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.
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
---
mm/shmem.c | 5 +----
1 file changed, 1 insertion(+), 4 deletions(-)
--- 4.9-rc8/mm/shmem.c 2016-11-13 11:44:43.052622519 -0800
+++ linux/mm/shmem.c 2016-12-05 18:54:25.348596732 -0800
@@ -2131,10 +2131,7 @@ static struct inode *shmem_get_inode(str
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
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