linux-kernel - Re: [PATCH v9 5/6] vduse: add vq group asid support

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Message-ID: <20251119042923-mutt-send-email-mst@kernel.org>
Date: Wed, 19 Nov 2025 04:32:20 -0500
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Eugenio Perez Martin <eperezma@...hat.com>
Cc: Jason Wang <jasowang@...hat.com>, Laurent Vivier <lvivier@...hat.com>,
	virtualization@...ts.linux.dev,
	Maxime Coquelin <mcoqueli@...hat.com>, Cindy Lu <lulu@...hat.com>,
	linux-kernel@...r.kernel.org, Yongji Xie <xieyongji@...edance.com>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	Stefano Garzarella <sgarzare@...hat.com>
Subject: Re: [PATCH v9 5/6] vduse: add vq group asid support

On Wed, Nov 19, 2025 at 10:26:43AM +0100, Eugenio Perez Martin wrote:
> > But this is not the logic that is
> > implemented in this patch as there's no synchronize_rcu() in the
> > vduse_set_group_asid_nomsg().
> 
> We only set the pointer on the writer's side, we do nothing like
> freeing resources. Should we set the pointer before or after
> syncrhonize_rcu()?

synchronize_rcu is called after writer makes it's changes.

> What do we need to do on the other side of
> syncrhonize_rcu()?

Presumably, return so the caller knows the as has been updated.

However, user-triggerable synchronize_rcu() is almost always a bug.

If that's what is going on, you want srcu.


-- 
MST