From 5ae2efb1dea9f537453e841714e3ee2757595aec Mon Sep 17 00:00:00 2001 From: Oscar Salvador Date: Thu, 28 Mar 2019 20:44:01 -0700 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@suse.de Fixes: 1c6fb1d89e73c ("mm: print more information about mapping in __dump_page") Signed-off-by: Oscar Salvador Acked-by: Michal Hocko Acked-by: Hugh Dickins Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/debug.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/debug.c b/mm/debug.c index 45d9eb77b84e..eee9c221280c 100644 --- a/mm/debug.c +++ b/mm/debug.c @@ -79,7 +79,7 @@ void __dump_page(struct page *page, const char *reason) 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); -- cgit v1.2.3-58-ga151