memcg: fix mem_cgroup_print_bad_page

If DEBUG_VM, mem_cgroup_print_bad_page() is called whenever bad_page()
shows a "Bad page state" message, removes page from circulation, adds a
taint and continues.  This is at a very low level, often when a spinlock
is held (sometimes when page table lock is held, for example).

We want to recover from this badness, not make it worse: we must not
kmalloc memory here, we must not do a cgroup path lookup via dubious
pointers.  No doubt that code was useful to debug a particular case at one
time, and may be again, but take it out of the mainline kernel.

Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9f2f646..602207b 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3364,23 +3364,8 @@ void mem_cgroup_print_bad_page(struct page *page)
 
        pc = lookup_page_cgroup_used(page);
        if (pc) {
-               int ret = -1;
-               char *path;
-
-               printk(KERN_ALERT "pc:%p pc->flags:%lx pc->mem_cgroup:%p",
+               printk(KERN_ALERT "pc:%p pc->flags:%lx pc->mem_cgroup:%p\n",
                       pc, pc->flags, pc->mem_cgroup);
-
-               path = kmalloc(PATH_MAX, GFP_KERNEL);
-               if (path) {
-                       rcu_read_lock();
-                       ret = cgroup_path(pc->mem_cgroup->css.cgroup,
-                                                       path, PATH_MAX);
-                       rcu_read_unlock();
-               }
-
-               printk(KERN_CONT "(%s)\n",
-                               (ret < 0) ? "cannot get the path" : path);
-               kfree(path);
        }
 }
 #endif