]> git.proxmox.com Git - mirror_ubuntu-kernels.git/commit
mm/cma.c: remove redundant cma_mutex lock
authorLecopzer Chen <lecopzer.chen@mediatek.com>
Tue, 15 Dec 2020 03:13:23 +0000 (19:13 -0800)
committerLinus Torvalds <torvalds@linux-foundation.org>
Tue, 15 Dec 2020 20:13:46 +0000 (12:13 -0800)
commita4efc174b382fcdb62e2d90d39e78a274a975e38
tree2f5fcc927698c6b47cbac57eaaed34e8dd0907b3
parentd85c6db4cc61bd8299f68534bf7ea2f717f49539
mm/cma.c: remove redundant cma_mutex lock

The cma_mutex which protects alloc_contig_range() was first appeared in
commit 7ee793a62fa8c ("cma: Remove potential deadlock situation"), at that
time, there is no guarantee the behavior of concurrency inside
alloc_contig_range().

After commit 2c7452a075d4db2dc ("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>
mm/cma.c