[PATCH v2] mm: slub: call WARN() instead of pr_err on slab_fix.

[Hyesoo Yu <hyesoo.yu@xxxxxxxxxxx>]

If a slab object is corrupted or an error occurs in its internal
value, continuing after restoration may cause other side effects.
At this point, it is difficult to debug because the problem occurred
in the past. It is better to use WARN() instead of pr_err to catch
errors at the point of issue because WARN() could trigger panic for
system debugging when panic_on_warn is enabled. WARN() should be
called prior to fixing the value because when a panic is triggered by WARN(),
it allows us to check corrupted data.

Changes in v2:
- Replace direct calling with BUG_ON with the use of WARN in slab_fix.

Signed-off-by: Hyesoo Yu <hyesoo.yu@xxxxxxxxxxx>
---
 mm/slub.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 1f50129dcfb3..ea956cb4b8be 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1043,7 +1043,7 @@ static void slab_fix(struct kmem_cache *s, char *fmt, ...)
 	va_start(args, fmt);
 	vaf.fmt = fmt;
 	vaf.va = &args;
-	pr_err("FIX %s: %pV\n", s->name, &vaf);
+	WARN(1, "FIX %s: %pV\n", s->name, &vaf);
 	va_end(args);
 }
 
@@ -1106,8 +1106,8 @@ static bool freelist_corrupted(struct kmem_cache *s, struct slab *slab,
 	if ((s->flags & SLAB_CONSISTENCY_CHECKS) &&
 	    !check_valid_pointer(s, slab, nextfree) && freelist) {
 		object_err(s, slab, *freelist, "Freechain corrupt");
-		*freelist = NULL;
 		slab_fix(s, "Isolate corrupted freechain");
+		*freelist = NULL;
 		return true;
 	}
 
@@ -1445,9 +1445,9 @@ static int on_freelist(struct kmem_cache *s, struct slab *slab, void *search)
 				set_freepointer(s, object, NULL);
 			} else {
 				slab_err(s, slab, "Freepointer corrupt");
+				slab_fix(s, "Freelist cleared");
 				slab->freelist = NULL;
 				slab->inuse = slab->objects;
-				slab_fix(s, "Freelist cleared");
 				return 0;
 			}
 			break;
@@ -1464,14 +1464,14 @@ static int on_freelist(struct kmem_cache *s, struct slab *slab, void *search)
 	if (slab->objects != max_objects) {
 		slab_err(s, slab, "Wrong number of objects. Found %d but should be %d",
 			 slab->objects, max_objects);
-		slab->objects = max_objects;
 		slab_fix(s, "Number of objects adjusted");
+		slab->objects = max_objects;
 	}
 	if (slab->inuse != slab->objects - nr) {
 		slab_err(s, slab, "Wrong object count. Counter is %d but counted were %d",
 			 slab->inuse, slab->objects - nr);
-		slab->inuse = slab->objects - nr;
 		slab_fix(s, "Object count adjusted");
+		slab->inuse = slab->objects - nr;
 	}
 	return search == NULL;
 }
-- 
2.48.0