Re: [PATCH] migration/rdma: prevent from double free the same mr

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* lizhijian@fujitsu.com (lizhijian@fujitsu.com) wrote:
> 
> 
> On 09/07/2021 03:11, Dr. David Alan Gilbert wrote:
> > * Li Zhijian (lizhijian@cn.fujitsu.com) wrote:
> >> backtrace:
> >> '0x00007ffff5f44ec2 in __ibv_dereg_mr_1_1 (mr=0x7fff1007d390) at /home/lizhijian/rdma-core/libibverbs/verbs.c:478
> >> 478             void *addr              = mr->addr;
> > ANy idea why it deletes the same mr twice?
> 
> It's easy to reproduce it if we specify a nvdimm backing to a fsdax memory-backend-file which cannot support registering mr like:
> 
> [root@iaas-rpma ~]# mount | grep pmem0
> /dev/pmem0 on /mnt/pmem0 type ext4 (rw,relatime,seclabel,dax=always)
> 
> [root@iaas-rpma ~]# ndctl list -n namespace0.0
> [
>    {
>      "dev":"namespace0.0",
>      "mode":"fsdax",
>      "map":"mem",
>      "size":536870912,
>      "sector_size":512,
>      "blockdev":"pmem0"
>    }
> ]
> 
> 
> `-object memory-backend-file,id=mem1,share=on,mem-path=/mnt/pmem0/nv-128m.img,size=128m,pmem=on,align=2m -device nvdimm,memdev=mem1,id=nv1`
> 
> and then enable rdma-pin-all.
> 
> (qemu) migrate_set_capability rdma-pin-all on
> (qemu)
> 
> Now qemu has at least 2 ram block, pc.ram and mem1. the latter will be failed to register mr:
> `Failed to register local dest ram block! : Invalid argument   `
> 
> in this case, the mr of pc.ram will be deleted twice.

Ah OK, that makes more sense - from your original description I hadn't
noticed it was the failure path.


Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

> Thanks
> Li
> >
> > Dave
> >
> >> (gdb) bt
> >>   #0  0x00007ffff5f44ec2 in __ibv_dereg_mr_1_1 (mr=0x7fff1007d390) at /home/lizhijian/rdma-core/libibverbs/verbs.c:478
> >>   #1  0x0000555555891fcc in rdma_delete_block (block=<optimized out>, rdma=0x7fff38176010) at ../migration/rdma.c:691
> >>   #2  qemu_rdma_cleanup (rdma=0x7fff38176010) at ../migration/rdma.c:2365
> >>   #3  0x00005555558925b0 in qio_channel_rdma_close_rcu (rcu=0x555556b8b6c0) at ../migration/rdma.c:3073
> >>   #4  0x0000555555d652a3 in call_rcu_thread (opaque=opaque@entry=0x0) at ../util/rcu.c:281
> >>   #5  0x0000555555d5edf9 in qemu_thread_start (args=0x7fffe88bb4d0) at ../util/qemu-thread-posix.c:541
> >>   #6  0x00007ffff54c73f9 in start_thread () at /lib64/libpthread.so.0
> >>   #7  0x00007ffff53f3b03 in clone () at /lib64/libc.so.6 '
> >>
> >> Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
> >> ---
> >>   migration/rdma.c | 1 +
> >>   1 file changed, 1 insertion(+)
> >>
> >> diff --git a/migration/rdma.c b/migration/rdma.c
> >> index b6cc4bef4a8..0f22b8227c0 100644
> >> --- a/migration/rdma.c
> >> +++ b/migration/rdma.c
> >> @@ -1143,6 +1143,7 @@ static int qemu_rdma_reg_whole_ram_blocks(RDMAContext *rdma)
> >>   
> >>       for (i--; i >= 0; i--) {
> >>           ibv_dereg_mr(local->block[i].mr);
> >> +        local->block[i].mr = NULL;
> >>           rdma->total_registrations--;
> >>       }
> >>   
> >> -- 
> >> 2.30.2
> >>
> >>
> >>
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK