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authorMatthew Wilcox (Oracle) <willy@infradead.org>2020-10-14 02:56:04 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2020-10-14 04:38:33 +0300
commite320d3012d25b1fb5f3df4edb7bd44a1c362ec10 (patch)
tree045231cbb1f31c38cbb22189a08d284398fc09ae /mm/page_alloc.c
parenta9b576f7253e22528584f5aeb46edf0b6b007992 (diff)
downloadlinux-e320d3012d25b1fb5f3df4edb7bd44a1c362ec10.tar.xz
mm/page_alloc.c: fix freeing non-compound pages
Here is a very rare race which leaks memory: Page P0 is allocated to the page cache. Page P1 is free. Thread A Thread B Thread C find_get_entry(): xas_load() returns P0 Removes P0 from page cache P0 finds its buddy P1 alloc_pages(GFP_KERNEL, 1) returns P0 P0 has refcount 1 page_cache_get_speculative(P0) P0 has refcount 2 __free_pages(P0) P0 has refcount 1 put_page(P0) P1 is not freed Fix this by freeing all the pages in __free_pages() that won't be freed by the call to put_page(). It's usually not a good idea to split a page, but this is a very unlikely scenario. Fixes: e286781d5f2e ("mm: speculative page references") Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Acked-by: Mike Rapoport <rppt@linux.ibm.com> Cc: Nick Piggin <npiggin@gmail.com> Cc: Hugh Dickins <hughd@google.com> Cc: Peter Zijlstra <peterz@infradead.org> Link: https://lkml.kernel.org/r/20200926213919.26642-1-willy@infradead.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/page_alloc.c')
-rw-r--r--mm/page_alloc.c3
1 files changed, 3 insertions, 0 deletions
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 6263a97e39c6..73e33ab6d249 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4952,6 +4952,9 @@ void __free_pages(struct page *page, unsigned int order)
{
if (put_page_testzero(page))
free_the_page(page, order);
+ else if (!PageHead(page))
+ while (order-- > 0)
+ free_the_page(page + (1 << order), order);
}
EXPORT_SYMBOL(__free_pages);