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

[Yanjun Zhu <yanjun.zhu@linux.dev>]

在 2022/4/15 14:35, Bob Pearson 写道:
> On 4/15/22 00:54, Yanjun Zhu wrote:
>>
>> 在 2022/4/15 13:37, Bob Pearson 写道:
>>> On 4/15/22 14:56, 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
>>> 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.
>>>
>>> This may be old news.
>>
>> What do you mean? Please check the call trace in the bug.
> 
> I mean the trace you show here shows an instance of xa_lock being
> acquired from the pd pool followed by an instance of xa_lock being
> acquired from rxe_pool_get_index from the ah pool. They are different
> locks. They can't deadlock against each other. So there must be
> some other trace (not shown) that also gets xa_lock from the ah pool.

Please check the bug report mail. The link is 
news://nntp.lore.kernel.org:119/CAHj4cs-MT13RiEsWXUAcX_H5jEtjsebuZgSeUcfptNVuELgjYQ@mail.gmail.com

BTW, what is the update about wr crash caused by your xarray patches?

Zhu Yanjun

> 
>>
>> Zhu Yanjun
>>
>>>
>>>>    </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>
>>>> ---
>>>> 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);
>