atomics: Fix atomic64_{read_acquire,set_release} fallbacks

Arnd reports that on 32-bit architectures, the fallbacks for atomic64_read_acquire() and atomic64_set_release() are broken as they use smp_load_acquire() and smp_store_release() respectively, which do not work on types larger than the native word size. Since those contain compiletime_assert_atomic_type(), any attempt to use those fallbacks will result in a build-time error. e.g. with the following added to arch/arm/kernel/setup.c: | void test_atomic64(atomic64_t *v) | { | atomic64_set_release(v, 5); | atomic64_read_acquire(v); | } The compiler will complain as follows: | In file included from <command-line>: | In function 'arch_atomic64_set_release', | inlined from 'test_atomic64' at ./include/linux/atomic/atomic-instrumented.h:669:2: | ././include/linux/compiler_types.h:346:38: error: call to '__compiletime_assert_9' declared with attribute error: Need native word sized stores/loads for atomicity. | 346 | _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__) | | ^ | ././include/linux/compiler_types.h:327:4: note: in definition of macro '__compiletime_assert' | 327 | prefix ## suffix(); \ | | ^~~~~~ | ././include/linux/compiler_types.h:346:2: note: in expansion of macro '_compiletime_assert' | 346 | _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__) | | ^~~~~~~~~~~~~~~~~~~ | ././include/linux/compiler_types.h:349:2: note: in expansion of macro 'compiletime_assert' | 349 | compiletime_assert(__native_word(t), \ | | ^~~~~~~~~~~~~~~~~~ | ./include/asm-generic/barrier.h:133:2: note: in expansion of macro 'compiletime_assert_atomic_type' | 133 | compiletime_assert_atomic_type(*p); \ | | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | ./include/asm-generic/barrier.h:164:55: note: in expansion of macro '__smp_store_release' | 164 | #define smp_store_release(p, v) do { kcsan_release(); __smp_store_release(p, v); } while (0) | | ^~~~~~~~~~~~~~~~~~~ | ./include/linux/atomic/atomic-arch-fallback.h:1270:2: note: in expansion of macro 'smp_store_release' | 1270 | smp_store_release(&(v)->counter, i); | | ^~~~~~~~~~~~~~~~~ | make[2]: *** [scripts/Makefile.build:288: arch/arm/kernel/setup.o] Error 1 | make[1]: *** [scripts/Makefile.build:550: arch/arm/kernel] Error 2 | make: *** [Makefile:1831: arch/arm] Error 2 Fix this by only using smp_load_acquire() and smp_store_release() for native atomic types, and otherwise falling back to the regular barriers necessary for acquire/release semantics, as we do in the more generic acquire and release fallbacks. Since the fallback templates are used to generate the atomic64_*() and atomic_*() operations, the __native_word() check is added to both. For the atomic_*() operations, which are always 32-bit, the __native_word() check is redundant but not harmful, as it is always true. For the example above this works as expected on 32-bit, e.g. for arm multi_v7_defconfig: | <test_atomic64>: | push {r4, r5} | dmb ish | pldw [r0] | mov r2, #5 | mov r3, #0 | ldrexd r4, [r0] | strexd r4, r2, [r0] | teq r4, #0 | bne 484 <test_atomic64+0x14> | ldrexd r2, [r0] | dmb ish | pop {r4, r5} | bx lr ... and also on 64-bit, e.g. for arm64 defconfig: | <test_atomic64>: | bti c | paciasp | mov x1, #0x5 | stlr x1, [x0] | ldar x0, [x0] | autiasp | ret

Mark Rutland committed 4 years ago

Commit dc1b4df1 parent c441e933 files · +49 −7Browse files

Unified · Split

3 files

include/linux/atomic/atomic-arch-fallback.h +33 −5
scripts/atomic/fallbacks/read_acquire +10 −1
scripts/atomic/fallbacks/set_release +6 −1

include/linux/atomic/atomic-arch-fallback.h+33−5

 static __always_inline int
 arch_atomic_read_acquire(const atomic_t *v)
 {
-	return smp_load_acquire(&(v)->counter);
+	int ret;
+	if (__native_word(atomic_t)) {
+		ret = smp_load_acquire(&(v)->counter);
+	} else {
+		ret = arch_atomic_read(v);
+		__atomic_acquire_fence();
+	}
+	return ret;
 }
 #define arch_atomic_read_acquire arch_atomic_read_acquire
 #endif
 static __always_inline void
 arch_atomic_set_release(atomic_t *v, int i)
 {
-	smp_store_release(&(v)->counter, i);
+	if (__native_word(atomic_t)) {
+		smp_store_release(&(v)->counter, i);
+	} else {
+		__atomic_release_fence();
+		arch_atomic_set(v, i);
+	}
 }
 #define arch_atomic_set_release arch_atomic_set_release
 #endif
 static __always_inline s64
 arch_atomic64_read_acquire(const atomic64_t *v)
 {
-	return smp_load_acquire(&(v)->counter);
+	s64 ret;
+	if (__native_word(atomic64_t)) {
+		ret = smp_load_acquire(&(v)->counter);
+	} else {
+		ret = arch_atomic64_read(v);
+		__atomic_acquire_fence();
+	}
+	return ret;
 }
 #define arch_atomic64_read_acquire arch_atomic64_read_acquire
 #endif
 static __always_inline void
 arch_atomic64_set_release(atomic64_t *v, s64 i)
 {
-	smp_store_release(&(v)->counter, i);
+	if (__native_word(atomic64_t)) {
+		smp_store_release(&(v)->counter, i);
+	} else {
+		__atomic_release_fence();
+		arch_atomic64_set(v, i);
+	}
 }
 #define arch_atomic64_set_release arch_atomic64_set_release
 #endif
 #endif
 #endif /* _LINUX_ATOMIC_FALLBACK_H */
-// cca554917d7ea73d5e3e7397dd70c484cad9b2c4
+// 8e2cc06bc0d2c0967d2f8424762bd48555ee40ae

scripts/atomic/fallbacks/read_acquire+10−1

@@ -2,6 +2,15 @@ cat <<EOF · 1 unmodified line
2	static __always_inline ${ret}	2	static __always_inline ${ret}
3	arch_${atomic}_read_acquire(const ${atomic}_t *v)	3	arch_${atomic}_read_acquire(const ${atomic}_t *v)
4	{	4	{
5	return smp_load_acquire(&(v)->counter);	5	${int} ret;
		6
		7	if (__native_word(${atomic}_t)) {
		8	ret = smp_load_acquire(&(v)->counter);
		9	} else {
		10	ret = arch_${atomic}_read(v);
		11	__atomic_acquire_fence();
		12	}
		13
		14	return ret;
6	}	15	}
7	EOF	16	EOF

scripts/atomic/fallbacks/set_release+6−1

 static __always_inline void
 arch_${atomic}_set_release(${atomic}_t *v, ${int} i)
 {
-	smp_store_release(&(v)->counter, i);
+	if (__native_word(${atomic}_t)) {
+		smp_store_release(&(v)->counter, i);
+	} else {
+		__atomic_release_fence();
+		arch_${atomic}_set(v, i);
+	}
 }
 EOF