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Date: Tue, 22 Nov 2011 13:56:08 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Stanislaw Gruszka <sgruszka@...hat.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
Mel Gorman <mgorman@...e.de>,
Andrea Arcangeli <aarcange@...hat.com>,
"Rafael J. Wysocki" <rjw@...k.pl>,
Christoph Lameter <cl@...ux-foundation.org>
Subject: Re: [PATCH v2 1/3] mm: more intensive memory corruption debug
On Fri, 18 Nov 2011 17:25:05 +0100
Stanislaw Gruszka <sgruszka@...hat.com> wrote:
> With CONFIG_DEBUG_PAGEALLOC configured, cpu will generate exception on
> access (read,write) to not allocated page, what allow to catch code
> which corrupt memory. However kernel is trying to maximalise memory
> usage, hence there is usually not much free pages in the system and
> buggy code usually corrupt some crucial data.
>
> This patch change buddy allocator to keep more free/protected pages
> and interlace free/protected and allocated pages to increase probability
> of catch a corruption.
>
> When kernel is compiled with CONFIG_DEBUG_PAGEALLOC,
> debug_guardpage_minorder defines the minimum order used by the page
> allocator to grant a request. The requested size will be returned with
> the remaining pages used as guard pages.
>
I added this:
The default value of debug_guardpage_minorder is zero: no change
from current behaviour.
correct?
>
> ...
>
> +static int __init debug_guardpage_minorder_setup(char *buf)
> +{
> + unsigned long res;
> +
> + if (kstrtoul(buf, 10, &res) < 0 || res > MAX_ORDER / 2) {
> + printk(KERN_ERR "Bad debug_guardpage_minorder value\n");
> + return 0;
> + }
> + _debug_guardpage_minorder = res;
> + printk(KERN_INFO "Setting debug_guardpage_minorder to %lu\n", res);
> + return 0;
> +}
> +__setup("debug_guardpage_minorder=", debug_guardpage_minorder_setup);
> +
> +static inline void set_page_guard_flg(struct page *page)
"flag" not "flg", please ;)
> +{
> + __set_bit(PAGE_DEBUG_FLAG_GUARD, &page->debug_flags);
> +}
> +
> +static inline void clear_page_guard_flg(struct page *page)
> +{
> + __clear_bit(PAGE_DEBUG_FLAG_GUARD, &page->debug_flags);
> +}
Why is it safe to use the non-atomic bitops here.
Please verify that CONFIG_WANT_PAGE_DEBUG_FLAGS is always reliably
enabled when this feature is turned on.
>
> ...
>
Some changes I made - please review.
Documentation/kernel-parameters.txt | 31 +++++++++++++-------------
mm/page_alloc.c | 12 +++++-----
2 files changed, 22 insertions(+), 21 deletions(-)
diff -puN Documentation/kernel-parameters.txt~mm-more-intensive-memory-corruption-debug-fix Documentation/kernel-parameters.txt
--- a/Documentation/kernel-parameters.txt~mm-more-intensive-memory-corruption-debug-fix
+++ a/Documentation/kernel-parameters.txt
@@ -625,21 +625,22 @@ bytes respectively. Such letter suffixes
debug_guardpage_minorder=
[KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
- parameter allows control order of pages that will be
- intentionally kept free (and hence protected) by buddy
- allocator. Bigger value increase probability of
- catching random memory corruption, but reduce amount
- of memory for normal system use. Maximum possible
- value is MAX_ORDER/2. Setting this parameter to 1 or 2,
- should be enough to identify most random memory
- corruption problems caused by bugs in kernel/drivers
- code when CPU write to (or read from) random memory
- location. Note that there exist class of memory
- corruptions problems caused by buggy H/W or F/W or by
- drivers badly programing DMA (basically when memory is
- written at bus level and CPU MMU is bypassed), which
- are not detectable by CONFIG_DEBUG_PAGEALLOC, hence this
- option would not help tracking down these problems too.
+ parameter allows control of the order of pages that will
+ be intentionally kept free (and hence protected) by the
+ buddy allocator. Bigger value increase the probability
+ of catching random memory corruption, but reduce the
+ amount of memory for normal system use. The maximum
+ possible value is MAX_ORDER/2. Setting this parameter
+ to 1 or 2 should be enough to identify most random
+ memory corruption problems caused by bugs in kernel or
+ driver code when a CPU writes to (or reads from) a
+ random memory location. Note that there exists a class
+ of memory corruptions problems caused by buggy H/W or
+ F/W or by drivers badly programing DMA (basically when
+ memory is written at bus level and the CPU MMU is
+ bypassed) which are not detectable by
+ CONFIG_DEBUG_PAGEALLOC, hence this option will not help
+ tracking down these problems.
debugpat [X86] Enable PAT debugging
diff -puN mm/page_alloc.c~mm-more-intensive-memory-corruption-debug-fix mm/page_alloc.c
--- a/mm/page_alloc.c~mm-more-intensive-memory-corruption-debug-fix
+++ a/mm/page_alloc.c
@@ -441,18 +441,18 @@ static int __init debug_guardpage_minord
}
__setup("debug_guardpage_minorder=", debug_guardpage_minorder_setup);
-static inline void set_page_guard_flg(struct page *page)
+static inline void set_page_guard_flag(struct page *page)
{
__set_bit(PAGE_DEBUG_FLAG_GUARD, &page->debug_flags);
}
-static inline void clear_page_guard_flg(struct page *page)
+static inline void clear_page_guard_flag(struct page *page)
{
__clear_bit(PAGE_DEBUG_FLAG_GUARD, &page->debug_flags);
}
#else
-static inline void set_page_guard_flg(struct page *page) { }
-static inline void clear_page_guard_flg(struct page *page) { }
+static inline void set_page_guard_flag(struct page *page) { }
+static inline void clear_page_guard_flag(struct page *page) { }
#endif
static inline void set_page_order(struct page *page, int order)
@@ -578,7 +578,7 @@ static inline void __free_one_page(struc
* merge with it and move up one order.
*/
if (page_is_guard(buddy)) {
- clear_page_guard_flg(buddy);
+ clear_page_guard_flag(buddy);
set_page_private(page, 0);
__mod_zone_page_state(zone, NR_FREE_PAGES, 1 << order);
} else {
@@ -821,7 +821,7 @@ static inline void expand(struct zone *z
* pages will stay not present in virtual address space
*/
INIT_LIST_HEAD(&page[size].lru);
- set_page_guard_flg(&page[size]);
+ set_page_guard_flag(&page[size]);
set_page_private(&page[size], high);
/* Guard pages are not available for any usage */
__mod_zone_page_state(zone, NR_FREE_PAGES, -(1 << high));
_
--
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