linux-kernel - [PATCH 3/6] slab: move validate_slab_ptr() from check

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Message-Id: <20250911-slub-slab-validation-v1-3-8b67eb3b3dc5@suse.cz>
Date: Thu, 11 Sep 2025 19:02:36 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc: Harry Yoo <harry.yoo@...cle.com>, Christoph Lameter <cl@...two.org>, 
 David Rientjes <rientjes@...gle.com>, 
 Roman Gushchin <roman.gushchin@...ux.dev>, 
 Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org, 
 linux-kernel@...r.kernel.org, Vlastimil Babka <vbabka@...e.cz>
Subject: [PATCH 3/6] slab: move validate_slab_ptr() from check_slab() to
 its callers

We will want to do the validation earlier in some callers or remove it
completely, so extract it from check_slab() first. No functional change.

Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
---
 mm/slub.c | 25 ++++++++++++++++++++-----
 1 file changed, 20 insertions(+), 5 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 5bbfe4ee8d9846ec9a34584c10750388849da3b9..94a089205a86f0667444484e158d307e72cd96e1 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1458,15 +1458,15 @@ static int check_object(struct kmem_cache *s, struct slab *slab,
 	return ret;
 }
 
+/*
+ * Checks if the slab state looks sane. Assumes the struct slab pointer
+ * was either obtained in a way that ensures it's valid, or validated
+ * by validate_slab_ptr()
+ */
 static int check_slab(struct kmem_cache *s, struct slab *slab)
 {
 	int maxobj;
 
-	if (!validate_slab_ptr(slab)) {
-		slab_err(s, slab, "Not a valid slab page");
-		return 0;
-	}
-
 	maxobj = order_objects(slab_order(slab), s->size);
 	if (slab->objects > maxobj) {
 		slab_err(s, slab, "objects %u > max %u",
@@ -1633,6 +1633,11 @@ void setup_slab_debug(struct kmem_cache *s, struct slab *slab, void *addr)
 static inline int alloc_consistency_checks(struct kmem_cache *s,
 					struct slab *slab, void *object)
 {
+	if (!validate_slab_ptr(slab)) {
+		slab_err(s, slab, "Not a valid slab page");
+		return 0;
+	}
+
 	if (!check_slab(s, slab))
 		return 0;
 
@@ -3485,6 +3490,11 @@ static inline bool free_debug_processing(struct kmem_cache *s,
 	int cnt = 0;
 
 	if (s->flags & SLAB_CONSISTENCY_CHECKS) {
+		if (!validate_slab_ptr(slab)) {
+			slab_err(s, slab, "Not a valid slab page");
+			goto out;
+		}
+
 		if (!check_slab(s, slab))
 			goto out;
 	}
@@ -6519,6 +6529,11 @@ static void validate_slab(struct kmem_cache *s, struct slab *slab,
 	void *p;
 	void *addr = slab_address(slab);
 
+	if (!validate_slab_ptr(slab)) {
+		slab_err(s, slab, "Not a valid slab page");
+		return;
+	}
+
 	if (!check_slab(s, slab) || !on_freelist(s, slab, NULL))
 		return;
 

-- 
2.51.0