[patch slab/urgent] disallow changing cpu_partial from userspacefor debug caches

[David Rientjes]

For caches with debugging enabled, "slub: Switch per cpu partial page 
support off for debugging" changes cpu_partial to 0.  It shouldn't be 
tunable from userspace for such caches, otherwise the same accounting 
issues arise during validation.

This patch disallows tuning /sys/kernel/slab/cache/cpu_partial to be non-
zero for caches with debugging enabled.

Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
---
 mm/slub.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -4639,6 +4639,8 @@ static ssize_t cpu_partial_store(struct kmem_cache *s, const char *buf,
 	err = strict_strtoul(buf, 10, &objects);
 	if (err)
 		return err;
+	if (objects && kmem_cache_debug(s))
+		return -EINVAL;
 
 	s->cpu_partial = objects;
 	flush_all(s);
--
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