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Re: [PATCH v9 02/16] vpci: use per-domain PCI lock to protect vpci structure
- To: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- From: Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
- Date: Mon, 25 Sep 2023 23:03:29 +0000
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Stewart Hildebrand <stewart.hildebrand@xxxxxxx>, Oleksandr Andrushchenko <Oleksandr_Andrushchenko@xxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Jun Nakajima <jun.nakajima@xxxxxxxxx>, Kevin Tian <kevin.tian@xxxxxxxxx>, Paul Durrant <paul@xxxxxxx>
- Delivery-date: Mon, 25 Sep 2023 23:04:19 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Thread-index: AQHZ2s9KfUsugiaE80OWAJ/SuT82fLAiaWIAgAnmCQA=
- Thread-topic: [PATCH v9 02/16] vpci: use per-domain PCI lock to protect vpci structure
Hi Roger,
Roger Pau Monné <roger.pau@xxxxxxxxxx> writes:
> On Tue, Aug 29, 2023 at 11:19:42PM +0000, Volodymyr Babchuk wrote:
>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
>>
>> Use a previously introduced per-domain read/write lock to check
>> whether vpci is present, so we are sure there are no accesses to the
>> contents of the vpci struct if not. This lock can be used (and in a
>> few cases is used right away) so that vpci removal can be performed
>> while holding the lock in write mode. Previously such removal could
>> race with vpci_read for example.
>>
>> When taking both d->pci_lock and pdev->vpci->lock they are should be
>
> When taking both d->pci_lock and pdev->vpci->lock the order should be
> ...
>
>> taken in this exact order: d->pci_lock then pdev->vpci->lock to avoid
>> possible deadlock situations.
>>
Will it be better to write like this:
"When taking both d->pci_lock and pdev->vpci->lock, they should be
taken in this exact order: d->pci_lock then pdev->vpci->lock to avoid
possible deadlock situations."
?
I am asking because your suggestion leads to "When taking both
d->pci_lock and pdev->vpci->lock the order should be taken in this exact
order: ... "
[...]
As for other comments, I am taking into account your, Jan's and Stewart's
comments and reworking this patch.
--
WBR, Volodymyr
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