From: Vlastimil Babka vbabka@suse.cz 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@canb.auug.org.au: export _debug_pagealloc_enabled_early] Link: http://lkml.kernel.org/r/20200106164944.063ac07b@canb.auug.org.au Link: http://lkml.kernel.org/r/20191219130612.23171-1-vbabka@suse.cz Fixes: 96a2b03f281d ("mm, debug_pagelloc: use static keys to enable debugging") Signed-off-by: Vlastimil Babka vbabka@suse.cz Signed-off-by: Stephen Rothwell sfr@canb.auug.org.au 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 Cc: Qian Cai cai@lca.pw Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

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);

_