Re: [PATCH] mm/x86/pat: Only untrack the pfn range if unmap region

Peter Xu
2024-07-22T21:17:35Z

On Mon, Jul 22, 2024 at 04:22:45PM -0400, Liam R. Howlett wrote:
> The problem report from [2] and [3] is that we are getting to a call
> path that includes unmap_single_vma() without the mmap lock. This patch
> fails to address that issue, it only takes the caller with the assert
> out of the call path.
>
> Removing the function with the lock check doesn't fix the locking issue.
> If there is no locking issue here, please state the case in the commit
> log as you feel it is safe to use a vma pointer without the mmap_lock
> held.

Could you please state why there's a locking issue, and why this patch (of
a x86 PAT specific issue...) would need any documentation on that?

I thought it was pretty common that file truncation (or anything similar)
does a file rmap walk over vmas that mapping this file, and vmas need to be
alive during the rmap walk, no?

Thanks,

--
Peter Xu