]> git.baikalelectronics.ru Git - kernel.git/commit
mm/filemap: fix filemap_map_pages for THP
authorMatthew Wilcox (Oracle) <willy@infradead.org>
Tue, 13 Oct 2020 23:51:44 +0000 (16:51 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Wed, 14 Oct 2020 01:38:29 +0000 (18:38 -0700)
commit79d9ecfe128b5d6c623bd6b621ce75ea4cbca031
treeb962741062e1d757a4793b3834b43283c1d3b5c4
parent41d5660a09a47de4474857ac09695056b47c50a6
mm/filemap: fix filemap_map_pages for THP

We dereference page->mapping and page->index directly after calling
find_subpage() and these fields are not valid for tail pages.  While
commit e86f80c4c247 ("mm: page cache: store only head pages in i_pages")
introduced the call to find_subpage(), the problem existed prior to this;
I'm going to suggest all the way back to when THPs first existed.

The user-visible effects of this are almost negligible.  To hit it, you
have to mmap a tmpfs file at an unaligned address and then it's only a
disabled optimisation causing page faults to happen more frequently than
they otherwise would.

Fix this by keeping both head and page pointers and checking the
appropriate one.  We could use page_mapping() and page_to_index(), but
that's higher overhead.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: William Kucharski <william.kucharski@oracle.com>
Link: https://lkml.kernel.org/r/20200911012532.24761-1-willy@infradead.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/filemap.c