[PATCH v2] mm, slab: Check GFP_SLAB_BUG_MASK before alloc_pages in kmalloc_order

[Long Li]

In the ARM32 environment with highmem enabled. Using flag of kmalloc()
with __GFP_HIGHMEM to allocate large memory, it will go through the
kmalloc_order() path and return NULL. The __GFP_HIGHMEM flag will
cause alloc_pages() to allocate highmem memory and pages cannot be
directly converted to a virtual address, kmalloc_order() will return
NULL and the page has been allocated.

After modification, GFP_SLAB_BUG_MASK has been checked before
allocating pages, refer to the new_slab().

Signed-off-by: Long Li <lonuxli.64@xxxxxxxxx>
---

Changes in v2:
- patch is rebased againest "[PATCH] mm: Free unused pages in
kmalloc_order()" [1]
- check GFP_SLAB_BUG_MASK and generate warnings before alloc_pages
in kmalloc_order()

[1] https://lkml.org/lkml/2020/6/27/16

 mm/slab_common.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index a143a8c8f874..3548f4f8374b 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -27,6 +27,7 @@
 #include <trace/events/kmem.h>
 
 #include "slab.h"
+#include "internal.h"
 
 enum slab_state slab_state;
 LIST_HEAD(slab_caches);
@@ -815,6 +816,15 @@ void *kmalloc_order(size_t size, gfp_t flags, unsigned int order)
 	void *ret = NULL;
 	struct page *page;
 
+	if (unlikely(flags & GFP_SLAB_BUG_MASK)) {
+		gfp_t invalid_mask = flags & GFP_SLAB_BUG_MASK;
+
+		flags &= ~GFP_SLAB_BUG_MASK;
+		pr_warn("Unexpected gfp: %#x (%pGg). Fixing up to gfp: %#x (%pGg). Fix your code!\n",
+				invalid_mask, &invalid_mask, flags, &flags);
+		dump_stack();
+	}
+
 	flags |= __GFP_COMP;
 	page = alloc_pages(flags, order);
 	if (likely(page)) {
-- 
2.17.1