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SubjectRe: [PATCH -tip v3 05/11] kcsan: Remove 'noinline' from __no_kcsan_or_inline
On Thu, May 21, 2020 at 04:20:41PM +0200, Marco Elver wrote:
> Some compilers incorrectly inline small __no_kcsan functions, which then
> results in instrumenting the accesses. For this reason, the 'noinline'
> attribute was added to __no_kcsan_or_inline. All known versions of GCC
> are affected by this. Supported version of Clang are unaffected, and
> never inlines a no_sanitize function.
>
> However, the attribute 'noinline' in __no_kcsan_or_inline causes
> unexpected code generation in functions that are __no_kcsan and call a
> __no_kcsan_or_inline function.
>
> In certain situations it is expected that the __no_kcsan_or_inline
> function is actually inlined by the __no_kcsan function, and *no* calls
> are emitted. By removing the 'noinline' attribute we give the compiler
> the ability to inline and generate the expected code in __no_kcsan
> functions.


Doesn't this mean we can do the below?

---
Documentation/dev-tools/kcsan.rst | 6 ------
arch/x86/include/asm/bitops.h | 6 +-----
include/linux/compiler_types.h | 14 ++++----------
kernel/kcsan/kcsan-test.c | 4 ++--
4 files changed, 7 insertions(+), 23 deletions(-)

diff --git a/Documentation/dev-tools/kcsan.rst b/Documentation/dev-tools/kcsan.rst
index ce4bbd918648..b38379f06194 100644
--- a/Documentation/dev-tools/kcsan.rst
+++ b/Documentation/dev-tools/kcsan.rst
@@ -114,12 +114,6 @@ functions, compilation units, or entire subsystems. For static blacklisting,
To dynamically limit for which functions to generate reports, see the
`DebugFS interface`_ blacklist/whitelist feature.

- For ``__always_inline`` functions, replace ``__always_inline`` with
- ``__no_kcsan_or_inline`` (which implies ``__always_inline``)::
-
- static __no_kcsan_or_inline void foo(void) {
- ...
-
* To disable data race detection for a particular compilation unit, add to the
``Makefile``::

diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h
index 35460fef39b8..0367efdc5b7a 100644
--- a/arch/x86/include/asm/bitops.h
+++ b/arch/x86/include/asm/bitops.h
@@ -201,12 +201,8 @@ arch_test_and_change_bit(long nr, volatile unsigned long *addr)
return GEN_BINARY_RMWcc(LOCK_PREFIX __ASM_SIZE(btc), *addr, c, "Ir", nr);
}

-static __no_kcsan_or_inline bool constant_test_bit(long nr, const volatile unsigned long *addr)
+static __always_inline bool constant_test_bit(long nr, const volatile unsigned long *addr)
{
- /*
- * Because this is a plain access, we need to disable KCSAN here to
- * avoid double instrumentation via instrumented bitops.
- */
return ((1UL << (nr & (BITS_PER_LONG-1))) &
(addr[nr >> _BITOPS_LONG_SHIFT])) != 0;
}
diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index 4e4982d6f3b0..6a2c0f857ac3 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -118,10 +118,6 @@ struct ftrace_likely_data {
#define notrace __attribute__((__no_instrument_function__))
#endif

-/* Section for code which can't be instrumented at all */
-#define noinstr \
- noinline notrace __attribute((__section__(".noinstr.text")))
-
/*
* it doesn't make sense on ARM (currently the only user of __naked)
* to trace naked functions because then mcount is called without
@@ -192,17 +188,15 @@ struct ftrace_likely_data {
#endif

#define __no_kcsan __no_sanitize_thread
-#ifdef __SANITIZE_THREAD__
-# define __no_kcsan_or_inline __no_kcsan notrace __maybe_unused
-# define __no_sanitize_or_inline __no_kcsan_or_inline
-#else
-# define __no_kcsan_or_inline __always_inline
-#endif

#ifndef __no_sanitize_or_inline
#define __no_sanitize_or_inline __always_inline
#endif

+/* Section for code which can't be instrumented at all */
+#define noinstr \
+ noinline notrace __attribute((__section__(".noinstr.text"))) __no_kcsan
+
#endif /* __KERNEL__ */

#endif /* __ASSEMBLY__ */
diff --git a/kernel/kcsan/kcsan-test.c b/kernel/kcsan/kcsan-test.c
index a8c11506dd2a..374263ddffe2 100644
--- a/kernel/kcsan/kcsan-test.c
+++ b/kernel/kcsan/kcsan-test.c
@@ -43,7 +43,7 @@ static struct {
};

/* Setup test checking loop. */
-static __no_kcsan_or_inline void
+static __no_kcsan inline void
begin_test_checks(void (*func1)(void), void (*func2)(void))
{
kcsan_disable_current();
@@ -60,7 +60,7 @@ begin_test_checks(void (*func1)(void), void (*func2)(void))
}

/* End test checking loop. */
-static __no_kcsan_or_inline bool
+static __no_kcsan inline bool
end_test_checks(bool stop)
{
if (!stop && time_before(jiffies, end_time)) {
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