mm: document tree_lock->zone.lock lockorder

zone->lock is quite an "inner" lock and mostly constrained to page alloc as
well, so like slab locks, it probably isn't something that is critically
important to document here.  However unlike slab locks, zone lock could be
used more widely in future, and page_alloc.c might possibly have more
business to do tricky things with pagecache than does slab.  So...  I don't
think it hurts to document it.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/filemap.c b/mm/filemap.c
index c6049e947cd9968a2870ed0805f5aae5ed4355ff..4fb1546bbad6abd95dd33f5281c88517540631fb 100644 (file)
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -63,6 +63,7 @@ generic_file_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
  *    ->private_lock           (__free_pte->__set_page_dirty_buffers)
  *      ->swap_lock            (exclusive_swap_page, others)
  *        ->mapping->tree_lock
+ *          ->zone.lock
  *
  *  ->i_mutex
  *    ->i_mmap_lock            (truncate->unmap_mapping_range)

diff --git a/mm/rmap.c b/mm/rmap.c
index f6e85d7a7e459c0173d401336c0b14bd43c411c4..8990f909492f31d8a3f01df258907661db1bccf6 100644 (file)
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -36,6 +36,7 @@
  *                 mapping->tree_lock (widely used, in set_page_dirty,
  *                           in arch-dependent flush_dcache_mmap_lock,
  *                           within inode_lock in __sync_single_inode)
+ *                   zone->lock (within radix tree node alloc)
  */
 
 #include <linux/mm.h>