net: wwan: t7xx: Fix FSM command timeout issue

When driver processes the internal state change command, it use an
asynchronous thread to process the command operation. If the main
thread detects that the task has timed out, the asynchronous thread
will panic when executing the completion notification because the
main thread completion object has been released.

BUG: unable to handle page fault for address: fffffffffffffff8
PGD 1f283a067 P4D 1f283a067 PUD 1f283c067 PMD 0
Oops: 0000 [#1] PREEMPT SMP NOPTI
RIP: 0010:complete_all+0x3e/0xa0
[...]
Call Trace:
 <TASK>
 ? __die_body+0x68/0xb0
 ? page_fault_oops+0x379/0x3e0
 ? exc_page_fault+0x69/0xa0
 ? asm_exc_page_fault+0x22/0x30
 ? complete_all+0x3e/0xa0
 fsm_main_thread+0xa3/0x9c0 [mtk_t7xx (HASH:1400 5)]
 ? __pfx_autoremove_wake_function+0x10/0x10
 kthread+0xd8/0x110
 ? __pfx_fsm_main_thread+0x10/0x10 [mtk_t7xx (HASH:1400 5)]
 ? __pfx_kthread+0x10/0x10
 ret_from_fork+0x38/0x50
 ? __pfx_kthread+0x10/0x10
 ret_from_fork_asm+0x1b/0x30
 </TASK>
[...]
CR2: fffffffffffffff8
---[ end trace 0000000000000000 ]---

Use the reference counter to ensure safe release as Sergey suggests:
https://lore.kernel.org/all/[email protected]/

Fixes: 13e920d ("net: wwan: t7xx: Add core components")
Signed-off-by: Jinjian Song <[email protected]>
Acked-by: Sergey Ryazanov <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: Jinjian-Song

drivers/net/wwan/t7xx/t7xx_state_monitor.c

@@ -104,14 +104,21 @@ void t7xx_fsm_broadcast_state(struct t7xx_fsm_ctl *ctl, enum md_state state)
 	fsm_state_notify(ctl->md, state);
 }
 
+static void fsm_release_command(struct kref *ref)
+{
+	struct t7xx_fsm_command *cmd = container_of(ref, typeof(*cmd), refcnt);
+
+	kfree(cmd);
+}
+
 static void fsm_finish_command(struct t7xx_fsm_ctl *ctl, struct t7xx_fsm_command *cmd, int result)
 {
 	if (cmd->flag & FSM_CMD_FLAG_WAIT_FOR_COMPLETION) {
-		*cmd->ret = result;
-		complete_all(cmd->done);
+		cmd->result = result;
+		complete_all(&cmd->done);
 	}
 
-	kfree(cmd);
+	kref_put(&cmd->refcnt, fsm_release_command);
 }
 
 static void fsm_del_kf_event(struct t7xx_fsm_event *event)
@@ -475,7 +482,6 @@ static int fsm_main_thread(void *data)
 
 int t7xx_fsm_append_cmd(struct t7xx_fsm_ctl *ctl, enum t7xx_fsm_cmd_state cmd_id, unsigned int flag)
 {
-	DECLARE_COMPLETION_ONSTACK(done);
 	struct t7xx_fsm_command *cmd;
 	unsigned long flags;
 	int ret;
@@ -487,11 +493,13 @@ int t7xx_fsm_append_cmd(struct t7xx_fsm_ctl *ctl, enum t7xx_fsm_cmd_state cmd_id
 	INIT_LIST_HEAD(&cmd->entry);
 	cmd->cmd_id = cmd_id;
 	cmd->flag = flag;
+	kref_init(&cmd->refcnt);
 	if (flag & FSM_CMD_FLAG_WAIT_FOR_COMPLETION) {
-		cmd->done = &done;
-		cmd->ret = &ret;
+		init_completion(&cmd->done);
+		kref_get(&cmd->refcnt);
 	}
 
+	kref_get(&cmd->refcnt);
 	spin_lock_irqsave(&ctl->command_lock, flags);
 	list_add_tail(&cmd->entry, &ctl->command_queue);
 	spin_unlock_irqrestore(&ctl->command_lock, flags);
@@ -501,11 +509,11 @@ int t7xx_fsm_append_cmd(struct t7xx_fsm_ctl *ctl, enum t7xx_fsm_cmd_state cmd_id
 	if (flag & FSM_CMD_FLAG_WAIT_FOR_COMPLETION) {
 		unsigned long wait_ret;
 
-		wait_ret = wait_for_completion_timeout(&done,
+		wait_ret = wait_for_completion_timeout(&cmd->done,
 						       msecs_to_jiffies(FSM_CMD_TIMEOUT_MS));
-		if (!wait_ret)
-			return -ETIMEDOUT;
 
+		ret = wait_ret ? cmd->result : -ETIMEDOUT;
+		kref_put(&cmd->refcnt, fsm_release_command);
 		return ret;
 	}
 

drivers/net/wwan/t7xx/t7xx_state_monitor.h

@@ -110,8 +110,9 @@ struct t7xx_fsm_command {
 	struct list_head	entry;
 	enum t7xx_fsm_cmd_state	cmd_id;
 	unsigned int		flag;
-	struct completion	*done;
-	int			*ret;
+	struct completion	done;
+	int			result;
+	struct kref		refcnt;
 };
 
 struct t7xx_fsm_notifier {