[net-next v1] net: wwan: t7xx: Fix FSM command timeout issue

[Jinjian Song]

When driver processes the internal state change command, it use
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 te completion notification because the
main thread completion object is 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 ]---

After the main thread determines that the task has timed out, mark
the completion invalid, and add judgment in the asynchronous task.

Signed-off-by: Jinjian Song <jinjian.song at fibocom.com>
---
 drivers/net/wwan/t7xx/t7xx_state_monitor.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wwan/t7xx/t7xx_state_monitor.c b/drivers/net/wwan/t7xx/t7xx_state_monitor.c
index 3931c7a13f5a..57f1a7730fff 100644
--- a/drivers/net/wwan/t7xx/t7xx_state_monitor.c
+++ b/drivers/net/wwan/t7xx/t7xx_state_monitor.c
@@ -108,7 +108,8 @@ static void fsm_finish_command(struct t7xx_fsm_ctl *ctl, struct t7xx_fsm_command
 {
 	if (cmd->flag & FSM_CMD_FLAG_WAIT_FOR_COMPLETION) {
 		*cmd->ret = result;
-		complete_all(cmd->done);
+		if (cmd->done)
+			complete_all(cmd->done);
 	}
 
 	kfree(cmd);
@@ -503,8 +504,10 @@ int t7xx_fsm_append_cmd(struct t7xx_fsm_ctl *ctl, enum t7xx_fsm_cmd_state cmd_id
 
 		wait_ret = wait_for_completion_timeout(&done,
 						       msecs_to_jiffies(FSM_CMD_TIMEOUT_MS));
-		if (!wait_ret)
+		if (!wait_ret) {
+			cmd->done = NULL;
 			return -ETIMEDOUT;
+		}
 
 		return ret;
 	}
-- 
2.34.1