Re: [RFC PATCH] thunderbolt: do not double dequeue a request

[Mika Westerberg]

Hi,

On Thu, Mar 27, 2025 at 02:52:54PM +0900, Sergey Senozhatsky wrote:
> Some of our devices crash in tb_cfg_request_dequeue():
> 
>  general protection fault, probably for non-canonical address 0xdead000000000122: 0000 [#1] PREEMPT SMP NOPTI
> 
>  CPU: 6 PID: 91007 Comm: kworker/6:2 Tainted: G U W 6.6.65-06391-gbdec63d10750 #1 (HASH:cf42 1)
>  RIP: 0010:tb_cfg_request_dequeue+0x2d/0xa0
>  Call Trace:
>  <TASK>
>  ? tb_cfg_request_dequeue+0x2d/0xa0
>  tb_cfg_request_work+0x33/0x80
>  worker_thread+0x386/0x8f0
>  kthread+0xed/0x110
>  ret_from_fork+0x38/0x50
>  ret_from_fork_asm+0x1b/0x30
> 
> The circumstances are unclear, however, the theory is that
> tb_cfg_request_work() can be scheduled twice for a request:
> first time via frame.callback from ring_work() and second
> time from tb_cfg_request().  Both times kworkers will execute
> tb_cfg_request_dequeue(), which results in double list_del()
> from the ctl->request_queue (the list poison deference hints
> at it: 0xdead000000000122).

I remember seeing similar but it was long time ago.

> Do not dequeue requests that don't have TB_CFG_REQUEST_ACTIVE
> bit set.
> 
> Signed-off-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
> ---
>  drivers/thunderbolt/ctl.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/thunderbolt/ctl.c b/drivers/thunderbolt/ctl.c
> index cd15e84c47f4..3ad15febc7df 100644
> --- a/drivers/thunderbolt/ctl.c
> +++ b/drivers/thunderbolt/ctl.c
> @@ -151,7 +151,12 @@ static void tb_cfg_request_dequeue(struct tb_cfg_request *req)
>  	struct tb_ctl *ctl = req->ctl;
>  
>  	mutex_lock(&ctl->request_queue_lock);
> -	list_del(&req->list);
> +	if (!test_bit(TB_CFG_REQUEST_ACTIVE, &req->flags)) {
> +		mutex_unlock(&ctl->request_queue_lock);
> +		return;
> +	}
> +
> +	list_del_init(&req->list);

Why this change? We are not putting the req back to the list anymore.
Otherwise this looks good to me.

> 
>  	clear_bit(TB_CFG_REQUEST_ACTIVE, &req->flags);
>  	if (test_bit(TB_CFG_REQUEST_CANCELED, &req->flags))
>  		wake_up(&tb_cfg_request_cancel_queue);
> -- 
> 2.49.0.395.g12beb8f557-goog