The patch titled
atomic: detect and warn on atomic_inc/atomic_dec wrapping around
has been added to the -mm tree. Its filename is
atomic-detect-and-warn-on-atomic_inc-atomic_dec-wrapping-around.patch
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find
out what to do about this
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: atomic: detect and warn on atomic_inc/atomic_dec wrapping around
From: Nikanth Karthikesan <knikanth@xxxxxxxxxx>
Add a debug option to detect and warn when the 32-bit atomic_t overflows
during atomic_inc and atomic_dec.
We expect that overflow and underflow of an atomic_t is usually a bug.
There was a patch of this nature in -mm for a long time and it never
triggered false positives and it did find a couple of real bugs.
The option is default-y for now. It will have a fairly nasty impact on
.text size so we may decide to switch it to default-n prior to a kernel
release.
Signed-off-by: Nikanth Karthikesan <knikanth@xxxxxxx>
Acked-by: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/x86/Kconfig | 1
arch/x86/include/asm/atomic_32.h | 8 ++---
arch/x86/include/asm/atomic_64.h | 8 ++---
include/asm-generic/atomic.h | 40 +++++++++++++++++++++++++++--
lib/Kconfig.debug | 11 +++++++
5 files changed, 58 insertions(+), 10 deletions(-)
diff -puN arch/x86/Kconfig~atomic-detect-and-warn-on-atomic_inc-atomic_dec-wrapping-around arch/x86/Kconfig
--- a/arch/x86/Kconfig~atomic-detect-and-warn-on-atomic_inc-atomic_dec-wrapping-around
+++ a/arch/x86/Kconfig
@@ -46,6 +46,7 @@ config X86
select HAVE_KERNEL_GZIP
select HAVE_KERNEL_BZIP2
select HAVE_KERNEL_LZMA
+ select HAVE_ARCH_DEBUG_ATOMIC
config ARCH_DEFCONFIG
string
diff -puN arch/x86/include/asm/atomic_32.h~atomic-detect-and-warn-on-atomic_inc-atomic_dec-wrapping-around arch/x86/include/asm/atomic_32.h
--- a/arch/x86/include/asm/atomic_32.h~atomic-detect-and-warn-on-atomic_inc-atomic_dec-wrapping-around
+++ a/arch/x86/include/asm/atomic_32.h
@@ -78,24 +78,24 @@ static inline int atomic_sub_and_test(in
}
/**
- * atomic_inc - increment atomic variable
+ * raw_atomic_inc - increment atomic variable
* @v: pointer of type atomic_t
*
* Atomically increments @v by 1.
*/
-static inline void atomic_inc(atomic_t *v)
+static inline void raw_atomic_inc(atomic_t *v)
{
asm volatile(LOCK_PREFIX "incl %0"
: "+m" (v->counter));
}
/**
- * atomic_dec - decrement atomic variable
+ * raw_atomic_dec - decrement atomic variable
* @v: pointer of type atomic_t
*
* Atomically decrements @v by 1.
*/
-static inline void atomic_dec(atomic_t *v)
+static inline void raw_atomic_dec(atomic_t *v)
{
asm volatile(LOCK_PREFIX "decl %0"
: "+m" (v->counter));
diff -puN arch/x86/include/asm/atomic_64.h~atomic-detect-and-warn-on-atomic_inc-atomic_dec-wrapping-around arch/x86/include/asm/atomic_64.h
--- a/arch/x86/include/asm/atomic_64.h~atomic-detect-and-warn-on-atomic_inc-atomic_dec-wrapping-around
+++ a/arch/x86/include/asm/atomic_64.h
@@ -77,12 +77,12 @@ static inline int atomic_sub_and_test(in
}
/**
- * atomic_inc - increment atomic variable
+ * raw_atomic_inc - increment atomic variable
* @v: pointer of type atomic_t
*
* Atomically increments @v by 1.
*/
-static inline void atomic_inc(atomic_t *v)
+static inline void raw_atomic_inc(atomic_t *v)
{
asm volatile(LOCK_PREFIX "incl %0"
: "=m" (v->counter)
@@ -90,12 +90,12 @@ static inline void atomic_inc(atomic_t *
}
/**
- * atomic_dec - decrement atomic variable
+ * raw_atomic_dec - decrement atomic variable
* @v: pointer of type atomic_t
*
* Atomically decrements @v by 1.
*/
-static inline void atomic_dec(atomic_t *v)
+static inline void raw_atomic_dec(atomic_t *v)
{
asm volatile(LOCK_PREFIX "decl %0"
: "=m" (v->counter)
diff -puN include/asm-generic/atomic.h~atomic-detect-and-warn-on-atomic_inc-atomic_dec-wrapping-around include/asm-generic/atomic.h
--- a/include/asm-generic/atomic.h~atomic-detect-and-warn-on-atomic_inc-atomic_dec-wrapping-around
+++ a/include/asm-generic/atomic.h
@@ -4,15 +4,51 @@
* Copyright (C) 2005 Silicon Graphics, Inc.
* Christoph Lameter
*
- * Allows to provide arch independent atomic definitions without the need to
- * edit all arch specific atomic.h files.
*/
+#include <linux/kernel.h>
#include <asm/types.h>
+#include <asm/bug.h>
+
+
+/**
+ * atomic_inc - increment atomic variable
+ * @v: pointer of type atomic_t
+ *
+ * Atomically increments @v by 1.
+ */
+static inline void atomic_inc(atomic_t *v)
+{
+#ifdef CONFIG_ENABLE_WARN_ATOMIC_INC_WRAP
+ WARN_ONCE((atomic_read(v) > (INT_MAX / 2)),
+ KERN_ERR "atomic inc overflow!");
+#endif
+ raw_atomic_inc(v);
+}
+
+/**
+ * atomic_dec - decrement atomic variable
+ * @v: pointer of type atomic_t
+ *
+ * Atomically decrements @v by 1.
+ */
+static inline void atomic_dec(atomic_t *v)
+{
+#ifdef CONFIG_ENABLE_WARN_ATOMIC_INC_WRAP
+ WARN_ONCE((atomic_read(v) < (INT_MIN / 2)),
+ KERN_ERR "atomic dec underflow!");
+#endif
+ raw_atomic_dec(v);
+
+}
+
/*
* Suppport for atomic_long_t
*
+ * Allows to provide arch independent atomic definitions without the need to
+ * edit all arch specific atomic.h files.
+ *
* Casts for parameters are avoided for existing atomic functions in order to
* avoid issues with cast-as-lval under gcc 4.x and other limitations that the
* macros of a platform may have.
diff -puN lib/Kconfig.debug~atomic-detect-and-warn-on-atomic_inc-atomic_dec-wrapping-around lib/Kconfig.debug
--- a/lib/Kconfig.debug~atomic-detect-and-warn-on-atomic_inc-atomic_dec-wrapping-around
+++ a/lib/Kconfig.debug
@@ -17,6 +17,17 @@ config ENABLE_WARN_DEPRECATED
Disable this to suppress the "warning: 'foo' is deprecated
(declared at kernel/power/somefile.c:1234)" messages.
+config HAVE_ARCH_DEBUG_ATOMIC
+ bool
+
+config ENABLE_WARN_ATOMIC_INC_WRAP
+ bool "Enable warning on atomic_inc()/atomic_dec() wrap"
+ depends on HAVE_ARCH_DEBUG_ATOMIC
+ default y
+ help
+ Enable printing a warning when atomic_inc() or atomic_dec()
+ operation wraps around the 32-bit value.
+
config ENABLE_MUST_CHECK
bool "Enable __must_check logic"
default y
_
Patches currently in -mm which might be from knikanth@xxxxxxxxxx are
block-prevent-possible-io_context-refcount-overflow.patch
atomic-detect-and-warn-on-atomic_inc-atomic_dec-wrapping-around.patch
--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
