Re: [PATCH] RDMA/rxe: Fix race condition in QP timer handlers

[Leon Romanovsky <leon@kernel.org>]

On Tue, Jan 20, 2026 at 03:44:37PM +0800, Li Zhijian wrote:
> I encontered the following warning:
>  WARNING: drivers/infiniband/sw/rxe/rxe_task.c:249 at rxe_sched_task+0x1c8/0x238 [rdma_rxe], CPU#0: swapper/0/0
> ...
>   libsha1 [last unloaded: ip6_udp_tunnel]
>  CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Tainted: G         C          6.19.0-rc5-64k-v8+ #37 PREEMPT
>  Tainted: [C]=CRAP
>  Hardware name: Raspberry Pi 4 Model B Rev 1.2
>  Call trace:
>   rxe_sched_task+0x1c8/0x238 [rdma_rxe] (P)
>   retransmit_timer+0x130/0x188 [rdma_rxe]
>   call_timer_fn+0x68/0x4d0
>   __run_timers+0x630/0x888
> ...
>  WARNING: drivers/infiniband/sw/rxe/rxe_task.c:38 at rxe_sched_task+0x1c0/0x238 [rdma_rxe], CPU#0: swapper/0/0
> ...
>  WARNING: drivers/infiniband/sw/rxe/rxe_task.c:111 at do_work+0x488/0x5c8 [rdma_rxe], CPU#3: kworker/u17:4/93400
> ...
>  refcount_t: underflow; use-after-free.
>  WARNING: lib/refcount.c:28 at refcount_warn_saturate+0x138/0x1a0, CPU#3: kworker/u17:4/93400
> 
> The issue is caused by a race condition between retransmit_timer() and
> rxe_destroy_qp, leading to the Queue Pair's (QP) reference count dropping
> to zero during timer handler execution.
> 
> It seems this warning is harmless because rxe_qp_do_cleanup() will flush
> all pending timers and requests.
> 
> Example of flow causing the issue:
> 
> CPU0                                   CPU1
> retransmit_timer() {
>     spin_lock_irqsave
>                            rxe_destroy_qp()
>                             __rxe_cleanup()
>                               __rxe_put() // qp->ref_count decrease to 0
>                             rxe_qp_do_cleanup() {
>     if (qp->valid) {
>         rxe_sched_task() {
>             WARN_ON(rxe_read(task->qp) <= 0);
>         }
>     }
>     spin_unlock_irqrestore
> }
>                               spin_lock_irqsave
>                               qp->valid = 0
>                               spin_unlock_irqrestore
>                             }
> 
> Ensure the QP's reference count is maintained and its validity is checked
> within the timer callbacks by adding calls to rxe_get(qp) and corresponding
> rxe_put(qp) after use.
> 
> Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>

Fixes line?

Thanks

> ---
>  drivers/infiniband/sw/rxe/rxe_comp.c | 3 +++
>  drivers/infiniband/sw/rxe/rxe_req.c  | 3 +++
>  2 files changed, 6 insertions(+)