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authorEric Biggers <ebiggers@google.com>2017-08-25 15:55:39 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2017-08-25 16:12:46 -0700
commit263630e8d176d87308481ebdcd78ef9426739c6b (patch)
tree83f0e6c1c13076c98b2e22eff4e78c738d9dea5a
parentfffa281b48a91ad6dac1a18c5907ece58fa3879b (diff)
downloadlinux-stericsson-263630e8d176d87308481ebdcd78ef9426739c6b.tar.gz
mm/madvise.c: fix freeing of locked page with MADV_FREE
If madvise(..., MADV_FREE) split a transparent hugepage, it called put_page() before unlock_page(). This was wrong because put_page() can free the page, e.g. if a concurrent madvise(..., MADV_DONTNEED) has removed it from the memory mapping. put_page() then rightfully complained about freeing a locked page. Fix this by moving the unlock_page() before put_page(). This bug was found by syzkaller, which encountered the following splat: BUG: Bad page state in process syzkaller412798 pfn:1bd800 page:ffffea0006f60000 count:0 mapcount:0 mapping: (null) index:0x20a00 flags: 0x200000000040019(locked|uptodate|dirty|swapbacked) raw: 0200000000040019 0000000000000000 0000000000020a00 00000000ffffffff raw: ffffea0006f60020 ffffea0006f60020 0000000000000000 0000000000000000 page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set bad because of flags: 0x1(locked) Modules linked in: CPU: 1 PID: 3037 Comm: syzkaller412798 Not tainted 4.13.0-rc5+ #35 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:16 [inline] dump_stack+0x194/0x257 lib/dump_stack.c:52 bad_page+0x230/0x2b0 mm/page_alloc.c:565 free_pages_check_bad+0x1f0/0x2e0 mm/page_alloc.c:943 free_pages_check mm/page_alloc.c:952 [inline] free_pages_prepare mm/page_alloc.c:1043 [inline] free_pcp_prepare mm/page_alloc.c:1068 [inline] free_hot_cold_page+0x8cf/0x12b0 mm/page_alloc.c:2584 __put_single_page mm/swap.c:79 [inline] __put_page+0xfb/0x160 mm/swap.c:113 put_page include/linux/mm.h:814 [inline] madvise_free_pte_range+0x137a/0x1ec0 mm/madvise.c:371 walk_pmd_range mm/pagewalk.c:50 [inline] walk_pud_range mm/pagewalk.c:108 [inline] walk_p4d_range mm/pagewalk.c:134 [inline] walk_pgd_range mm/pagewalk.c:160 [inline] __walk_page_range+0xc3a/0x1450 mm/pagewalk.c:249 walk_page_range+0x200/0x470 mm/pagewalk.c:326 madvise_free_page_range.isra.9+0x17d/0x230 mm/madvise.c:444 madvise_free_single_vma+0x353/0x580 mm/madvise.c:471 madvise_dontneed_free mm/madvise.c:555 [inline] madvise_vma mm/madvise.c:664 [inline] SYSC_madvise mm/madvise.c:832 [inline] SyS_madvise+0x7d3/0x13c0 mm/madvise.c:760 entry_SYSCALL_64_fastpath+0x1f/0xbe Here is a C reproducer: #define _GNU_SOURCE #include <pthread.h> #include <sys/mman.h> #include <unistd.h> #define MADV_FREE 8 #define PAGE_SIZE 4096 static void *mapping; static const size_t mapping_size = 0x1000000; static void *madvise_thrproc(void *arg) { madvise(mapping, mapping_size, (long)arg); } int main(void) { pthread_t t[2]; for (;;) { mapping = mmap(NULL, mapping_size, PROT_WRITE, MAP_POPULATE|MAP_ANONYMOUS|MAP_PRIVATE, -1, 0); munmap(mapping + mapping_size / 2, PAGE_SIZE); pthread_create(&t[0], 0, madvise_thrproc, (void*)MADV_DONTNEED); pthread_create(&t[1], 0, madvise_thrproc, (void*)MADV_FREE); pthread_join(t[0], NULL); pthread_join(t[1], NULL); munmap(mapping, mapping_size); } } Note: to see the splat, CONFIG_TRANSPARENT_HUGEPAGE=y and CONFIG_DEBUG_VM=y are needed. Google Bug Id: 64696096 Link: http://lkml.kernel.org/r/20170823205235.132061-1-ebiggers3@gmail.com Fixes: 854e9ed09ded ("mm: support madvise(MADV_FREE)") Signed-off-by: Eric Biggers <ebiggers@google.com> Acked-by: David Rientjes <rientjes@google.com> Acked-by: Minchan Kim <minchan@kernel.org> Acked-by: Michal Hocko <mhocko@suse.com> Cc: Dmitry Vyukov <dvyukov@google.com> Cc: Hugh Dickins <hughd@google.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: <stable@vger.kernel.org> [v4.5+] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/madvise.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/mm/madvise.c b/mm/madvise.c
index 47d8d8a25eae..23ed525bc2bc 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -368,8 +368,8 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
pte_offset_map_lock(mm, pmd, addr, &ptl);
goto out;
}
- put_page(page);
unlock_page(page);
+ put_page(page);
pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
pte--;
addr -= PAGE_SIZE;