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mm: move call to compound_head() in release_pages()

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The function is_huge_zero_page() doesn't call compound_head() to make sure
the page pointer is a head page. The call to is_huge_zero_page() in
release_pages() is made before compound_head() is called so the test would
fail if release_pages() was called with a tail page of the huge_zero_page
and put_page_testzero() would be called releasing the page.
This is unlikely to be happening in normal use or we would be seeing all
sorts of process data corruption when accessing a THP zero page.

Looking at other places where is_huge_zero_page() is called, all seem to
only pass a head page so I think the right solution is to move the call
to compound_head() in release_pages() to a point before calling
is_huge_zero_page().

Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Christoph Hellwig <hch@lst.de>
Link: https://lkml.kernel.org/r/20200917173938.16420-1-rcampbell@nvidia.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Ralph Campbell 2020-10-13 16:56:00 -07:00 committed by Linus Torvalds
parent 30d8ec73e8
commit a9b576f725
1 changed files with 1 additions and 1 deletions
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2
mm/swap.c
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@ -889,6 +889,7 @@ void release_pages(struct page **pages, int nr)
locked_pgdat = NULL;
}
page = compound_head(page);
if (is_huge_zero_page(page))
continue;
@ -910,7 +911,6 @@ void release_pages(struct page **pages, int nr)
}
}
page = compound_head(page);
if (!put_page_testzero(page))
continue;