linux-kernel - Re: [PATCH v1 01/11] fs/proc/vmcore: convert vmcore_cb_lock into vmcore

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Message-ID: <1ca5ae5e-4b92-418c-a73c-2c736e5b93d3@redhat.com>
Date: Wed, 20 Nov 2024 09:56:41 +0100
From: David Hildenbrand <david@...hat.com>
To: Baoquan He <bhe@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 linux-s390@...r.kernel.org, virtualization@...ts.linux.dev,
 kvm@...r.kernel.org, linux-fsdevel@...r.kernel.org,
 kexec@...ts.infradead.org, Heiko Carstens <hca@...ux.ibm.com>,
 Vasily Gorbik <gor@...ux.ibm.com>, Alexander Gordeev
 <agordeev@...ux.ibm.com>, Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Sven Schnelle <svens@...ux.ibm.com>, "Michael S. Tsirkin" <mst@...hat.com>,
 Jason Wang <jasowang@...hat.com>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
 Eugenio Pérez <eperezma@...hat.com>,
 Vivek Goyal <vgoyal@...hat.com>, Dave Young <dyoung@...hat.com>,
 Thomas Huth <thuth@...hat.com>, Cornelia Huck <cohuck@...hat.com>,
 Janosch Frank <frankja@...ux.ibm.com>,
 Claudio Imbrenda <imbrenda@...ux.ibm.com>, Eric Farman
 <farman@...ux.ibm.com>, Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v1 01/11] fs/proc/vmcore: convert vmcore_cb_lock into
 vmcore_mutex

On 20.11.24 09:16, Baoquan He wrote:
> On 11/15/24 at 11:03am, David Hildenbrand wrote:
>> On 15.11.24 10:30, Baoquan He wrote:
>>> On 10/25/24 at 05:11pm, David Hildenbrand wrote:
>>>> We want to protect vmcore modifications from concurrent opening of
>>>> the vmcore, and also serialize vmcore modiciations. Let's convert the
>>>
>>>
>>>> spinlock into a mutex, because some of the operations we'll be
>>>> protecting might sleep (e.g., memory allocations) and might take a bit
>>>> longer.
>>>
>>> Could you elaborate this a little further. E.g the concurrent opening of
>>> vmcore is spot before this patchset or have been seen, and in which place
>>> the memory allocation is spot. Asking this becasue I'd like to learn and
>>> make clear if this is a existing issue and need be back ported into our
>>> old RHEL distros. Thanks in advance.
>>
>> It's a preparation for the other patches, that do what is described here:
>>
>> a) We can currently modify the vmcore after it was opened. This can happen
>> if the vmcoredd is added after the vmcore was loaded. Similar things will
>> happen with the PROC_VMCORE_DEVICE_RAM extension.
>>
>> b) To handle it cleanly we need to protect the modifications against
>> concurrent opening. And the modifcations end up allocating memory and cannot
>> easily take the spinlock.
>>
>> So far a spinlock was sufficient, now a mutex is required.
> 
> I see, as we talked in patch 2 sub-thread, these information are very
> valuable to help people get the background information when they read
> code. Let's put it in patch log. Thanks.

I'll extend the description if that helps, thanks!

-- 
Cheers,

David / dhildenb