[PATCH v2] slab: Warn on duplicate cache names when DEBUG_VM=y

[Pedro Falcato]

Duplicate slab cache names can create havoc for userspace tooling that
expects slab cache names to be unique. This is a reasonable expectation.

Sadly, too many duplicate name problems are out there in the wild, so
simply pr_warn instead of pr_err() + failing the sanity check.

Link: https://lore.kernel.org/linux-fsdevel/2d1d053da1cafb3e7940c4f25952da4f0af34e38.1722293276.git.osandov@xxxxxx/
Signed-off-by: Pedro Falcato <pedro.falcato@xxxxxxxxx>
---
v2:
 - Replace the pr_err() + failure with a simple pr_warn

Contrary to Vlastimil's suggestion, we don't seem to require a refcount
== 0 check, because shutdown_cache already synchronously deletes the cache from the list (even reusing
the same list_head for TYPESAFE_BY_RCU).

 mm/slab_common.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 40b582a014b..1abe6a577d5 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -88,6 +88,19 @@ unsigned int kmem_cache_size(struct kmem_cache *s)
 EXPORT_SYMBOL(kmem_cache_size);
 
 #ifdef CONFIG_DEBUG_VM
+
+static bool kmem_cache_is_duplicate_name(const char *name)
+{
+	struct kmem_cache *s;
+
+	list_for_each_entry(s, &slab_caches, list) {
+		if (!strcmp(s->name, name))
+			return true;
+	}
+
+	return false;
+}
+
 static int kmem_cache_sanity_check(const char *name, unsigned int size)
 {
 	if (!name || in_interrupt() || size > KMALLOC_MAX_SIZE) {
@@ -95,6 +108,11 @@ static int kmem_cache_sanity_check(const char *name, unsigned int size)
 		return -EINVAL;
 	}
 
+	if (kmem_cache_is_duplicate_name(name)) {
+		/* Duplicate names will confuse slabtop, et al */
+		pr_warn("%s: name %s already exists as a cache\n", __func__, name);
+	}
+
 	WARN_ON(strchr(name, ' '));	/* It confuses parsers */
 	return 0;
 }
-- 
2.46.0