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page_ref_freeze and page_ref_unfreeze are designed to be used as a pair, wrapping a critical section where struct pages can be modified without having to worry about consistency for a concurrent fast-GUP. Whilst page_ref_freeze has full barrier semantics due to its use of atomic_cmpxchg, page_ref_unfreeze is implemented using atomic_set, which doesn't provide any barrier semantics and allows the operation to be reordered with respect to page modifications in the critical section. This patch ensures that page_ref_unfreeze is ordered after any critical section updates, by invoking smp_mb() prior to the atomic_set. Link: http://lkml.kernel.org/r/1497349722-6731-3-git-send-email-will.deacon@arm.com Signed-off-by: Will Deacon <will.deacon@arm.com> Acked-by: Steve Capper <steve.capper@arm.com> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.