[PATCH] mm/slub: free returned pfmemalloc sheaves via free_empty_sheaf()

[hu.shengming]

From: Shengming Hu <hu.shengming@xxxxxxxxxx>

Regular sized sheaves are allocated through alloc_empty_sheaf(), which
sets __GFP_NO_OBJ_EXT. free_empty_sheaf() is the matching free helper
for such sheaves. It marks kmalloc sheaves with an empty codetag before
kfree(), avoiding the alloc_tag_sub() warning for intentionally missing
object extensions.

kmem_cache_return_sheaf() currently handles returned pfmemalloc sheaves
in the same branch as oversize sheaves and uses kfree(). That is right
for oversize sheaves, which are allocated directly with kzalloc_flex(),
but it misses the matching free path for regular sized pfmemalloc sheaves
that came from alloc_empty_sheaf().

Split the two cases. Keep plain kfree() for capacity-mismatched oversize
sheaves, and use free_empty_sheaf() after flushing returned pfmemalloc
regular sheaves.

Fixes: <1ce20c2> ("slab: handle pfmemalloc slabs properly with sheaves")
Signed-off-by: Shengming Hu <hu.shengming@xxxxxxxxxx>
---
 mm/slub.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 04692a6f9128..a6b720fa79ad 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -5094,13 +5094,18 @@ void kmem_cache_return_sheaf(struct kmem_cache *s, gfp_t gfp,
 	struct slub_percpu_sheaves *pcs;
 	struct node_barn *barn;

-	if (unlikely((sheaf->capacity != s->sheaf_capacity)
-		     || sheaf->pfmemalloc)) {
+	if (unlikely(sheaf->capacity != s->sheaf_capacity)) {
 		sheaf_flush_unused(s, sheaf);
 		kfree(sheaf);
 		return;
 	}

+	if (unlikely(sheaf->pfmemalloc)) {
+		sheaf_flush_unused(s, sheaf);
+		free_empty_sheaf(s, sheaf);
+		return;
+	}
+
 	local_lock(&s->cpu_sheaves->lock);
 	pcs = this_cpu_ptr(s->cpu_sheaves);
 	barn = get_barn(s);
-- 
2.25.1