tmpfs: change shmem_mapping() to test shmem_aops
authorHugh Dickins <hughd@google.com>
Wed, 22 Feb 2017 23:41:42 +0000 (15:41 -0800)
committerLinus Torvalds <torvalds@linux-foundation.org>
Thu, 23 Feb 2017 00:41:27 +0000 (16:41 -0800)
Callers of shmem_mapping() are interested in whether the mapping is swap
backed - except for uprobes, which is interested in whether it should
use shmem_read_mapping_page().  All these callers are better served by a
shmem_mapping() which checks for shmem_aops, than the current version
which goes through several indirections to find where the inode lives -
and has the surprising effect that a private mmap of /dev/zero satisfies
both vma_is_anonymous() and shmem_mapping(), when that device node is on
devtmpfs.  I don't think anything in the tree suffers from that
surprise, but it caught me out, and is better fixed.

Link: http://lkml.kernel.org/r/alpine.LSU.2.11.1612052148530.13021@eggly.anvils
Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/shmem.c

index 3a7587a0314dc73fb4929a824a74f9b8948ea502..7d52cd4b504ddf019c89061003ce7cfdf8a85ccb 100644 (file)
@@ -2175,10 +2175,7 @@ static struct inode *shmem_get_inode(struct super_block *sb, const struct inode
 
 bool shmem_mapping(struct address_space *mapping)
 {
-       if (!mapping->host)
-               return false;
-
-       return mapping->host->i_sb->s_op == &shmem_ops;
+       return mapping->a_ops == &shmem_aops;
 }
 
 #ifdef CONFIG_TMPFS