Re: [PATCH] migration/rdma: Fix cm_event used before being initialized

[address@hidden]

On 14/05/2021 01.15, Dr. David Alan Gilbert wrote:
> * Li Zhijian (lizhijian@cn.fujitsu.com) wrote:
>> A segmentation fault was triggered when i try to abort a postcopy + rdma
>> migration.
>>
>> since rdma_ack_cm_event releases a uninitialized cm_event in thise case.
>>
>> like below:
>> 2496     ret = rdma_get_cm_event(rdma->channel, &cm_event);
>> 2497     if (ret) {
>> 2498         perror("rdma_get_cm_event after rdma_connect");
>> 2499         ERROR(errp, "connecting to destination!");
>> 2500         rdma_ack_cm_event(cm_event); <<<< cause segmentation fault
>> 2501         goto err_rdma_source_connect;
>> 2502     }
>>
>> Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
> OK, that's an easy fix then; but I wonder if we should perhaps remove
> that rdma_ack_cm_event, if it's the get_cm_event that's failed?

I also wondered, i checked the man page get_cm_event(3) which has not documented

and checked some rdma examples, some of them try to ack it[1],  but some not[2].

[1]: 
https://github.com/linux-rdma/rdma-core/blob/e381334c2915a5290565694947790d4aebaf2222/librdmacm/examples/mckey.c#L451
[2]: 
https://github.com/linux-rdma/rdma-core/blob/e381334c2915a5290565694947790d4aebaf2222/librdmacm/examples/mckey.c#L342

Thanks

>
> Still,
>
>
> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
>
>> ---
>>   migration/rdma.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/migration/rdma.c b/migration/rdma.c
>> index 00eac34232..2dadb62aed 100644
>> --- a/migration/rdma.c
>> +++ b/migration/rdma.c
>> @@ -2466,7 +2466,7 @@ static int qemu_rdma_connect(RDMAContext *rdma, Error 
>> **errp)
>>                                             .private_data = &cap,
>>                                             .private_data_len = sizeof(cap),
>>                                           };
>> -    struct rdma_cm_event *cm_event;
>> +    struct rdma_cm_event *cm_event = NULL;
>>       int ret;
>>   
>>       /*
>> -- 
>> 2.30.2
>>
>>
>>