[PATCH] generic debug pagealloc (-v4)

Akinobu Mita
2009-03-07T16:29:24Z

On Fri, Mar 06, 2009 at 12:45:51PM -0800, Andrew Morton wrote:
> > +static void poison_page(struct page *page)
> > +{
> > + void *addr;
> > +
> > + if (PageHighMem(page)) {
> > + /*
> > + * Skip poisoning for highmem pages
> > + */
>
> This isn't a good comment - what it tells us is already utterly obvious
> from the code, and the reader is left with no clue as to _why_ the code
> does this.

OK. I made the poison_highpage()/unpoison_highpage() for poisoning
highmem pages. They are not implemented yet and just have a comment
quoted from your earlier email for someone who want to implement it.

> Adding 32 bits to the pageframe for a single feature which needs one
> bit is rather sad. Sure, this is a super-slow feature and nobody will
> be turning it on in production. But I wonder if we can do better.
>
>
> #ifdef CONFIG_WANT_PAGE_DEBUG_FLAGS
> unsigned long debug_flags; /* Use atomic bitops on this */
> #endif
> };
>
> #define PAGE_DEBUG_FLAG_PAGEALLOC 0
> #define PAGE_DEBUG_SOMETHING_ELSE 1
> etc
>
>
> Now, your feature needs to turn on CONFIG_WANT_PAGE_DEBUG_FLAGS. Other
> debug features can do so as well.
>
> But we do need to ensure that CONFIG_WANT_PAGE_DEBUG_FLAGS reliably
> gets turned off when no debug features are enabling it! It would be
> sad if a developer were to enable your feature, then disable it, then
> run `oldconfig', then have a pageframe which contains an extra unused
> long. I don't trust the Kconfig system ;)

I've done it. Please see include/linux/page-debug-flags.h

From: Akinobu Mita <akinobu.mita@gmail.com>
Subject: [PATCH] generic debug pagealloc (-v4)

CONFIG_DEBUG_PAGEALLOC is now supported by x86, powerpc, sparc64, and s390.
This patch implements it for the rest of the architectures by filling the
pages with poison byte patterns after free_pages() and verifying the poison
patterns before alloc_pages().

This generic one cannot detect invalid page accesses immediately but invalid
read access may cause invalid dereference by poisoned memory and invalid write
access can be detected after a long delay.

* v4
- Introduce empty poison_highpage() and unpoison_highpage()
- Improve error messages for page corruption and dump_stack()
- Error messages ratelimiting
- Introduce debug_flage in struct page instead of bool poison

* v3
- Comments for poisoning highmem pages
- Sanity check for highmem pages
- Detect single bit error

* v2
- Skip poisoning for highmem pages
- Romove duplidate poison pattern checking

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: linux-arch@vger.kernel.org
Cc: linux-mm@kvack.org
---
arch/avr32/mm/fault.c | 18 -----
arch/powerpc/Kconfig | 3
arch/powerpc/Kconfig.debug | 1
arch/s390/Kconfig | 3
arch/s390/Kconfig.debug | 1
arch/sparc/Kconfig | 3
arch/sparc/Kconfig.debug | 3
arch/x86/Kconfig | 3
arch/x86/Kconfig.debug | 1
include/linux/mm_types.h | 5 +
include/linux/page-debug-flags.h | 30 +++++++++
include/linux/poison.h | 3
lib/Kconfig.debug | 1
mm/Kconfig.debug | 12 +++
mm/Makefile | 1
mm/debug-pagealloc.c | 129 +++++++++++++++++++++++++++++++++++++++
16 files changed, 198 insertions(+), 19 deletions(-)

Index: 2.6-poison/include/linux/poison.h
===================================================================
--- 2.6-poison.orig/include/linux/poison.h
+++ 2.6-poison/include/linux/poison.h
@@ -17,6 +17,9 @@
*/
#define TIMER_ENTRY_STATIC ((void *) 0x74737461)

+/********** mm/debug-pagealloc.c **********/
+#define PAGE_POISON 0xaa
+
/********** mm/slab.c **********/
/*
* Magic nums for obj red zoning.
Index: 2.6-poison/mm/debug-pagealloc.c
===================================================================
--- /dev/null
+++ 2.6-poison/mm/debug-pagealloc.c
@@ -0,0 +1,129 @@
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/page-debug-flags.h>
+#include <linux/poison.h>
+
+static inline void set_page_poison(struct page *page)
+{
+ __set_bit(PAGE_DEBUG_FLAG_POISON, &page->debug_flags);
+}
+
+static inline void clear_page_poison(struct page *page)
+{
+ __clear_bit(PAGE_DEBUG_FLAG_POISON, &page->debug_flags);
+}
+
+static inline bool page_poison(struct page *page)
+{
+ return test_bit(PAGE_DEBUG_FLAG_POISON, &page->debug_flags);
+}
+
+static void poison_highpage(struct page *page)
+{
+ /*
+ * Page poisoning for highmem pages is not implemented.
+ *
+ * This can be called from interrupt contexts.
+ * So we need to create a new kmap_atomic slot for this
+ * application and it will need interrupt protection.
+ */
+}
+
+static void poison_page(struct page *page)
+{
+ void *addr;
+
+ if (PageHighMem(page)) {
+ poison_highpage(page);
+ return;
+ }
+ set_page_poison(page);
+ addr = page_address(page);
+ memset(addr, PAGE_POISON, PAGE_SIZE);
+}
+
+static void poison_pages(struct page *page, int n)
+{
+ int i;
+
+ for (i = 0; i < n; i++)
+ poison_page(page + i);
+}
+
+static bool single_bit_flip(unsigned char a, unsigned char b)
+{
+ unsigned char error = a ^ b;
+
+ return error && !(error & (error - 1));
+}
+
+static void check_poison_mem(unsigned char *mem, size_t bytes)
+{
+ unsigned char *start;
+ unsigned char *end;
+
+ for (start = mem; start < mem + bytes; start++) {
+ if (*start != PAGE_POISON)
+ break;
+ }
+ if (start == mem + bytes)
+ return;
+
+ for (end = mem + bytes - 1; end > start; end--) {
+ if (*end != PAGE_POISON)
+ break;
+ }
+
+ if (!printk_ratelimit())
+ return;
+ else if (start == end && single_bit_flip(*start, PAGE_POISON))
+ printk(KERN_ERR "pagealloc: single bit error\n");
+ else
+ printk(KERN_ERR "pagealloc: memory corruption\n");
+
+ print_hex_dump(KERN_ERR, "", DUMP_PREFIX_ADDRESS, 16, 1, start,
+ end - start + 1, 1);
+ dump_stack();
+}
+
+static void unpoison_highpage(struct page *page)
+{
+ /*
+ * See comment in poison_highpage().
+ * Highmem pages should not be poisoned for now
+ */
+ BUG_ON(page_poison(page));
+}
+
+static void unpoison_page(struct page *page)
+{
+ if (PageHighMem(page)) {
+ unpoison_highpage(page);
+ return;
+ }
+ if (page_poison(page)) {
+ void *addr = page_address(page);
+
+ check_poison_mem(addr, PAGE_SIZE);
+ clear_page_poison(page);
+ }
+}
+
+static void unpoison_pages(struct page *page, int n)
+{
+ int i;
+
+ for (i = 0; i < n; i++)
+ unpoison_page(page + i);
+}
+
+void kernel_map_pages(struct page *page, int numpages, int enable)
+{
+ if (!debug_pagealloc_enabled)
+ return;
+
+ if (enable)
+ unpoison_pages(page, numpages);
+ else
+ poison_pages(page, numpages);
+}
Index: 2.6-poison/mm/Kconfig.debug
===================================================================
--- /dev/null
+++ 2.6-poison/mm/Kconfig.debug
@@ -0,0 +1,12 @@
+config WANT_PAGE_DEBUG_FLAGS
+ bool
+
+config PAGE_POISONING
+ bool "Debug page memory allocations"
+ depends on !ARCH_SUPPORTS_DEBUG_PAGEALLOC
+ select DEBUG_PAGEALLOC
+ select WANT_PAGE_DEBUG_FLAGS
+ help
+ Fill the pages with poison patterns after free_pages() and verify
+ the patterns before alloc_pages(). This results in a large slowdown,
+ but helps to find certain types of memory corruptions.
Index: 2.6-poison/mm/Makefile
===================================================================
--- 2.6-poison.orig/mm/Makefile
+++ 2.6-poison/mm/Makefile
@@ -33,3 +33,4 @@ obj-$(CONFIG_MIGRATION) += migrate.o
obj-$(CONFIG_SMP) += allocpercpu.o
obj-$(CONFIG_QUICKLIST) += quicklist.o
obj-$(CONFIG_CGROUP_MEM_RES_CTLR) += memcontrol.o page_cgroup.o
+obj-$(CONFIG_PAGE_POISONING) += debug-pagealloc.o
Index: 2.6-poison/lib/Kconfig.debug
===================================================================
--- 2.6-poison.orig/lib/Kconfig.debug
+++ 2.6-poison/lib/Kconfig.debug
@@ -796,6 +796,7 @@ config SYSCTL_SYSCALL_CHECK
to properly maintain and use. This enables checks that help
you to keep things correct.

+source mm/Kconfig.debug
source kernel/trace/Kconfig

config PROVIDE_OHCI1394_DMA_INIT
Index: 2.6-poison/arch/powerpc/Kconfig.debug
===================================================================
--- 2.6-poison.orig/arch/powerpc/Kconfig.debug
+++ 2.6-poison/arch/powerpc/Kconfig.debug
@@ -30,6 +30,7 @@ config DEBUG_STACK_USAGE
config DEBUG_PAGEALLOC
bool "Debug page memory allocations"
depends on DEBUG_KERNEL && !HIBERNATION
+ depends on ARCH_SUPPORTS_DEBUG_PAGEALLOC
help
Unmap pages from the kernel linear mapping after free_pages().
This results in a large slowdown, but helps to find certain types
Index: 2.6-poison/arch/s390/Kconfig.debug
===================================================================
--- 2.6-poison.orig/arch/s390/Kconfig.debug
+++ 2.6-poison/arch/s390/Kconfig.debug
@@ -9,6 +9,7 @@ source "lib/Kconfig.debug"
config DEBUG_PAGEALLOC
bool "Debug page memory allocations"
depends on DEBUG_KERNEL
+ depends on ARCH_SUPPORTS_DEBUG_PAGEALLOC
help
Unmap pages from the kernel linear mapping after free_pages().
This results in a slowdown, but helps to find certain types of
Index: 2.6-poison/arch/sparc/Kconfig.debug
===================================================================
--- 2.6-poison.orig/arch/sparc/Kconfig.debug
+++ 2.6-poison/arch/sparc/Kconfig.debug
@@ -24,7 +24,8 @@ config STACK_DEBUG

config DEBUG_PAGEALLOC
bool "Debug page memory allocations"
- depends on SPARC64 && DEBUG_KERNEL && !HIBERNATION
+ depends on DEBUG_KERNEL && !HIBERNATION
+ depends on ARCH_SUPPORTS_DEBUG_PAGEALLOC
help
Unmap pages from the kernel linear mapping after free_pages().
This results in a large slowdown, but helps to find certain types
Index: 2.6-poison/arch/x86/Kconfig
===================================================================
--- 2.6-poison.orig/arch/x86/Kconfig
+++ 2.6-poison/arch/x86/Kconfig
@@ -160,6 +160,9 @@ config AUDIT_ARCH
config ARCH_SUPPORTS_OPTIMIZED_INLINING
def_bool y

+config ARCH_SUPPORTS_DEBUG_PAGEALLOC
+ def_bool y
+
# Use the generic interrupt handling code in kernel/irq/:
config GENERIC_HARDIRQS
bool
Index: 2.6-poison/arch/x86/Kconfig.debug
===================================================================
--- 2.6-poison.orig/arch/x86/Kconfig.debug
+++ 2.6-poison/arch/x86/Kconfig.debug
@@ -75,6 +75,7 @@ config DEBUG_STACK_USAGE
config DEBUG_PAGEALLOC
bool "Debug page memory allocations"
depends on DEBUG_KERNEL
+ depends on ARCH_SUPPORTS_DEBUG_PAGEALLOC
help
Unmap pages from the kernel linear mapping after free_pages().
This results in a large slowdown, but helps to find certain types
Index: 2.6-poison/arch/powerpc/Kconfig
===================================================================
--- 2.6-poison.orig/arch/powerpc/Kconfig
+++ 2.6-poison/arch/powerpc/Kconfig
@@ -227,6 +227,9 @@ config PPC_OF_PLATFORM_PCI
depends on PPC64 # not supported on 32 bits yet
default n

+config ARCH_SUPPORTS_DEBUG_PAGEALLOC
+ def_bool y
+
source "init/Kconfig"

source "kernel/Kconfig.freezer"
Index: 2.6-poison/arch/sparc/Kconfig
===================================================================
--- 2.6-poison.orig/arch/sparc/Kconfig
+++ 2.6-poison/arch/sparc/Kconfig
@@ -124,6 +124,9 @@ config ARCH_NO_VIRT_TO_BUS
config OF
def_bool y

+config ARCH_SUPPORTS_DEBUG_PAGEALLOC
+ def_bool y if SPARC64
+
source "init/Kconfig"

source "kernel/Kconfig.freezer"
Index: 2.6-poison/arch/avr32/mm/fault.c
===================================================================
--- 2.6-poison.orig/arch/avr32/mm/fault.c
+++ 2.6-poison/arch/avr32/mm/fault.c
@@ -250,21 +250,3 @@ asmlinkage void do_bus_error(unsigned lo
dump_dtlb();
die("Bus Error", regs, SIGKILL);
}
-
-/*
- * This functionality is currently not possible to implement because
- * we're using segmentation to ensure a fixed mapping of the kernel
- * virtual address space.
- *
- * It would be possible to implement this, but it would require us to
- * disable segmentation at startup and load the kernel mappings into
- * the TLB like any other pages. There will be lots of trickery to
- * avoid recursive invocation of the TLB miss handler, though...
- */
-#ifdef CONFIG_DEBUG_PAGEALLOC
-void kernel_map_pages(struct page *page, int numpages, int enable)
-{
-
-}
-EXPORT_SYMBOL(kernel_map_pages);
-#endif
Index: 2.6-poison/arch/s390/Kconfig
===================================================================
--- 2.6-poison.orig/arch/s390/Kconfig
+++ 2.6-poison/arch/s390/Kconfig
@@ -72,6 +72,9 @@ config PGSTE
config VIRT_CPU_ACCOUNTING
def_bool y

+config ARCH_SUPPORTS_DEBUG_PAGEALLOC
+ def_bool y
+
mainmenu "Linux Kernel Configuration"

config S390
Index: 2.6-poison/include/linux/mm_types.h
===================================================================
--- 2.6-poison.orig/include/linux/mm_types.h
+++ 2.6-poison/include/linux/mm_types.h
@@ -11,6 +11,7 @@
#include <linux/rwsem.h>
#include <linux/completion.h>
#include <linux/cpumask.h>
+#include <linux/page-debug-flags.h>
#include <asm/page.h>
#include <asm/mmu.h>

@@ -94,6 +95,10 @@ struct page {
void *virtual; /* Kernel virtual address (NULL if
not kmapped, ie. highmem) */
#endif /* WANT_PAGE_VIRTUAL */
+
+#ifdef CONFIG_WANT_PAGE_DEBUG_FLAGS
+ unsigned long debug_flags; /* Use atomic bitops on this */
+#endif
};

/*
Index: 2.6-poison/include/linux/page-debug-flags.h
===================================================================
--- /dev/null
+++ 2.6-poison/include/linux/page-debug-flags.h
@@ -0,0 +1,30 @@
+#ifndef LINUX_PAGE_DEBUG_FLAGS_H
+#define LINUX_PAGE_DEBUG_FLAGS_H
+
+/*
+ * page->debug_flags bits:
+ *
+ * PAGE_DEBUG_FLAG_POISON is set for poisoned pages. This is used to
+ * implement generic debug pagealloc feature. The pages are filled with
+ * poison patterns and set this flag after free_pages(). The poisoned
+ * pages are verified whether the patterns are not corrupted and clear
+ * the flag before alloc_pages().
+ */
+
+enum page_debug_flags {
+ PAGE_DEBUG_FLAG_POISON, /* Page is poisoned */
+};
+
+/*
+ * Ensure that CONFIG_WANT_PAGE_DEBUG_FLAGS reliably
+ * gets turned off when no debug features are enabling it!
+ */
+
+#ifdef CONFIG_WANT_PAGE_DEBUG_FLAGS
+#if !defined(CONFIG_PAGE_POISONING) \
+/* && !defined(CONFIG_PAGE_DEBUG_SOMETHING_ELSE) && ... */
+#error WANT_PAGE_DEBUG_FLAGS is turned on with no debug features!
+#endif
+#endif /* CONFIG_WANT_PAGE_DEBUG_FLAGS */
+
+#endif /* LINUX_PAGE_DEBUG_FLAGS_H */