On Wed, Aug 23, 2017 at 01:52:35PM -0700, Eric Biggers wrote: > From: Eric Biggers <ebiggers@xxxxxxxxxx> > > 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. > > Fixes: 854e9ed09ded ("mm: support madvise(MADV_FREE)") > Google-Bug-Id: 64696096 > Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> > Cc: Hugh Dickins <hughd@xxxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxxx> > Cc: Minchan Kim <minchan@xxxxxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx # v4.5+ > Acked-by: David Rientjes <rientjes@xxxxxxxxxx> > Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx> Acked-by: Minchan Kim <minchan@xxxxxxxxxx> Thanks!