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mm, debug_pagelloc: use static keys to enable debugging 

Patch series "debug_pagealloc improvements".

I have been recently debugging some pcplist corruptions, where it would be
useful to perform struct page checks immediately as pages are allocated
from and freed to pcplists, which is now only possible by rebuilding the
kernel with CONFIG_DEBUG_VM (details in Patch 2 changelog).

To make this kind of debugging simpler in future on a distro kernel, I
have improved CONFIG_DEBUG_PAGEALLOC so that it has even smaller overhead
when not enabled at boot time (Patch 1) and also when enabled (Patch 3),
and extended it to perform the struct page checks more often when enabled
(Patch 2).  Now it can be configured in when building a distro kernel
without extra overhead, and debugging page use after free or double free
can be enabled simply by rebooting with debug_pagealloc=on.

This patch (of 3):

CONFIG_DEBUG_PAGEALLOC has been redesigned by 031bc5743f
("mm/debug-pagealloc: make debug-pagealloc boottime configurable") to
allow being always enabled in a distro kernel, but only perform its
expensive functionality when booted with debug_pagelloc=on.  We can
further reduce the overhead when not boot-enabled (including page
allocator fast paths) using static keys.  This patch introduces one for
debug_pagealloc core functionality, and another for the optional guard
page functionality (enabled by booting with debug_guardpage_minorder=X).

Link: http://lkml.kernel.org/r/20190603143451.27353-2-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Andrew Morton <akpm@linux-foundation.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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Vlastimil Babka 2019-07-11 20:55:06 -07:00 committed by Linus Torvalds
parent a9659476d4
commit 96a2b03f28
2 changed files with 28 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

15
include/linux/mm.h
View File

@ -2701,11 +2701,18 @@ static inline void kernel_poison_pages(struct page *page, int numpages,
int enable) { }
#endif
extern bool _debug_pagealloc_enabled;
#ifdef CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT
DECLARE_STATIC_KEY_TRUE(_debug_pagealloc_enabled);
#else
DECLARE_STATIC_KEY_FALSE(_debug_pagealloc_enabled);
#endif
static inline bool debug_pagealloc_enabled(void)
{
return IS_ENABLED(CONFIG_DEBUG_PAGEALLOC) && _debug_pagealloc_enabled;
if (!IS_ENABLED(CONFIG_DEBUG_PAGEALLOC))
return false;
return static_branch_unlikely(&_debug_pagealloc_enabled);
}
#if defined(CONFIG_DEBUG_PAGEALLOC) || defined(CONFIG_ARCH_HAS_SET_DIRECT_MAP)
@ -2859,7 +2866,7 @@ extern struct page_ext_operations debug_guardpage_ops;
#ifdef CONFIG_DEBUG_PAGEALLOC
extern unsigned int _debug_guardpage_minorder;
extern bool _debug_guardpage_enabled;
DECLARE_STATIC_KEY_FALSE(_debug_guardpage_enabled);
static inline unsigned int debug_guardpage_minorder(void)
{
@ -2868,7 +2875,7 @@ static inline unsigned int debug_guardpage_minorder(void)
static inline bool debug_guardpage_enabled(void)
{
return _debug_guardpage_enabled;
return static_branch_unlikely(&_debug_guardpage_enabled);
}
static inline bool page_is_guard(struct page *page)

23
mm/page_alloc.c
View File

@ -644,16 +644,27 @@ void prep_compound_page(struct page *page, unsigned int order)
#ifdef CONFIG_DEBUG_PAGEALLOC
unsigned int _debug_guardpage_minorder;
bool _debug_pagealloc_enabled __read_mostly
= IS_ENABLED(CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT);
#ifdef CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT
DEFINE_STATIC_KEY_TRUE(_debug_pagealloc_enabled);
#else
DEFINE_STATIC_KEY_FALSE(_debug_pagealloc_enabled);
#endif
EXPORT_SYMBOL(_debug_pagealloc_enabled);
bool _debug_guardpage_enabled __read_mostly;
DEFINE_STATIC_KEY_FALSE(_debug_guardpage_enabled);
static int __init early_debug_pagealloc(char *buf)
{
if (!buf)
bool enable = false;
if (kstrtobool(buf, &enable))
return -EINVAL;
return kstrtobool(buf, &_debug_pagealloc_enabled);
if (enable)
static_branch_enable(&_debug_pagealloc_enabled);
return 0;
}
early_param("debug_pagealloc", early_debug_pagealloc);
@ -677,7 +688,7 @@ static void init_debug_guardpage(void)
if (!debug_guardpage_minorder())
return;
_debug_guardpage_enabled = true;
static_branch_enable(&_debug_guardpage_enabled);
}
struct page_ext_operations debug_guardpage_ops = {