hash_add_elem(struct cn_hash_dev *hdev, __u32 uexit_code, pid_t pid);
+int cn_hash_del_elem(struct cn_hash_dev *hdev, pid_t pid);
+__u32 cn_hash_del_get_exval(struct cn_hash_dev *hdev, pid_t pid);
+
+int cn_add_elem(__u32 uexit_code, pid_t pid);
+int cn_del_elem(pid_t pid);
+__u32 cn_del_get_exval(pid_t pid);
+__u32 cn_get_exval(pid_t pid);
+
+struct cn_hash_dev *cn_hash_alloc_dev(const char *name);
+void cn_hash_free_dev(struct cn_hash_dev *hdev);
+struct uexit_pid_hnode *cn_hash_find_pid_node(struct cn_hash_dev *hdev,
+						pid_t pid);
+void cn_hash_free_elem(struct uexit_pid_hnode *elem);
+int cn_hash_add_elem(struct cn_hash_dev *hdev, __u32 uexit_code, pid_t pid);
+int cn_hash_del_elem(struct cn_hash_dev *hdev, pid_t pid);
+__u32 cn_hash_del_get_exval(struct cn_hash_dev *hdev, pid_t pid);
+__u32 cn_hash_get_exval(struct cn_hash_dev *hdev, pid_t pid);
+
+bool cn_table_empty(void);
+bool cn_hash_table_empty(struct cn_hash_dev *hdev);
+
 #endif				/* __CONNECTOR_H */
diff --git a/include/linux/sched.h b/include/linux/sched.h
index e6ee4258169a..a2339ae6208b 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1673,7 +1673,7 @@  extern struct pid *cad_pid;
 #define PF_USED_MATH		0x00002000	/* If unset the fpu must be initialized before use */
 #define PF_USER_WORKER		0x00004000	/* Kernel thread cloned from userspace thread */
 #define PF_NOFREEZE		0x00008000	/* This thread should not be frozen */
-#define PF__HOLE__00010000	0x00010000
+#define PF_EXIT_NOTIFY		0x00010000	/* This thread has sent an exit value to be sent as a notification to listening processes */
 #define PF_KSWAPD		0x00020000	/* I am kswapd */
 #define PF_MEMALLOC_NOFS	0x00040000	/* All allocations inherit GFP_NOFS. See memalloc_nfs_save() */
 #define PF_MEMALLOC_NOIO	0x00080000	/* All allocations inherit GFP_NOIO. See memalloc_noio_save() */
diff --git a/include/uapi/linux/cn_proc.h b/include/uapi/linux/cn_proc.h
index 18e3745b86cd..2b12a24e4651 100644
--- a/include/uapi/linux/cn_proc.h
+++ b/include/uapi/linux/cn_proc.h
@@ -27,7 +27,8 @@ 
  */
 enum proc_cn_mcast_op {
 	PROC_CN_MCAST_LISTEN = 1,
-	PROC_CN_MCAST_IGNORE = 2
+	PROC_CN_MCAST_IGNORE = 2,
+	PROC_CN_MCAST_NOTIFY = 3
 };
 
 #define PROC_EVENT_ALL (PROC_EVENT_FORK | PROC_EVENT_EXEC | PROC_EVENT_UID |  \
@@ -65,6 +66,7 @@  enum proc_cn_event {
 struct proc_input {
 	enum proc_cn_mcast_op mcast_op;
 	enum proc_cn_event event_type;
+	__u32 uexit_code;
 };
 
 static inline enum proc_cn_event valid_event(enum proc_cn_event ev_type)