Re: [PATCH] vhost: fix deadlock during software live migration of VDPA in a nested virtualization environment

[Hao Chen <chenh@yusur.tech>]

在 2024/1/18 22:46, David Marchand 写道:
> Hello,
> 
> On Thu, Jan 18, 2024 at 11:34 AM Hao Chen <chenh@yusur.tech> wrote:
>>
>> In a nested virtualization environment, running dpdk vdpa in QEMU-L1 for
>> software live migration will result in a deadlock between dpdke-vdpa and
>> QEMU-L2 processes.
>> rte_vdpa_relay_vring_used->
>> __vhost_iova_to_vva->
>> vhost_user_iotlb_rd_unlock(vq)->
>> vhost_user_iotlb_miss-> send vhost message VHOST_USER_SLAVE_IOTLB_MSG to
>> QEMU's vdpa socket,
>> then call vhost_user_iotlb_rd_lock(vq) to hold the read lock `iotlb_lock`.
>> But there is no place to release this read lock.
>>
>> QEMU L2 get the VHOST_USER_SLAVE_IOTLB_MSG,
>> then call vhost_user_send_device_iotlb_msg to send VHOST_USER_IOTLB_MSG
>> messages to dpdk-vdpa.
>> Dpdk vdpa will call vhost_user_iotlb_msg->
>> vhost_user_iotlb_cache_insert, here, will obtain the write lock
>> `iotlb_lock`, but the read lock `iotlb_lock` has not been released and
>> will block here.
>>
>> This patch add lock and unlock function to fix the deadlock.
> 
> Please identify the commit that first had this issue and add a Fixes: tag.
Ok.
> 
>>
>> Signed-off-by: Hao Chen <chenh@yusur.tech>
>> ---
>>   lib/vhost/vdpa.c | 8 +++++++-
>>   1 file changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/lib/vhost/vdpa.c b/lib/vhost/vdpa.c
>> index 9776fc07a9..9132414209 100644
>> --- a/lib/vhost/vdpa.c
>> +++ b/lib/vhost/vdpa.c
>> @@ -19,6 +19,7 @@
>>   #include "rte_vdpa.h"
>>   #include "vdpa_driver.h"
>>   #include "vhost.h"
>> +#include "iotlb.h"
>>
>>   /** Double linked list of vDPA devices. */
>>   TAILQ_HEAD(vdpa_device_list, rte_vdpa_device);
>> @@ -193,10 +194,12 @@ rte_vdpa_relay_vring_used(int vid, uint16_t qid, void *vring_m)
>>                          if (unlikely(nr_descs > vq->size))
>>                                  return -1;
>>
>> +                       vhost_user_iotlb_rd_lock(vq);
>>                          desc_ring = (struct vring_desc *)(uintptr_t)
>>                                  vhost_iova_to_vva(dev, vq,
>>                                                  vq->desc[desc_id].addr, &dlen,
>>                                                  VHOST_ACCESS_RO);
>> +                       vhost_user_iotlb_rd_unlock(vq);
>>                          if (unlikely(!desc_ring))
>>                                  return -1;
>>
>> @@ -220,9 +223,12 @@ rte_vdpa_relay_vring_used(int vid, uint16_t qid, void *vring_m)
>>                          if (unlikely(nr_descs-- == 0))
>>                                  goto fail;
>>                          desc = desc_ring[desc_id];
>> -                       if (desc.flags & VRING_DESC_F_WRITE)
>> +                       if (desc.flags & VRING_DESC_F_WRITE) {
>> +                               vhost_user_iotlb_rd_lock(vq);
>>                                  vhost_log_write_iova(dev, vq, desc.addr,
>>                                                       desc.len);
>> +                               vhost_user_iotlb_rd_unlock(vq);
>> +                       }
>>                          desc_id = desc.next;
>>                  } while (desc.flags & VRING_DESC_F_NEXT);
>>
> 
> Interesting, I suspected a bug in this area as clang was complaining.
> 
> Please try to remove the __rte_no_thread_safety_analysis annotation
> and compile with clang.
> 
> https://git.dpdk.org/dpdk/tree/lib/vhost/vdpa.c#n150
> 
> You will get:
> 
> ccache clang -Ilib/librte_vhost.a.p -Ilib -I../lib -Ilib/vhost
> -I../lib/vhost -I. -I.. -Iconfig -I../config -Ilib/eal/include
> -I../lib/eal/include -Ilib/eal/linux/include
> -I../lib/eal/linux/include -Ilib/eal/x86/include
> -I../lib/eal/x86/include -Ilib/eal/common -I../lib/eal/common
> -Ilib/eal -I../lib/eal -Ilib/kvargs -I../lib/kvargs -Ilib/log
> -I../lib/log -Ilib/metrics -I../lib/metrics -Ilib/telemetry
> -I../lib/telemetry -Ilib/ethdev -I../lib/ethdev -Ilib/net -I../lib/net
> -Ilib/mbuf -I../lib/mbuf -Ilib/mempool -I../lib/mempool -Ilib/ring
> -I../lib/ring -Ilib/meter -I../lib/meter -Ilib/cryptodev
> -I../lib/cryptodev -Ilib/rcu -I../lib/rcu -Ilib/hash -I../lib/hash
> -Ilib/pci -I../lib/pci -Ilib/dmadev -I../lib/dmadev
> -fcolor-diagnostics -fsanitize=address -fno-omit-frame-pointer
> -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -Wextra -Werror -std=c11
> -O0 -g -include rte_config.h -Wcast-qual -Wdeprecated -Wformat
> -Wformat-nonliteral -Wformat-security -Wmissing-declarations
> -Wmissing-prototypes -Wnested-externs -Wold-style-definition
> -Wpointer-arith -Wsign-compare -Wstrict-prototypes -Wundef
> -Wwrite-strings -Wno-address-of-packed-member
> -Wno-missing-field-initializers -D_GNU_SOURCE -fPIC -march=native
> -mrtm -DALLOW_EXPERIMENTAL_API -DALLOW_INTERNAL_API
> -DVHOST_CLANG_UNROLL_PRAGMA -fno-strict-aliasing -DVHOST_HAS_VDUSE
> -DRTE_LOG_DEFAULT_LOGTYPE=lib.vhost -DRTE_ANNOTATE_LOCKS
> -Wthread-safety -MD -MQ lib/librte_vhost.a.p/vhost_vdpa.c.o -MF
> lib/librte_vhost.a.p/vhost_vdpa.c.o.d -o
> lib/librte_vhost.a.p/vhost_vdpa.c.o -c ../lib/vhost/vdpa.c
> ../lib/vhost/vdpa.c:196:5: error: calling function 'vhost_iova_to_vva'
> requires holding mutex 'vq->iotlb_lock'
> [-Werror,-Wthread-safety-analysis]
>                                  vhost_iova_to_vva(dev, vq,
>                                  ^
> ../lib/vhost/vdpa.c:203:13: error: calling function
> 'vhost_alloc_copy_ind_table' requires holding mutex 'vq->iotlb_lock'
> [-Werror,-Wthread-safety-analysis]
>                                  idesc = vhost_alloc_copy_ind_table(dev, vq,
>                                          ^
> ../lib/vhost/vdpa.c:223:5: error: calling function
> 'vhost_log_write_iova' requires holding mutex 'vq->iotlb_lock'
> [-Werror,-Wthread-safety-analysis]
>                                  vhost_log_write_iova(dev, vq, desc.addr,
>                                  ^
> 3 errors generated.
> 
> 
> We may need to protect the vhost_alloc_copy_ind_table() call too.
> What do you think?
Yes, I missed this part. Thank you.
> 
>