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Re: [PATCH] console: generalize the ability for domU access
- To: "Daniel P. Smith" <dpsmith@xxxxxxxxxxxxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Fri, 4 Aug 2023 09:49:53 +0200
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- Cc: Christopher Clark <christopher.w.clark@xxxxxxxxx>, Luca Fancellu <luca.fancellu@xxxxxxx>, Henry Wang <Henry.Wang@xxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Stefano Stabellini <stefano.stabellini@xxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Fri, 04 Aug 2023 07:50:07 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 03.08.2023 18:31, Daniel P. Smith wrote:
> On 8/3/23 11:56, Jan Beulich wrote:
>> On 03.08.2023 14:56, Daniel P. Smith wrote:
>>> On 8/2/23 07:01, Jan Beulich wrote:
>>>> On 01.08.2023 18:06, Daniel P. Smith wrote:
>>>>> + {
>>>>> + for_each_domain(next)
>>>>
>>>> What guarantees that the list won't change behind your back? You don't
>>>> hold domlist_read_lock here afaict. It might be that you're safe because
>>>> that lock is an RCU one and this function is only invoked at init time
>>>> or from some form of interrupt handler. But that's far from obvious and
>>>> will hence need both properly confirming and stating in a comment. (It
>>>> is actually this concern, iirc, which so far had us avoid iterating the
>>>> domain list here.)
>>>
>>> It is better to error on the side of caution instead of assuming this
>>> will always be invoked in a safe manner. I will add a read lock for the
>>> domain list.
>>
>> I'm not firm enough in RCU to be certain whether acquiring that lock is
>> permissible here.
>
> Same and I took your statements to suggest that I should.
Actually I wasn't paying close enough attention here: The code already
uses rcu_lock_domain_by_id(), which acquires domlist_read_lock.
Jan
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