From: Oscar Salvador <osalvador@xxxxxxx>
Subject: mm/debug.c: fix __dump_page when mapping->host is not set
While debugging something, I added a dump_page() into do_swap_page(), and
I got the splat from below. The issue happens when dereferencing
mapping->host in __dump_page():
...
else if (mapping) {
pr_warn("%ps ", mapping->a_ops);
if (mapping->host->i_dentry.first) {
struct dentry *dentry;
dentry = container_of(mapping->host->i_dentry.first, struct dentry, d_u.d_alias);
pr_warn("name:\"%pd\" ", dentry);
}
}
...
Swap address space does not contain an inode information, and so
mapping->host equals NULL.
Although the dump_page() call was added artificially into do_swap_page(),
I am not sure if we can hit this from any other path, so it looks worth
fixing it. We can easily do that by checking mapping->host first.
Link: http://lkml.kernel.org/r/20190318072931.29094-1-osalvador@xxxxxxx
Fixes: 1c6fb1d89e73c ("mm: print more information about mapping in __dump_page")
Signed-off-by: Oscar Salvador <osalvador@xxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Acked-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/debug.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/mm/debug.c~mm-fix-__dump_page-when-mapping-host-is-not-set
+++ a/mm/debug.c
@@ -79,7 +79,7 @@ void __dump_page(struct page *page, cons
pr_warn("ksm ");
else if (mapping) {
pr_warn("%ps ", mapping->a_ops);
- if (mapping->host->i_dentry.first) {
+ if (mapping->host && mapping->host->i_dentry.first) {
struct dentry *dentry;
dentry = container_of(mapping->host->i_dentry.first, struct dentry, d_u.d_alias);
pr_warn("name:\"%pd\" ", dentry);
_
