Re: [Xen-devel] [PATCH v2] xen/mm: Avoid assuming the page is inuse in assign_pages()

[Jan Beulich <jbeulich@xxxxxxxx>]

On 06.02.2020 11:38, Julien Grall wrote:
> However, the code may race with the page offlining code (see
> offline_page()). Depending on the ordering, the page may be in offlining
> state (PGC_state_offlining) before it is assigned to a domain.
> 
> On debug build, this may result to hit the assert or just clobber the
> state. On non-debug build, the state will get clobbered.
> 
> Incidentally the flag PGC_broken will get clobbered as well.

As mentioned when I first pointed out this issue, it is wider than
just assign_pages() afaict, which is specifically why I said I
wouldn't expect you to want to deal with it alongside the "implicit
inuse" aspect. Fixing just one instance of it without also
addressing the others isn't going to help. IOW you could leave the
code the way it was in v1 in this regard, and then we (you, me, or
yet someone else) take care of the race aspect globally for the
tree.

Jan

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