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Subject[PATCH v2] mm, slab: Check GFP_SLAB_BUG_MASK before alloc_pages in kmalloc_order
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@gmail.com>
---

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
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