Re: [Xen-devel] [PATCH]fix hang on migration

[Zhigang Wang <zhigang.x.wang@xxxxxxxxxx>]

Hi Keir,

The hang happens often when you runs many VM simultaneously. So I'd like
this patch go to 3.4-testing as well.

This is the regenerated patch against xen-3.4-testing.

Signed-off-by: Zhigang Wang <zhigang.x.wang@xxxxxxxxxx>
Reviewed-by: Xiaowei Hu <xiaowei.hu@xxxxxxxxxx>

thanks,

zhigang

Zhigang Wang wrote:
> hi,
> 
> the migration process may be hang when you start another VM while the 
> migration is under way.
> 
> Eg.
> 
> Start a VM:
> 
> # xm create OVM_EL5U3_X86_PVHVM_4GB/vm.cfg
> 
> Wait for the VM bootup, then start another VM while this VM is migration:
> 
> # xm migrate -l OVM_EL5U3_X86_PVHVM_4GB localhost &
> # xm create OVM_EL5U1_X86_HVM_4GB/vm.cfg
> 
> The migration will hang on:
> 
> # xm list
> Name                                        ID   Mem VCPUs      State   
> Time(s)
> Domain-0                                     0   543     2     r-----    110.1
> OVM_EL5U1_X86_HVM_4GB                        4   256     1     -b----     39.6
> OVM_EL5U3_X86_PVHVM_4GB                      5   512     1     --p---      0.0
> 
> The migration will only finish after shutting down VM OVM_EL5U1_X86_HVM_4GB.
> 
> This is because we are using a threaded model in xend, and the migration 
> thread is running
> in the same context, and we are using pipes/sockets in migration.
> 
> So the write side of the pipe/socket created while migration will inherited 
> to children, thus
> the reading side of the pipe/socket will hang if there is a child forked and 
> the child never end up
> (like qemu-dm).
> 
> So we should close all inherited open file descriptors in every forked 
> process.
> 
> Ian: please review the patch against qemu-dm forking.
> 
> Signed-off-by: Zhigang Wang <zhigang.x.wang@xxxxxxxxxx>
> Reviewed-by: Xiaowei Hu <xiaowei.hu@xxxxxxxxxx>
> 
> thanks,
> 
> zhigang
> 
> 
> 
> 
> 
> 
> ------------------------------------------------------------------------
> 
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