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[2603:8081:140c:1a00:447:11e9:73f1:b59c]) by smtp.gmail.com with ESMTPSA id 6-20020aca0706000000b002f9d20b3134sm834704oih.7.2022.04.14.22.37.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 14 Apr 2022 22:37:17 -0700 (PDT) Message-ID: Date: Fri, 15 Apr 2022 00:37:17 -0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.7.0 Subject: Re: [PATCHv4 1/2] RDMA/rxe: Fix a dead lock problem Content-Language: en-US To: yanjun.zhu@linux.dev, jgg@ziepe.ca, leon@kernel.org, linux-rdma@vger.kernel.org References: <20220415195630.279510-1-yanjun.zhu@linux.dev> From: Bob Pearson In-Reply-To: <20220415195630.279510-1-yanjun.zhu@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-rdma@vger.kernel.org On 4/15/22 14:56, yanjun.zhu@linux.dev wrote: > From: Zhu Yanjun > > 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: > > 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. > > > 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] > [ 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 > Signed-off-by: Zhu Yanjun > --- > 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);