On 12/8/21 2:34 PM, Michael S. Tsirkin wrote:

On Mon, Nov 29, 2021 at 01:46:57PM -0600, Mike Christie wrote:

quoted

The following patches made over Linus's tree, allow the vhost layer to do
a copy_process on the thread that does the VHOST_SET_OWNER ioctl like how
io_uring does a copy_process against its userspace app. This allows the
vhost layer's worker threads to inherit cgroups, namespaces, address
space, etc and this worker thread will also be accounted for against that
owner/parent process's RLIMIT_NPROC limit.

If you are not familiar with qemu and vhost here is more detailed
problem description:

Qemu will create vhost devices in the kernel which perform network, SCSI,
etc IO and management operations from worker threads created by the
kthread API. Because the kthread API does a copy_process on the kthreadd
thread, the vhost layer has to use kthread_use_mm to access the Qemu
thread's memory and cgroup_attach_task_all to add itself to the Qemu
thread's cgroups.

The problem with this approach is that we then have to add new functions/
args/functionality for every thing we want to inherit. I started doing
that here:

https://urldefense.com/v3/__https://lkml.org/lkml/2021/6/23/1233__;!!ACWV5N9M2RV99hQ!ceUHd4m4MTJFOGccB9N5r7WonxVoYYT2XPiYwWt2-Vt1Y-DmQirRN8OqKozFLN1h73N6$ 

for the RLIMIT_NPROC check, but it seems it might be easier to just
inherit everything from the beginning, becuase I'd need to do something
like that patch several times.

So who's merging this? Me? Did all patches get acked by appropriate
maintainers?

Not yet.

Jens, The last open review comment was from you for the name change
and additional patch description info.

In this posting, I changed the name from:

kernel_worker/kernel_worker_start

to

user_worker_create/user_worker_start

I didn't do the start/create_user_worker format originally discussed
because a while back Christoph had given me a review comment about trying
to tie everything together into an API. Everything having the user_worker
prefix felt nicer in that it was easy to tell the functions and flags went
together, and so I thought it would handle his comment too.

And patch:

[PATCH V6 07/10] io_uring: switch to user_worker

should better explain the reason for the switch.
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