在 2022/4/21 0:32, Jason Gunthorpe 写道:
On Wed, Apr 20, 2022 at 09:42:23AM +0300, Leon Romanovsky wrote:
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
+++ 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);
It should just use xa_alloc_cyclic_irq() and xa_erase_irq(). Don't
open code the lock.
Got it. I will use the above functions.
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?
The spinlock type needs to be consistent in all users.
You can only use the naked version if the spinlock is always obtained
from a process context.
You can only use bh version if the spinlock is always obtained from a
process context or bh/softirq
You can always use the irq version
What I don't understand is why IRQ and not BH? AFAIK there is no case
where rxe is called from a real IRQ, right? Or is it because you can't
nest BH under the IRQ spinlock from CM?
Sure. I will use IRQ spinlock. The reason is as below:
1.
https://patchwork.kernel.org/project/linux-rdma/patch/20220210073655.42281-2-guoqing.jiang@xxxxxxxxx/
2.
https://patchwork.kernel.org/project/linux-rdma/patch/20220215194448.44369-1-rpearsonhpe@xxxxxxxxx/
The above 2 links are why I used IRQ.
Zhu Yanjun
Jason
