linux-kernel - [PATCH v2 2/6] slab: wrap debug slab validation in validate_slab

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Message-Id: <20250915-slub-slab-validation-v2-2-314690fc1532@suse.cz>
Date: Mon, 15 Sep 2025 15:55:09 +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 v2 2/6] slab: wrap debug slab validation in
 validate_slab_ptr()

This will make it clear where we currently cast struct slab to folio
only to check the slab type, and allow to change the implementation
later with memdesc conversion.

For now use a struct page based implementation instead of struct folio
to be compatible with further upcoming changes.

Reviewed-by: Harry Yoo <harry.yoo@...cle.com>
Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
---
 mm/slub.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 56143bfd1ae319d384981c810a5ed84af00f4afa..75e4388d507d1abcbce8c7d5d2581381de46cf4d 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -821,6 +821,15 @@ static inline unsigned int get_orig_size(struct kmem_cache *s, void *object)
 	return *(unsigned int *)p;
 }
 
+/*
+ * For debugging context when we want to check if the struct slab pointer
+ * appears to be valid.
+ */
+static inline bool validate_slab_ptr(struct slab *slab)
+{
+	return PageSlab(slab_page(slab));
+}
+
 #ifdef CONFIG_SLUB_DEBUG
 static unsigned long object_map[BITS_TO_LONGS(MAX_OBJS_PER_PAGE)];
 static DEFINE_SPINLOCK(object_map_lock);
@@ -1453,7 +1462,7 @@ static int check_slab(struct kmem_cache *s, struct slab *slab)
 {
 	int maxobj;
 
-	if (!folio_test_slab(slab_folio(slab))) {
+	if (!validate_slab_ptr(slab)) {
 		slab_err(s, slab, "Not a valid slab page");
 		return 0;
 	}
@@ -1653,7 +1662,7 @@ static noinline bool alloc_debug_processing(struct kmem_cache *s,
 	return true;
 
 bad:
-	if (folio_test_slab(slab_folio(slab))) {
+	if (validate_slab_ptr(slab)) {
 		/*
 		 * If this is a slab page then lets do the best we can
 		 * to avoid issues in the future. Marking all objects
@@ -2818,7 +2827,7 @@ static void *alloc_single_from_partial(struct kmem_cache *s,
 	slab->inuse++;
 
 	if (!alloc_debug_processing(s, slab, object, orig_size)) {
-		if (folio_test_slab(slab_folio(slab)))
+		if (validate_slab_ptr(slab))
 			remove_partial(n, slab);
 		return NULL;
 	}

-- 
2.51.0