linux-kernel - Re: [PATCH V5 0/9] Fixes for vhost metadata acceleration

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Date:   Thu, 15 Aug 2019 11:28:05 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Christoph Hellwig <hch@...radead.org>,
        Jason Gunthorpe <jgg@...pe.ca>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH V5 0/9] Fixes for vhost metadata acceleration


On 2019/8/14 上午12:41, Christoph Hellwig wrote:
> On Tue, Aug 13, 2019 at 08:57:07AM -0300, Jason Gunthorpe wrote:
>> On Tue, Aug 13, 2019 at 04:31:07PM +0800, Jason Wang wrote:
>>
>>> What kind of issues do you see? Spinlock is to synchronize GUP with MMU
>>> notifier in this series.
>> A GUP that can't sleep can't pagefault which makes it a really weird
>> pattern
> get_user_pages/get_user_pages_fast must not be called under a spinlock.
> We have the somewhat misnamed __get_user_page_fast that just does a
> lookup for existing pages and never faults for a few places that need
> to do that lookup from contexts where we can't sleep.


Yes, I do use __get_user_pages_fast() in the code.

Thanks