[PATCH v4 2/2] mm: slub: call WARN() when the slab detect an error

[Hyesoo Yu <hyesoo.yu@samsung.com>]

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 useful to use WARN() to catch errors at the point
of issue because WARN() could trigger panic for system debugging when
panic_on_warn is enabled. WARN() is added where to detect the error
on slab_err and object_err.

It makes sense to only do the WARN() after printing the logs. slab_err
is splited to __slab_err that calls the WARN() and it is called after
printing logs.

Changes in v4:
- Remove WARN() in kmem_cache_destroy to remove redundant warning.

Changes in v3:
- move the WARN from slab_fix to slab_err, object_err and check_obj to
use WARN on all error reporting paths.

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

Signed-off-by: Hyesoo Yu <hyesoo.yu@samsung.com>
---
 mm/slab_common.c |  3 ---
 mm/slub.c        | 31 +++++++++++++++++++------------
 2 files changed, 19 insertions(+), 15 deletions(-)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 477fa471da18..d13f4ffe252b 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -517,9 +517,6 @@ void kmem_cache_destroy(struct kmem_cache *s)
 	kasan_cache_shutdown(s);
 
 	err = __kmem_cache_shutdown(s);
-	if (!slab_in_kunit_test())
-		WARN(err, "%s %s: Slab cache still has objects when called from %pS",
-		     __func__, s->name, (void *)_RET_IP_);
 
 	list_del(&s->list);
 
diff --git a/mm/slub.c b/mm/slub.c
index 8c13cd43c0fd..4961eeccf3ad 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1096,8 +1096,6 @@ static void print_trailer(struct kmem_cache *s, struct slab *slab, u8 *p)
 		/* Beginning of the filler is the free pointer */
 		print_section(KERN_ERR, "Padding  ", p + off,
 			      size_from_object(s) - off);
-
-	dump_stack();
 }
 
 static void object_err(struct kmem_cache *s, struct slab *slab,
@@ -1109,6 +1107,8 @@ static void object_err(struct kmem_cache *s, struct slab *slab,
 	slab_bug(s, "%s", reason);
 	print_trailer(s, slab, object);
 	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
+
+	WARN_ON(1);
 }
 
 static bool freelist_corrupted(struct kmem_cache *s, struct slab *slab,
@@ -1125,6 +1125,14 @@ static bool freelist_corrupted(struct kmem_cache *s, struct slab *slab,
 	return false;
 }
 
+static void __slab_err(struct slab *slab)
+{
+	print_slab_info(slab);
+	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
+
+	WARN_ON(1);
+}
+
 static __printf(3, 4) void slab_err(struct kmem_cache *s, struct slab *slab,
 			const char *fmt, ...)
 {
@@ -1138,9 +1146,7 @@ static __printf(3, 4) void slab_err(struct kmem_cache *s, struct slab *slab,
 	vsnprintf(buf, sizeof(buf), fmt, args);
 	va_end(args);
 	slab_bug(s, "%s", buf);
-	print_slab_info(slab);
-	dump_stack();
-	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
+	__slab_err(slab);
 }
 
 static void init_object(struct kmem_cache *s, void *object, u8 val)
@@ -1313,9 +1319,10 @@ slab_pad_check(struct kmem_cache *s, struct slab *slab)
 	while (end > fault && end[-1] == POISON_INUSE)
 		end--;
 
-	slab_err(s, slab, "Padding overwritten. 0x%p-0x%p @offset=%tu",
-			fault, end - 1, fault - start);
+	slab_bug(s, "Padding overwritten. 0x%p-0x%p @offset=%tu",
+		 fault, end - 1, fault - start);
 	print_section(KERN_ERR, "Padding ", pad, remainder);
+	__slab_err(slab);
 
 	restore_bytes(s, "slab padding", POISON_INUSE, fault, end);
 }
@@ -5428,14 +5435,13 @@ static int calculate_sizes(struct kmem_cache_args *args, struct kmem_cache *s)
 	return !!oo_objects(s->oo);
 }
 
-static void list_slab_objects(struct kmem_cache *s, struct slab *slab,
-			      const char *text)
+static void list_slab_objects(struct kmem_cache *s, struct slab *slab)
 {
 #ifdef CONFIG_SLUB_DEBUG
 	void *addr = slab_address(slab);
 	void *p;
 
-	slab_err(s, slab, text, s->name);
+	slab_bug(s, "Objects remaining on __kmem_cache_shutdown()");
 
 	spin_lock(&object_map_lock);
 	__fill_map(object_map, s, slab);
@@ -5450,6 +5456,8 @@ static void list_slab_objects(struct kmem_cache *s, struct slab *slab,
 		}
 	}
 	spin_unlock(&object_map_lock);
+
+	__slab_err(slab);
 #endif
 }
 
@@ -5470,8 +5478,7 @@ static void free_partial(struct kmem_cache *s, struct kmem_cache_node *n)
 			remove_partial(n, slab);
 			list_add(&slab->slab_list, &discard);
 		} else {
-			list_slab_objects(s, slab,
-			  "Objects remaining in %s on __kmem_cache_shutdown()");
+			list_slab_objects(s, slab);
 		}
 	}
 	spin_unlock_irq(&n->list_lock);
-- 
2.28.0