Re: [PATCHv3 1/1] RDMA/rxe: Fix a dead lock problem

[Jason Gunthorpe <jgg@ziepe.ca>]

On Wed, Apr 13, 2022 at 03:42:08AM -0400, yanjun.zhu@linux.dev wrote:
> From: Zhu Yanjun <yanjun.zhu@linux.dev>
> 
> This is a dead lock problem.
> The xa_lock first is acquired in this:
> 
> {SOFTIRQ-ON-W} state was registered at:
> 
>   lock_acquire+0x1d2/0x5a0
>   _raw_spin_lock+0x33/0x80
>   __rxe_add_to_pool+0x183/0x230 [rdma_rxe]
>   __ib_alloc_pd+0xf9/0x550 [ib_core]
>   ib_mad_init_device+0x2d9/0xd20 [ib_core]
>   add_client_context+0x2fa/0x450 [ib_core]
>   enable_device_and_get+0x1b7/0x350 [ib_core]
>   ib_register_device+0x757/0xaf0 [ib_core]
>   rxe_register_device+0x2eb/0x390 [rdma_rxe]
>   rxe_net_add+0x83/0xc0 [rdma_rxe]
>   rxe_newlink+0x76/0x90 [rdma_rxe]
>   nldev_newlink+0x245/0x3e0 [ib_core]
>   rdma_nl_rcv_msg+0x2d4/0x790 [ib_core]
>   rdma_nl_rcv+0x1ca/0x3f0 [ib_core]
>   netlink_unicast+0x43b/0x640
>   netlink_sendmsg+0x7eb/0xc40
>   sock_sendmsg+0xe0/0x110
>   __sys_sendto+0x1d7/0x2b0
>   __x64_sys_sendto+0xdd/0x1b0
>   do_syscall_64+0x37/0x80
>   entry_SYSCALL_64_after_hwframe+0x44/0xae
> 
> Then xa_lock is acquired in this:
> 
> {IN-SOFTIRQ-W}:
> 
> Call Trace:
>  <TASK>
>   dump_stack_lvl+0x44/0x57
>   mark_lock.part.52.cold.79+0x3c/0x46
>   __lock_acquire+0x1565/0x34a0
>   lock_acquire+0x1d2/0x5a0
>   _raw_spin_lock_irqsave+0x42/0x90
>   rxe_pool_get_index+0x72/0x1d0 [rdma_rxe]
>   rxe_get_av+0x168/0x2a0 [rdma_rxe]
>   rxe_requester+0x75b/0x4a90 [rdma_rxe]
>   rxe_do_task+0x134/0x230 [rdma_rxe]
>   tasklet_action_common.isra.12+0x1f7/0x2d0
>   __do_softirq+0x1ea/0xa4c
>   run_ksoftirqd+0x32/0x60
>   smpboot_thread_fn+0x503/0x860
>   kthread+0x29b/0x340
>   ret_from_fork+0x1f/0x30
>  </TASK>
> 
> From the above, in the function __rxe_add_to_pool,
> xa_lock is acquired. Then the function __rxe_add_to_pool
> is interrupted by softirq. The function
> rxe_pool_get_index will also acquire xa_lock.
> 
> Finally, the dead lock appears.
> 
> [  296.806097]        CPU0
> [  296.808550]        ----
> [  296.811003]   lock(&xa->xa_lock#15);  <----- __rxe_add_to_pool
> [  296.814583]   <Interrupt>
> [  296.817209]     lock(&xa->xa_lock#15); <---- rxe_pool_get_index
> [  296.820961]
>                  *** DEADLOCK ***
> 
> Fixes: 3225717f6dfa ("RDMA/rxe: Replace red-black trees by carrays")
> Reported-and-tested-by: Yi Zhang <yi.zhang@redhat.com>
> Signed-off-by: Zhu Yanjun <yanjun.zhu@linux.dev>
> ---
> V2->V3: __rxe_add_to_pool is between spin_lock and spin_unlock, so
>         GFP_ATOMIC is used in __rxe_add_to_pool.
> V1->V2: Replace GFP_KERNEL with GFP_ATOMIC
> ---
>  drivers/infiniband/sw/rxe/rxe_pool.c | 17 ++++++++++++-----
>  1 file changed, 12 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/infiniband/sw/rxe/rxe_pool.c b/drivers/infiniband/sw/rxe/rxe_pool.c
> index 87066d04ed18..b9b147df4020 100644
> --- a/drivers/infiniband/sw/rxe/rxe_pool.c
> +++ b/drivers/infiniband/sw/rxe/rxe_pool.c
> @@ -138,8 +138,10 @@ void *rxe_alloc(struct rxe_pool *pool)
>  	elem->obj = obj;
>  	kref_init(&elem->ref_cnt);
>  
> -	err = xa_alloc_cyclic(&pool->xa, &elem->index, elem, pool->limit,
> -			      &pool->next, GFP_KERNEL);
> +	xa_lock_bh(&pool->xa);
> +	err = __xa_alloc_cyclic(&pool->xa, &elem->index, elem, pool->limit,
> +				&pool->next, GFP_KERNEL);
> +	xa_unlock_bh(&pool->xa);
>  	if (err)
>  		goto err_free;

You can't mix bh and not bh locks, either this is an irq spinlock or
it is bh spinlock, pick one and also ensure that the proper xa_init
flag is set.

> @@ -166,8 +168,10 @@ int __rxe_add_to_pool(struct rxe_pool *pool, struct rxe_pool_elem *elem)
>  	elem->obj = (u8 *)elem - pool->elem_offset;
>  	kref_init(&elem->ref_cnt);
>  
> -	err = xa_alloc_cyclic(&pool->xa, &elem->index, elem, pool->limit,
> -			      &pool->next, GFP_KERNEL);
> +	xa_lock_irq(&pool->xa);
> +	err = __xa_alloc_cyclic(&pool->xa, &elem->index, elem, pool->limit,
> +				&pool->next, GFP_ATOMIC);
> +	xa_unlock_irq(&pool->xa);
>  	if (err)
>  		goto err_cnt;

Still no, this does almost every allocation - only AH with the
non-blocking flag set should use this path.

Jason