[PATCH] atomics: fix atomic64_{read_acquire,set_release} fallbacks
From: Mark Rutland
Date: Thu Feb 03 2022 - 09:38:59 EST
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.
For the example above this works as expected on 32-bit, e.g.
| <test_atomic64>:
| dmb ish
| mov r2, #5
| mov r3, #0
| strd r2, [r0]
| ldrd r2, [r0]
| dmb ish
| bx lr
... and also on 64-bit, e.g.
| <test_atomic64>:
| bti c
| paciasp
| mov x1, #0x5
| stlr x1, [x0]
| ldar x0, [x0]
| autiasp
| ret
Reported-by: Arnd Bergmann <arnd@xxxxxxxx>
Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
---
include/linux/atomic/atomic-arch-fallback.h | 38 ++++++++++++++++++---
scripts/atomic/fallbacks/read_acquire | 11 +++++-
scripts/atomic/fallbacks/set_release | 7 +++-
3 files changed, 49 insertions(+), 7 deletions(-)
diff --git a/include/linux/atomic/atomic-arch-fallback.h b/include/linux/atomic/atomic-arch-fallback.h
index a3dba31df01e..8dfb03317f2a 100644
--- a/include/linux/atomic/atomic-arch-fallback.h
+++ b/include/linux/atomic/atomic-arch-fallback.h
@@ -151,7 +151,16 @@
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
@@ -160,7 +169,12 @@ arch_atomic_read_acquire(const atomic_t *v)
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
@@ -1258,7 +1272,16 @@ arch_atomic_dec_if_positive(atomic_t *v)
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_atomic_read(v);
+ __atomic_acquire_fence();
+ }
+
+ return ret;
}
#define arch_atomic64_read_acquire arch_atomic64_read_acquire
#endif
@@ -1267,7 +1290,12 @@ arch_atomic64_read_acquire(const atomic64_t *v)
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_atomic_set(v, i);
+ }
}
#define arch_atomic64_set_release arch_atomic64_set_release
#endif
@@ -2358,4 +2386,4 @@ arch_atomic64_dec_if_positive(atomic64_t *v)
#endif
#endif /* _LINUX_ATOMIC_FALLBACK_H */
-// cca554917d7ea73d5e3e7397dd70c484cad9b2c4
+// ba488b6398359cb776d457971f30cef78d0d36dc
diff --git a/scripts/atomic/fallbacks/read_acquire b/scripts/atomic/fallbacks/read_acquire
index 803ba7561076..7b8b87143c0c 100755
--- a/scripts/atomic/fallbacks/read_acquire
+++ b/scripts/atomic/fallbacks/read_acquire
@@ -2,6 +2,15 @@ cat <<EOF
static __always_inline ${ret}
arch_${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;
}
EOF
diff --git a/scripts/atomic/fallbacks/set_release b/scripts/atomic/fallbacks/set_release
index 86ede759f24e..5f692db3ce29 100755
--- a/scripts/atomic/fallbacks/set_release
+++ b/scripts/atomic/fallbacks/set_release
@@ -2,6 +2,11 @@ cat <<EOF
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
--
2.30.2