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The cma_mutex which protects alloc_contig_range() was first appeared in commit7ee793a62f("cma: Remove potential deadlock situation"), at that time, there is no guarantee the behavior of concurrency inside alloc_contig_range(). After commit2c7452a075("mm/page_isolation.c: make start_isolate_page_range() fail if already isolated") > However, two subsystems (CMA and gigantic > huge pages for example) could attempt operations on the same range. If > this happens, one thread may 'undo' the work another thread is doing. > This can result in pageblocks being incorrectly left marked as > MIGRATE_ISOLATE and therefore not available for page allocation. The concurrency inside alloc_contig_range() was clarified. Now we can find that hugepage and virtio call alloc_contig_range() without any lock, thus cma_mutex is "redundant" in cma_alloc() now. Link: https://lkml.kernel.org/r/20201020102241.3729-1-lecopzer.chen@mediatek.com Signed-off-by: Lecopzer Chen <lecopzer.chen@mediatek.com> Acked-by: David Hildenbrand <david@redhat.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Matthias Brugger <matthias.bgg@gmail.com> Cc: YJ Chiang <yj.chiang@mediatek.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.