From: Vlastimil Babka <vbabka@xxxxxxx>
Subject: mm, debug_pagealloc: don't rely on static keys too early
Commit 96a2b03f281d ("mm, debug_pagelloc: use static keys to enable
debugging") has introduced a static key to reduce overhead when
debug_pagealloc is compiled in but not enabled. It relied on the
assumption that jump_label_init() is called before parse_early_param() as
in start_kernel(), so when the "debug_pagealloc=on" option is parsed, it
is safe to enable the static key.
However, it turns out multiple architectures call parse_early_param()
earlier from their setup_arch(). x86 also calls jump_label_init() even
earlier, so no issue was found while testing the commit, but same is not
true for e.g. ppc64 and s390 where the kernel would not boot with
debug_pagealloc=on as found by our QA.
To fix this without tricky changes to init code of multiple architectures,
this patch partially reverts the static key conversion from 96a2b03f281d.
Init-time and non-fastpath calls (such as in arch code) of
debug_pagealloc_enabled() will again test a simple bool variable.
Fastpath mm code is converted to a new debug_pagealloc_enabled_static()
variant that relies on the static key, which is enabled in a well-defined
point in mm_init() where it's guaranteed that jump_label_init() has been
called, regardless of architecture.
[sfr@xxxxxxxxxxxxxxxx: export _debug_pagealloc_enabled_early]
Link: http://lkml.kernel.org/r/20200106164944.063ac07b@xxxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/20191219130612.23171-1-vbabka@xxxxxxx
Fixes: 96a2b03f281d ("mm, debug_pagelloc: use static keys to enable debugging")
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Qian Cai <cai@xxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/mm.h | 18 +++++++++++++++---
init/main.c | 1 +
mm/page_alloc.c | 37 +++++++++++++------------------------
mm/slab.c | 4 ++--
mm/slub.c | 2 +-
mm/vmalloc.c | 4 ++--
6 files changed, 34 insertions(+), 32 deletions(-)
--- a/include/linux/mm.h~mm-debug_pagealloc-dont-rely-on-static-keys-too-early
+++ a/include/linux/mm.h
@@ -2658,14 +2658,26 @@ static inline bool want_init_on_free(voi
!page_poisoning_enabled();
}
-#ifdef CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT
-DECLARE_STATIC_KEY_TRUE(_debug_pagealloc_enabled);
+#ifdef CONFIG_DEBUG_PAGEALLOC
+extern void init_debug_pagealloc(void);
#else
-DECLARE_STATIC_KEY_FALSE(_debug_pagealloc_enabled);
+static inline void init_debug_pagealloc(void) {}
#endif
+extern bool _debug_pagealloc_enabled_early;
+DECLARE_STATIC_KEY_FALSE(_debug_pagealloc_enabled);
static inline bool debug_pagealloc_enabled(void)
{
+ return IS_ENABLED(CONFIG_DEBUG_PAGEALLOC) &&
+ _debug_pagealloc_enabled_early;
+}
+
+/*
+ * For use in fast paths after init_debug_pagealloc() has run, or when a
+ * false negative result is not harmful when called too early.
+ */
+static inline bool debug_pagealloc_enabled_static(void)
+{
if (!IS_ENABLED(CONFIG_DEBUG_PAGEALLOC))
return false;
--- a/init/main.c~mm-debug_pagealloc-dont-rely-on-static-keys-too-early
+++ a/init/main.c
@@ -553,6 +553,7 @@ static void __init mm_init(void)
* bigger than MAX_ORDER unless SPARSEMEM.
*/
page_ext_init_flatmem();
+ init_debug_pagealloc();
report_meminit();
mem_init();
kmem_cache_init();
--- a/mm/page_alloc.c~mm-debug_pagealloc-dont-rely-on-static-keys-too-early
+++ a/mm/page_alloc.c
@@ -694,34 +694,27 @@ void prep_compound_page(struct page *pag
#ifdef CONFIG_DEBUG_PAGEALLOC
unsigned int _debug_guardpage_minorder;
-#ifdef CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT
-DEFINE_STATIC_KEY_TRUE(_debug_pagealloc_enabled);
-#else
+bool _debug_pagealloc_enabled_early __read_mostly
+ = IS_ENABLED(CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT);
+EXPORT_SYMBOL(_debug_pagealloc_enabled_early);
DEFINE_STATIC_KEY_FALSE(_debug_pagealloc_enabled);
-#endif
EXPORT_SYMBOL(_debug_pagealloc_enabled);
DEFINE_STATIC_KEY_FALSE(_debug_guardpage_enabled);
static int __init early_debug_pagealloc(char *buf)
{
- bool enable = false;
-
- if (kstrtobool(buf, &enable))
- return -EINVAL;
-
- if (enable)
- static_branch_enable(&_debug_pagealloc_enabled);
-
- return 0;
+ return kstrtobool(buf, &_debug_pagealloc_enabled_early);
}
early_param("debug_pagealloc", early_debug_pagealloc);
-static void init_debug_guardpage(void)
+void init_debug_pagealloc(void)
{
if (!debug_pagealloc_enabled())
return;
+ static_branch_enable(&_debug_pagealloc_enabled);
+
if (!debug_guardpage_minorder())
return;
@@ -1186,7 +1179,7 @@ static __always_inline bool free_pages_p
*/
arch_free_page(page, order);
- if (debug_pagealloc_enabled())
+ if (debug_pagealloc_enabled_static())
kernel_map_pages(page, 1 << order, 0);
kasan_free_nondeferred_pages(page, order);
@@ -1207,7 +1200,7 @@ static bool free_pcp_prepare(struct page
static bool bulkfree_pcp_prepare(struct page *page)
{
- if (debug_pagealloc_enabled())
+ if (debug_pagealloc_enabled_static())
return free_pages_check(page);
else
return false;
@@ -1221,7 +1214,7 @@ static bool bulkfree_pcp_prepare(struct
*/
static bool free_pcp_prepare(struct page *page)
{
- if (debug_pagealloc_enabled())
+ if (debug_pagealloc_enabled_static())
return free_pages_prepare(page, 0, true);
else
return free_pages_prepare(page, 0, false);
@@ -1973,10 +1966,6 @@ void __init page_alloc_init_late(void)
for_each_populated_zone(zone)
set_zone_contiguous(zone);
-
-#ifdef CONFIG_DEBUG_PAGEALLOC
- init_debug_guardpage();
-#endif
}
#ifdef CONFIG_CMA
@@ -2106,7 +2095,7 @@ static inline bool free_pages_prezeroed(
*/
static inline bool check_pcp_refill(struct page *page)
{
- if (debug_pagealloc_enabled())
+ if (debug_pagealloc_enabled_static())
return check_new_page(page);
else
return false;
@@ -2128,7 +2117,7 @@ static inline bool check_pcp_refill(stru
}
static inline bool check_new_pcp(struct page *page)
{
- if (debug_pagealloc_enabled())
+ if (debug_pagealloc_enabled_static())
return check_new_page(page);
else
return false;
@@ -2155,7 +2144,7 @@ inline void post_alloc_hook(struct page
set_page_refcounted(page);
arch_alloc_page(page, order);
- if (debug_pagealloc_enabled())
+ if (debug_pagealloc_enabled_static())
kernel_map_pages(page, 1 << order, 1);
kasan_alloc_pages(page, order);
kernel_poison_pages(page, 1 << order, 1);
--- a/mm/slab.c~mm-debug_pagealloc-dont-rely-on-static-keys-too-early
+++ a/mm/slab.c
@@ -1416,7 +1416,7 @@ static void kmem_rcu_free(struct rcu_hea
#if DEBUG
static bool is_debug_pagealloc_cache(struct kmem_cache *cachep)
{
- if (debug_pagealloc_enabled() && OFF_SLAB(cachep) &&
+ if (debug_pagealloc_enabled_static() && OFF_SLAB(cachep) &&
(cachep->size % PAGE_SIZE) == 0)
return true;
@@ -2008,7 +2008,7 @@ int __kmem_cache_create(struct kmem_cach
* to check size >= 256. It guarantees that all necessary small
* sized slab is initialized in current slab initialization sequence.
*/
- if (debug_pagealloc_enabled() && (flags & SLAB_POISON) &&
+ if (debug_pagealloc_enabled_static() && (flags & SLAB_POISON) &&
size >= 256 && cachep->object_size > cache_line_size()) {
if (size < PAGE_SIZE || size % PAGE_SIZE == 0) {
size_t tmp_size = ALIGN(size, PAGE_SIZE);
--- a/mm/slub.c~mm-debug_pagealloc-dont-rely-on-static-keys-too-early
+++ a/mm/slub.c
@@ -288,7 +288,7 @@ static inline void *get_freepointer_safe
unsigned long freepointer_addr;
void *p;
- if (!debug_pagealloc_enabled())
+ if (!debug_pagealloc_enabled_static())
return get_freepointer(s, object);
freepointer_addr = (unsigned long)object + s->offset;
--- a/mm/vmalloc.c~mm-debug_pagealloc-dont-rely-on-static-keys-too-early
+++ a/mm/vmalloc.c
@@ -1383,7 +1383,7 @@ static void free_unmap_vmap_area(struct
{
flush_cache_vunmap(va->va_start, va->va_end);
unmap_vmap_area(va);
- if (debug_pagealloc_enabled())
+ if (debug_pagealloc_enabled_static())
flush_tlb_kernel_range(va->va_start, va->va_end);
free_vmap_area_noflush(va);
@@ -1681,7 +1681,7 @@ static void vb_free(const void *addr, un
vunmap_page_range((unsigned long)addr, (unsigned long)addr + size);
- if (debug_pagealloc_enabled())
+ if (debug_pagealloc_enabled_static())
flush_tlb_kernel_range((unsigned long)addr,
(unsigned long)addr + size);
_
