From a4efc174b382fcdb62e2d90d39e78a274a975e38 Mon Sep 17 00:00:00 2001 From: Lecopzer Chen Date: Mon, 14 Dec 2020 19:13:23 -0800 Subject: [PATCH] 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 Acked-by: David Hildenbrand Acked-by: Vlastimil Babka Cc: Matthias Brugger Cc: YJ Chiang Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/cma.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) diff --git a/mm/cma.c b/mm/cma.c index 7f415d7cda9f..3692a34e2353 100644 --- a/mm/cma.c +++ b/mm/cma.c @@ -38,7 +38,6 @@ struct cma cma_areas[MAX_CMA_AREAS]; unsigned cma_area_count; -static DEFINE_MUTEX(cma_mutex); phys_addr_t cma_get_base(const struct cma *cma) { @@ -454,10 +453,9 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align, mutex_unlock(&cma->lock); pfn = cma->base_pfn + (bitmap_no << cma->order_per_bit); - mutex_lock(&cma_mutex); ret = alloc_contig_range(pfn, pfn + count, MIGRATE_CMA, GFP_KERNEL | (no_warn ? __GFP_NOWARN : 0)); - mutex_unlock(&cma_mutex); + if (ret == 0) { page = pfn_to_page(pfn); break;