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);
On Dec 19, 2019, at 8:06 AM, Vlastimil Babka vbabka@suse.cz wrote:
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.
This was daily tested on linux-next here for those arches and never saw an issue. Are you able to reproduce it on mainline or linux-next?
On 12/19/19 2:16 PM, Qian Cai wrote:
On Dec 19, 2019, at 8:06 AM, Vlastimil Babka vbabka@suse.cz wrote:
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.
This was daily tested on linux-next here for those arches and never saw an issue.
Well I assume nobody has booted the kernel specifically with debug_pagealloc=on. In case a randconfig run enabled CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT then the problem wouldn't manifest as the static key would be initialized with DEFINE_STATIC_KEY_TRUE by the compiler itself, and the enabling-by-param would be a no-op.
Are you able to reproduce it on mainline or linux-next?
I didn't try, but our kernel is 5.3-based so that's quite recent. The offending commit was also introduced in 5.3-rc1 so there's that.
On Thu, 19 Dec 2019 14:06:12 +0100 Vlastimil Babka vbabka@suse.cz wrote:
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.
I'm seeing this with x86_64 allmodconfig:
ERROR: "_debug_pagealloc_enabled_early" [sound/drivers/pcsp/snd-pcsp.ko] undefined!
Not sure why. It's there:
q:/usr/src/25> nm mm/page_alloc.o|grep _debug_pagealloc_enabled ... 00000000000028a0 B _debug_pagealloc_enabled ...
and exported:
0000000000000072 r __kstrtab__debug_pagealloc_enabled
Odd. Does this happen to you as well?
On 1/3/20 4:02 AM, Andrew Morton wrote:
On Thu, 19 Dec 2019 14:06:12 +0100 Vlastimil Babka vbabka@suse.cz wrote:
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.
I'm seeing this with x86_64 allmodconfig:
ERROR: "_debug_pagealloc_enabled_early" [sound/drivers/pcsp/snd-pcsp.ko] undefined!
Not sure why. It's there:
q:/usr/src/25> nm mm/page_alloc.o|grep _debug_pagealloc_enabled ... 00000000000028a0 B _debug_pagealloc_enabled ...
and exported:
0000000000000072 r __kstrtab__debug_pagealloc_enabled
Hm that's not the _early version. Missing export indeed, can you amend with Stephen's patch? Thanks!
https://lore.kernel.org/linux-next/20200106164944.063ac07b@canb.auug.org.au/
Odd. Does this happen to you as well?
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