Re: [PATCH] RDMA/rxe: Fix race in do_task() when draining

["yanjun.zhu" <yanjun.zhu@linux.dev>]

On 9/17/25 3:06 AM, Gui-Dong Han wrote:
> When do_task() exhausts its RXE_MAX_ITERATIONS budget, it unconditionally

 From the source code, it will check ret value, then set it to 
TASK_STATE_IDLE, not unconditionally.

> sets the task state to TASK_STATE_IDLE to reschedule. This overwrites
> the TASK_STATE_DRAINING state that may have been concurrently set by
> rxe_cleanup_task() or rxe_disable_task().

 From the source code, there is a spin lock to protect the state. It 
will not make race condition.

> 
> This race condition breaks the cleanup and disable logic, which expects
> the task to stop processing new work. The cleanup code may proceed while
> do_task() reschedules itself, leading to a potential use-after-free.
> 

Can you post the call trace when this problem occurred?

Hi, Jason && Leon

Please comment on this problem.

Thanks a lot.
Yanjun.Zhu

> This bug was introduced during the migration from tasklets to workqueues,
> where the special handling for the draining case was lost.
> 
> Fix this by restoring the original behavior. If the state is
> TASK_STATE_DRAINING when iterations are exhausted, continue the loop by
> setting cont to 1. This allows new iterations to finish the remaining
> work and reach the switch statement, which properly transitions the
> state to TASK_STATE_DRAINED and stops the task as intended.
> 
> Fixes: 9b4b7c1f9f54 ("RDMA/rxe: Add workqueue support for rxe tasks")
> Cc: stable@vger.kernel.org
> Signed-off-by: Gui-Dong Han <hanguidong02@gmail.com>
> ---
>   drivers/infiniband/sw/rxe/rxe_task.c | 8 ++++++--
>   1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/infiniband/sw/rxe/rxe_task.c b/drivers/infiniband/sw/rxe/rxe_task.c
> index 6f8f353e9583..f522820b950c 100644
> --- a/drivers/infiniband/sw/rxe/rxe_task.c
> +++ b/drivers/infiniband/sw/rxe/rxe_task.c
> @@ -132,8 +132,12 @@ static void do_task(struct rxe_task *task)
>   		 * yield the cpu and reschedule the task
>   		 */
>   		if (!ret) {
> -			task->state = TASK_STATE_IDLE;
> -			resched = 1;
> +			if (task->state != TASK_STATE_DRAINING) {
> +				task->state = TASK_STATE_IDLE;
> +				resched = 1;
> +			} else {
> +				cont = 1;
> +			}
>   			goto exit;
>   		}
>