slub: Reflow ___slab_alloc()

JIRA: https://issues.redhat.com/browse/RHEL-125520
CVE: CVE-2025-39843

This patch is a backport of the following upstream commit:
commit 24c6a09
Author: Chengming Zhou <zhouchengming@bytedance.com>
Date:   Thu Nov 2 03:23:22 2023 +0000

    slub: Reflow ___slab_alloc()

    The get_partial() interface used in ___slab_alloc() may return a single
    object in the "kmem_cache_debug(s)" case, in which we will just return
    the "freelist" object.

    Move this handling up to prepare for later changes.

    And the "pfmemalloc_match()" part is not needed for node partial slab,
    since we already check this in the get_partial_node().

    Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
    Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
    Tested-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
    Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
    Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

Signed-off-by: Audra Mitchell <audra@redhat.com>

Author: Audra Mitchell

mm/slub.c

@@ -3514,8 +3514,21 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 	pc.slab = &slab;
 	pc.orig_size = orig_size;
 	freelist = get_partial(s, node, &pc);
-	if (freelist)
-		goto check_new_slab;
+	if (freelist) {
+		if (kmem_cache_debug(s)) {
+			/*
+			 * For debug caches here we had to go through
+			 * alloc_single_from_partial() so just store the
+			 * tracking info and return the object.
+			 */
+			if (s->flags & SLAB_STORE_USER)
+				set_track(s, freelist, TRACK_ALLOC, addr);
+
+			return freelist;
+		}
+
+		goto retry_load_slab;
+	}
 
 	slub_put_cpu_ptr(s->cpu_slab);
 	slab = new_slab(s, gfpflags, node);
@@ -3551,20 +3564,6 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 
 	inc_slabs_node(s, slab_nid(slab), slab->objects);
 
-check_new_slab:
-
-	if (kmem_cache_debug(s)) {
-		/*
-		 * For debug caches here we had to go through
-		 * alloc_single_from_partial() so just store the tracking info
-		 * and return the object
-		 */
-		if (s->flags & SLAB_STORE_USER)
-			set_track(s, freelist, TRACK_ALLOC, addr);
-
-		return freelist;
-	}
-
 	if (unlikely(!pfmemalloc_match(slab, gfpflags))) {
 		/*
 		 * For !pfmemalloc_match() case we don't load freelist so that