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mm, slab: Check GFP_SLAB_BUG_MASK before alloc_pages in kmalloc_order

PATCH Superseded Long Li 2 participants 2 messages Jun 30, 2020

Subsystems (2)
Memory management Slab allocator

v2 of 6 Superseded Latest is v6 →

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Long Li

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#0 lore raw

PATCH v2 1/1 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 <[email protected]>

---

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(+)
mm/slab_common.c +10 -0
index a143a8c8f874..3548f4f8374b 100644
@@ -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)) {
Signature · 1 line
2.17.1
#1 lore raw
Quoted 40 lines · 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 <[email protected]>

---

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(+)
mm/slab_common.c +1 -0
index a143a8c8f874..3548f4f8374b 100644
@@ -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;

mm/slab_common.c void *kmalloc_order(size_t size, gfp_t flags, unsigned int order) · line 828

Quoted 10 lines
mm/slab_common.c +9 -0
+	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;

Oh, this is really good! I hadn't actually looked at how slab/slub handle GFP_SLAB_BUG_MASK. If you don't mind though, I would suggest that this code should all be in one place. Perhaps:

gfp_t kmalloc_invalid_flags(gfp_t flags)

{
	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();

	return flags;
}

and then call it from the three places?

Also, the changelog could do with a bit of work. Perhaps:

kmalloc cannot allocate memory from HIGHMEM. Allocating large amounts of memory currently bypasses the check and will simply leak the memory when page_address() returns NULL. To fix this, factor the GFP_SLAB_BUG_MASK check out of slab & slub, and call it from kmalloc_order() as well.