mm/debug.c: fix __dump_page when mapping->host is not set
authorOscar Salvador <osalvador@suse.de>
Fri, 29 Mar 2019 03:44:01 +0000 (20:44 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Fri, 29 Mar 2019 17:01:37 +0000 (10:01 -0700)
commit5ae2efb1dea9f537453e841714e3ee2757595aec
treeec6d21ee6dcb327485349c6605b57992caffd00e
parenta7f40cfe3b7ada57af9b62fd28430eeb4a7cfcb7
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@suse.de
Fixes: 1c6fb1d89e73c ("mm: print more information about mapping in __dump_page")
Signed-off-by: Oscar Salvador <osalvador@suse.de>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/debug.c