linux-kernel - [tip: locking/kcsan] locking/barriers: Use '__unqual_scalar

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Date:   Tue, 12 May 2020 14:36:55 -0000
From:   "tip-bot2 for Will Deacon" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Will Deacon <will@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>, x86 <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [tip: locking/kcsan] locking/barriers: Use '__unqual_scalar_typeof'
 for load-acquire macros

The following commit has been merged into the locking/kcsan branch of tip:

Commit-ID:     0229d80867ef27b3e41585a784d5f78695a58f95
Gitweb:        https://git.kernel.org/tip/0229d80867ef27b3e41585a784d5f78695a58f95
Author:        Will Deacon <will@...nel.org>
AuthorDate:    Mon, 11 May 2020 21:41:45 +01:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Tue, 12 May 2020 11:04:15 +02:00

locking/barriers: Use '__unqual_scalar_typeof' for load-acquire macros

Passing volatile-qualified pointers to the asm-generic implementations of
the load-acquire macros results in a re-load from the stack due to the
temporary result variable inheriting the volatile semantics thanks to the
use of 'typeof()'.

Define these temporary variables using 'unqual_scalar_typeof' to drop
the volatile qualifier in the case that they are scalar types.

Signed-off-by: Will Deacon <will@...nel.org>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Arnd Bergmann <arnd@...db.de>
Link: https://lkml.kernel.org/r/20200511204150.27858-14-will@kernel.org

---
 include/asm-generic/barrier.h | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h
index 85b28eb..2eacaf7 100644
--- a/include/asm-generic/barrier.h
+++ b/include/asm-generic/barrier.h
@@ -128,10 +128,10 @@ do {									\
 #ifndef __smp_load_acquire
 #define __smp_load_acquire(p)						\
 ({									\
-	typeof(*p) ___p1 = READ_ONCE(*p);				\
+	__unqual_scalar_typeof(*p) ___p1 = READ_ONCE(*p);		\
 	compiletime_assert_atomic_type(*p);				\
 	__smp_mb();							\
-	___p1;								\
+	(typeof(*p))___p1;						\
 })
 #endif
 
@@ -183,10 +183,10 @@ do {									\
 #ifndef smp_load_acquire
 #define smp_load_acquire(p)						\
 ({									\
-	typeof(*p) ___p1 = READ_ONCE(*p);				\
+	__unqual_scalar_typeof(*p) ___p1 = READ_ONCE(*p);		\
 	compiletime_assert_atomic_type(*p);				\
 	barrier();							\
-	___p1;								\
+	(typeof(*p))___p1;						\
 })
 #endif
 
@@ -229,14 +229,14 @@ do {									\
 #ifndef smp_cond_load_relaxed
 #define smp_cond_load_relaxed(ptr, cond_expr) ({		\
 	typeof(ptr) __PTR = (ptr);				\
-	typeof(*ptr) VAL;					\
+	__unqual_scalar_typeof(*ptr) VAL;			\
 	for (;;) {						\
 		VAL = READ_ONCE(*__PTR);			\
 		if (cond_expr)					\
 			break;					\
 		cpu_relax();					\
 	}							\
-	VAL;							\
+	(typeof(*ptr))VAL;					\
 })
 #endif
 
@@ -250,10 +250,10 @@ do {									\
  */
 #ifndef smp_cond_load_acquire
 #define smp_cond_load_acquire(ptr, cond_expr) ({		\
-	typeof(*ptr) _val;					\
+	__unqual_scalar_typeof(*ptr) _val;			\
 	_val = smp_cond_load_relaxed(ptr, cond_expr);		\
 	smp_acquire__after_ctrl_dep();				\
-	_val;							\
+	(typeof(*ptr))_val;					\
 })
 #endif