On Sat, Apr 16, 2022 at 10:43:42PM -0400, yanjun.zhu@xxxxxxxxx wrote:
> From: Zhu Yanjun <yanjun.zhu@xxxxxxxxx>
>
> This is a dead lock problem.
> The ah_pool 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]
>
> Then ah_pool 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]
> </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@xxxxxxxxxx>
> Signed-off-by: Zhu Yanjun <yanjun.zhu@xxxxxxxxx>
> ---
> V4->V5: Commit logs are changed to avoid confusion.
> V3->V4: xa_lock_irq locks are used.
> 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 | 20 ++++++++++++++------
> 1 file changed, 14 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/infiniband/sw/rxe/rxe_pool.c b/drivers/infiniband/sw/rxe/rxe_pool.c
> index 87066d04ed18..f1f06dc7e64f 100644
> --- a/drivers/infiniband/sw/rxe/rxe_pool.c
> +++ b/drivers/infiniband/sw/rxe/rxe_pool.c
> @@ -106,7 +106,7 @@ void rxe_pool_init(struct rxe_dev *rxe, struct rxe_pool *pool,
>
> atomic_set(&pool->num_elem, 0);
>
> - xa_init_flags(&pool->xa, XA_FLAGS_ALLOC);
> + xa_init_flags(&pool->xa, XA_FLAGS_ALLOC | XA_FLAGS_LOCK_IRQ);
> pool->limit.min = info->min_index;
> pool->limit.max = info->max_index;
> }
> @@ -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_irq(&pool->xa);
> + err = __xa_alloc_cyclic(&pool->xa, &elem->index, elem, pool->limit,
> + &pool->next, GFP_KERNEL);
> + xa_unlock_irq(&pool->xa);
I may admit that I didn't follow your previous discussions, so maybe you
already explained it. But why do you need xa_lock_irq() here?
Thanks
> if (err)
> goto err_free;
>
> @@ -155,6 +157,7 @@ void *rxe_alloc(struct rxe_pool *pool)
> int __rxe_add_to_pool(struct rxe_pool *pool, struct rxe_pool_elem *elem)
> {
> int err;
> + unsigned long flags;
>
> if (WARN_ON(pool->flags & RXE_POOL_ALLOC))
> return -EINVAL;
> @@ -166,8 +169,10 @@ 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_irqsave(&pool->xa, flags);
> + err = __xa_alloc_cyclic(&pool->xa, &elem->index, elem, pool->limit,
> + &pool->next, GFP_ATOMIC);
> + xa_unlock_irqrestore(&pool->xa, flags);
> if (err)
> goto err_cnt;
>
> @@ -200,8 +205,11 @@ static void rxe_elem_release(struct kref *kref)
> {
> struct rxe_pool_elem *elem = container_of(kref, typeof(*elem), ref_cnt);
> struct rxe_pool *pool = elem->pool;
> + unsigned long flags;
>
> - xa_erase(&pool->xa, elem->index);
> + xa_lock_irqsave(&pool->xa, flags);
> + __xa_erase(&pool->xa, elem->index);
> + xa_unlock_irqrestore(&pool->xa, flags);
>
> if (pool->cleanup)
> pool->cleanup(elem);
> --
> 2.27.0
>
