Re: [PATCHv4 1/2] RDMA/rxe: Fix a dead lock problem

Yanjun Zhu <yanjun.zhu@xxxxxxxxx> · Fri, 15 Apr 2022 23:19:50 +0800

在 2022/4/15 13:37, Bob Pearson 写道:
On 4/15/22 14:56, yanjun.zhu@xxxxxxxxx wrote:
From: Zhu Yanjun <yanjun.zhu@xxxxxxxxx>

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

There is a separate xarray for each object pool. So this one is
rxe->pd_pool.xa.xa_lock from rxe_alloc_pd().


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

And this one is rxe->ah_pool.xa.xa_lock from rxe_requester
in the process of sending a UD packet from a work request
which contains the index of the ah.

For your story to work there needs to be an another ah_pool.xa.xa_lock somewhere.
Let's assume it is there somewhere and it's from (a different) add_to_pool call
then the add_to_pool_ routine should disable interrupts when it gets the lock
with spin_lock_xxx. But only for AH objects.

Fortunately, I can reproduce this problem.
"
Apr 15 19:06:05 kernel: rdma_rxe: drivers/infiniband/sw/rxe/rxe_pool.c 
+169, __rxe_add_to_pool, name:ah

Apr 15 19:06:05 kernel: rdma_rxe: drivers/infiniband/sw/rxe/rxe_pool.c 
+189, rxe_pool_get_index, name:ah
"
Please check the above logs. Focus on the pool name.

Zhu Yanjun


This may be old news.

  </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>
---
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);
  	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);








