Re: [PATCH v5 2/3] mm: migrate: fix barriers around tlb_flush_pending

[Rik van Riel <riel@redhat.com>]

On Mon, 2017-07-31 at 09:43 -0700, Nadav Amit wrote:
> Reading tlb_flush_pending while the page-table lock is taken does not
> require a barrier, since the lock/unlock already acts as a barrier.
> Removing the barrier in mm_tlb_flush_pending() to address this issue.
> 
> However, migrate_misplaced_transhuge_page() calls
> mm_tlb_flush_pending()
> while the page-table lock is already released, which may present a
> problem on architectures with weak memory model (PPC). To deal with
> this
> case, a new parameter is added to mm_tlb_flush_pending() to indicate
> if it is read without the page-table lock taken, and calling
> smp_mb__after_unlock_lock() in this case.
> 
> Cc: Minchan Kim <minchan@kernel.org>
> Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Rik van Riel <riel@redhat.com>
> 
> Signed-off-by: Nadav Amit <namit@vmware.com>
> 
Acked-by: Rik van Riel <riel@redhat.com>

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