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/da90f64c-260a-4329-87bf-1f9ff20a5951@gmail.com/

Fixes: 13e920d93e37 ("net: wwan: t7xx: Add core components")
Signed-off-by: Jinjian Song <jinjian.song@fibocom.com>
Acked-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>
Link: https://patch.msgid.link/20241224041552.8711-1-jinjian.song@fibocom.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/wwan/t7xx/t7xx_state_monitor.c b/drivers/net/wwan/t7xx/t7xx_state_monitor.c
index 3931c7a13f5ab2b732df79055e3a67e0f76cce1d..cbdbb91e8381fcdc32ed0eb42b934311ab2d20c2 100644 (file)
--- a/drivers/net/wwan/t7xx/t7xx_state_monitor.c
+++ b/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;
        }
 

diff --git a/drivers/net/wwan/t7xx/t7xx_state_monitor.h b/drivers/net/wwan/t7xx/t7xx_state_monitor.h
index 7b0a9baf488c1818ab5fc19782f296d81137e5c5..6e0601bb752e51cdfc348e443a91c338964ccb0b 100644 (file)
--- a/drivers/net/wwan/t7xx/t7xx_state_monitor.h
+++ b/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 {