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Tsirkin" , Jason Wang , Xuan Zhuo , Eugenio =?iso-8859-1?Q?P=E9rez?= , Vivek Goyal , Dave Young , Thomas Huth , Cornelia Huck , Janosch Frank , Claudio Imbrenda , Eric Farman , Andrew Morton Subject: Re: [PATCH v1 01/11] fs/proc/vmcore: convert vmcore_cb_lock into vmcore_mutex Message-ID: References: <20241025151134.1275575-1-david@redhat.com> <20241025151134.1275575-2-david@redhat.com> <2b5c2b71-d31b-406d-abc5-d9a0a67712f5@redhat.com> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2b5c2b71-d31b-406d-abc5-d9a0a67712f5@redhat.com> X-Scanned-By: MIMEDefang 3.0 on 10.30.177.15 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. > > Maybe we'd want to backport 1,2,3, but not sure if we consider this critical > enough. > > -- > Cheers, > > David / dhildenb >