From 1fc7e593e2028f5e0949a67050b4c15167698a4f Mon Sep 17 00:00:00 2001 From: Leo Yan Date: Mon, 9 Aug 2021 19:14:04 +0800 Subject: [PATCH] perf auxtrace: Drop legacy __sync functions MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit The main purpose for using __sync built-in functions is to support compat mode for 32-bit perf with 64-bit kernel. But using these built-in functions might cause potential issues. __sync functions originally support Intel Itanium processoer [1] but it cannot promise to support all 32-bit archs. Now these functions have become the legacy functions. Considering __sync functions cannot really fix the 64-bit value atomicity on 32-bit archs, thus this patch drops __sync functions. Credits to Peter for detailed analysis. [1] https://gcc.gnu.org/onlinedocs/gcc/_005f_005fsync-Builtins.html#g_t_005f_005fsync-Builtins Suggested-by: Peter Zijlstra Signed-off-by: Leo Yan Cc: Adrian Hunter Cc: Alexander Shishkin Cc: Alexei Starovoitov Cc: Andi Kleen Cc: Andrii Nakryiko Cc: Borislav Petkov Cc: Daniel Díaz Cc: Frank Ch. Eigler Cc: H. Peter Anvin Cc: Jiri Olsa Cc: Mark Rutland Cc: Mathieu Poirier Cc: Michael Petlan Cc: Mike Leach Cc: Namhyung Kim Cc: Peter Zijlstra Cc: Sedat Dilek Cc: Song Liu Cc: Suzuki Poulouse Cc: Thomas Gleixner Cc: coresight@lists.linaro.org Cc: x86@kernel.org Link: http://lore.kernel.org/lkml/20210809111407.596077-7-leo.yan@linaro.org Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/util/auxtrace.h | 19 ------------------- 1 file changed, 19 deletions(-) diff --git a/tools/perf/util/auxtrace.h b/tools/perf/util/auxtrace.h index 79227b8..4f917636 100644 --- a/tools/perf/util/auxtrace.h +++ b/tools/perf/util/auxtrace.h @@ -440,12 +440,6 @@ struct auxtrace_cache; #ifdef HAVE_AUXTRACE_SUPPORT -/* - * In snapshot mode the mmapped page is read-only which makes using - * __sync_val_compare_and_swap() problematic. However, snapshot mode expects - * the buffer is not updated while the snapshot is made (e.g. Intel PT disables - * the event) so there is not a race anyway. - */ static inline u64 auxtrace_mmap__read_snapshot_head(struct auxtrace_mmap *mm) { struct perf_event_mmap_page *pc = mm->userpg; @@ -459,11 +453,7 @@ static inline u64 auxtrace_mmap__read_snapshot_head(struct auxtrace_mmap *mm) static inline u64 auxtrace_mmap__read_head(struct auxtrace_mmap *mm) { struct perf_event_mmap_page *pc = mm->userpg; -#if BITS_PER_LONG == 64 || !defined(HAVE_SYNC_COMPARE_AND_SWAP_SUPPORT) u64 head = READ_ONCE(pc->aux_head); -#else - u64 head = __sync_val_compare_and_swap(&pc->aux_head, 0, 0); -#endif /* Ensure all reads are done after we read the head */ smp_rmb(); @@ -473,19 +463,10 @@ static inline u64 auxtrace_mmap__read_head(struct auxtrace_mmap *mm) static inline void auxtrace_mmap__write_tail(struct auxtrace_mmap *mm, u64 tail) { struct perf_event_mmap_page *pc = mm->userpg; -#if BITS_PER_LONG != 64 && defined(HAVE_SYNC_COMPARE_AND_SWAP_SUPPORT) - u64 old_tail; -#endif /* Ensure all reads are done before we write the tail out */ smp_mb(); -#if BITS_PER_LONG == 64 || !defined(HAVE_SYNC_COMPARE_AND_SWAP_SUPPORT) WRITE_ONCE(pc->aux_tail, tail); -#else - do { - old_tail = __sync_val_compare_and_swap(&pc->aux_tail, 0, 0); - } while (!__sync_bool_compare_and_swap(&pc->aux_tail, old_tail, tail)); -#endif } int auxtrace_mmap__mmap(struct auxtrace_mmap *mm, -- 2.7.4