From: Mark Rutland mark.rutland@arm.com
[ Upstream commit dc1b4df09acdca7a89806b28f235cd6d8dcd3d24 ]
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
Reported-by: Arnd Bergmann arnd@arndb.de Signed-off-by: Mark Rutland mark.rutland@arm.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Ard Biesheuvel ardb@kernel.org Reviewed-by: Boqun Feng boqun.feng@gmail.com Link: https://lore.kernel.org/r/20220207101943.439825-1-mark.rutland@arm.com Signed-off-by: Sasha Levin sashal@kernel.org --- 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..6db58d180866 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_atomic64_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_atomic64_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 +// 8e2cc06bc0d2c0967d2f8424762bd48555ee40ae diff --git a/scripts/atomic/fallbacks/read_acquire b/scripts/atomic/fallbacks/read_acquire index 803ba7561076..a0ea1d26e6b2 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_${atomic}_read(v); + __atomic_acquire_fence(); + } + + return ret; } EOF diff --git a/scripts/atomic/fallbacks/set_release b/scripts/atomic/fallbacks/set_release index 86ede759f24e..05cdb7f42477 100755 --- a/scripts/atomic/fallbacks/set_release +++ b/scripts/atomic/fallbacks/set_release @@ -2,6 +2,11 @@ cat <<EOF static __always_inline void arch_${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