mm: fix locking order in mm_take_all_locks()

Dmitry Vyukov has reported[1] possible deadlock (triggered by his
syzkaller fuzzer):

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&hugetlbfs_i_mmap_rwsem_key);
                               lock(&mapping->i_mmap_rwsem);
                               lock(&hugetlbfs_i_mmap_rwsem_key);
  lock(&mapping->i_mmap_rwsem);

Both traces points to mm_take_all_locks() as a source of the problem.
It doesn't take care about ordering or hugetlbfs_i_mmap_rwsem_key (aka
mapping->i_mmap_rwsem for hugetlb mapping) vs.  i_mmap_rwsem.

huge_pmd_share() does memory allocation under hugetlbfs_i_mmap_rwsem_key
and allocator can take i_mmap_rwsem if it hit reclaim.  So we need to
take i_mmap_rwsem from all hugetlb VMAs before taking i_mmap_rwsem from
rest of VMAs.

The patch also documents locking order for hugetlbfs_i_mmap_rwsem_key.

[1] http://lkml.kernel.org/r/CACT4Y+Zu95tBs-0EvdiAKzUOsb4tczRRfCRTpLr4bg_OP9HuVg@mail.gmail.com

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Reviewed-by: Michal Hocko <mhocko@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 16 insertions, 15 deletions

diff --git a/mm/rmap.c b/mm/rmap.c
index 68af2e3..79f3bf0 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -23,21 +23,22 @@
  * inode->i_mutex	(while writing or truncating, not reading or faulting)
  *   mm->mmap_sem
  *     page->flags PG_locked (lock_page)
- *       mapping->i_mmap_rwsem
- *         anon_vma->rwsem
- *           mm->page_table_lock or pte_lock
- *             zone->lru_lock (in mark_page_accessed, isolate_lru_page)
- *             swap_lock (in swap_duplicate, swap_info_get)
- *               mmlist_lock (in mmput, drain_mmlist and others)
- *               mapping->private_lock (in __set_page_dirty_buffers)
- *                 mem_cgroup_{begin,end}_page_stat (memcg->move_lock)
- *                   mapping->tree_lock (widely used)
- *               inode->i_lock (in set_page_dirty's __mark_inode_dirty)
- *               bdi.wb->list_lock (in set_page_dirty's __mark_inode_dirty)
- *                 sb_lock (within inode_lock in fs/fs-writeback.c)
- *                 mapping->tree_lock (widely used, in set_page_dirty,
- *                           in arch-dependent flush_dcache_mmap_lock,
- *                           within bdi.wb->list_lock in __sync_single_inode)
+ *       hugetlbfs_i_mmap_rwsem_key (in huge_pmd_share)
+ *         mapping->i_mmap_rwsem
+ *           anon_vma->rwsem
+ *             mm->page_table_lock or pte_lock
+ *               zone->lru_lock (in mark_page_accessed, isolate_lru_page)
+ *               swap_lock (in swap_duplicate, swap_info_get)
+ *                 mmlist_lock (in mmput, drain_mmlist and others)
+ *                 mapping->private_lock (in __set_page_dirty_buffers)
+ *                   mem_cgroup_{begin,end}_page_stat (memcg->move_lock)
+ *                     mapping->tree_lock (widely used)
+ *                 inode->i_lock (in set_page_dirty's __mark_inode_dirty)
+ *                 bdi.wb->list_lock (in set_page_dirty's __mark_inode_dirty)
+ *                   sb_lock (within inode_lock in fs/fs-writeback.c)
+ *                   mapping->tree_lock (widely used, in set_page_dirty,
+ *                             in arch-dependent flush_dcache_mmap_lock,
+ *                             within bdi.wb->list_lock in __sync_single_inode)
  *
  * anon_vma->rwsem,mapping->i_mutex      (memory_failure, collect_procs_anon)
  *   ->tasklist_lock