[PATCH] lib/stackdepot: allow optional init and stack_table allocation by kvmalloc() - fixup

[Vlastimil Babka]

On FLATMEM, we call page_ext_init_flatmem_late() just before kmem_cache_init()
which means stack_depot_init() (called by page owner init) will not recognize
properly it should use kvmalloc() and not memblock_alloc(). memblock_alloc()
will also not issue a warning and return a block memory that can be invalid and
cause kernel page fault when saving stacks, as reported by the kernel test
robot [1].

Fix this by moving page_ext_init_flatmem_late() below kmem_cache_init() so that
slab_is_available() is true during stack_depot_init(). SPARSEMEM doesn't have
this issue, as it doesn't do page_ext_init_flatmem_late(), but a different
page_ext_init() even later in the boot process.

Thanks to Mike Rapoport for pointing out the FLATMEM init ordering issue.

While at it, also actually resolve a checkpatch warning in stack_depot_init()
from DRM CI, which was supposed to be in the original patch already.

[1] https://lore.kernel.org/all/20211014085450.GC18719@xsang-OptiPlex-9020/

Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
---
 init/main.c      | 7 +++++--
 lib/stackdepot.c | 2 +-
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/init/main.c b/init/main.c
index ca2765c8e45c..0ab632f681c5 100644
--- a/init/main.c
+++ b/init/main.c
@@ -845,9 +845,12 @@ static void __init mm_init(void)
 	stack_depot_early_init();
 	mem_init();
 	mem_init_print_info();
-	/* page_owner must be initialized after buddy is ready */
-	page_ext_init_flatmem_late();
 	kmem_cache_init();
+	/*
+	 * page_owner must be initialized after buddy is ready, and also after
+	 * slab is ready so that stack_depot_init() works properly
+	 */
+	page_ext_init_flatmem_late();
 	kmemleak_init();
 	pgtable_init();
 	debug_objects_mem_init();
diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index 049d7d025d78..1f8ea6d0899b 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -172,7 +172,7 @@ __ref int stack_depot_init(void)
 	static DEFINE_MUTEX(stack_depot_init_mutex);
 
 	mutex_lock(&stack_depot_init_mutex);
-	if (!stack_depot_disable && stack_table == NULL) {
+	if (!stack_depot_disable && !stack_table) {
 		size_t size = (STACK_HASH_SIZE * sizeof(struct stack_record *));
 		int i;
 
-- 
2.33.0