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Subject[PATCH] mm, debug_pagealloc: don't rely on static keys too early
Date
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.

Fixes: 96a2b03f281d ("mm, debug_pagelloc: use static keys to enable debugging")
Cc: <stable@vger.kernel.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
---
include/linux/mm.h | 18 +++++++++++++++---
init/main.c | 1 +
mm/page_alloc.c | 36 ++++++++++++------------------------
mm/slab.c | 4 ++--
mm/slub.c | 2 +-
mm/vmalloc.c | 4 ++--
6 files changed, 33 insertions(+), 32 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index c97ea3b694e6..5cf260d5e248 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2655,13 +2655,25 @@ static inline bool want_init_on_free(void)
!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;
diff --git a/init/main.c b/init/main.c
index ec3a1463ac69..c93b9cc201fa 100644
--- a/init/main.c
+++ b/init/main.c
@@ -554,6 +554,7 @@ 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();
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 4785a8a2040e..5e3fe156ffb4 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -694,34 +694,26 @@ void prep_compound_page(struct page *page, unsigned int order)
#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);
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 +1178,7 @@ static __always_inline bool free_pages_prepare(struct page *page,
*/
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 +1199,7 @@ static bool free_pcp_prepare(struct page *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 +1213,7 @@ static bool bulkfree_pcp_prepare(struct page *page)
*/
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 +1965,6 @@ 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 +2094,7 @@ static inline bool free_pages_prezeroed(void)
*/
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 +2116,7 @@ static inline bool check_pcp_refill(struct page *page)
}
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 +2143,7 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
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);
diff --git a/mm/slab.c b/mm/slab.c
index f1e1840af533..a89633603b2d 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1416,7 +1416,7 @@ static void kmem_rcu_free(struct rcu_head *head)
#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_cache *cachep, slab_flags_t flags)
* 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);
diff --git a/mm/slub.c b/mm/slub.c
index d11389710b12..8eafccf75940 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -288,7 +288,7 @@ static inline void *get_freepointer_safe(struct kmem_cache *s, void *object)
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;
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 4d3b3d60d893..544cc9a725cf 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1375,7 +1375,7 @@ static void free_unmap_vmap_area(struct vmap_area *va)
{
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);
@@ -1673,7 +1673,7 @@ static void vb_free(const void *addr, unsigned long size)

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);

--
2.24.0
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