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5c3ad2eb71
pageset_update() attempts to update pcplist's high and batch values in a way that readers don't observe batch > high. It uses smp_wmb() to order the updates in a way to achieve this. However, without proper pairing read barriers in readers this guarantee doesn't hold, and there are no such barriers in e.g. free_unref_page_commit(). Commit88e8ac11d2("mm, page_alloc: fix core hung in free_pcppages_bulk()") already showed this is problematic, and solved this by ultimately only trusing pcp->count of the current cpu with interrupts disabled. The update dance with unpaired write barriers thus makes no sense. Replace them with plain WRITE_ONCE to prevent store tearing, and document that the values can change asynchronously and should not be trusted for correctness. All current readers appear to be OK after88e8ac11d2. Convert them to READ_ONCE to prevent unnecessary read tearing, but mainly to alert anybody making future changes to the code that special care is needed. Link: https://lkml.kernel.org/r/20201111092812.11329-5-vbabka@suse.cz Signed-off-by: Vlastimil Babka <vbabka@suse.cz> Reviewed-by: Oscar Salvador <osalvador@suse.de> Acked-by: David Hildenbrand <david@redhat.com> Acked-by: Michal Hocko <mhocko@suse.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
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.