Hi Mark, I love your patch! Perhaps something to improve:
[auto build test WARNING on tip/perf/core] [also build test WARNING on v4.17-rc4 next-20180510] [if your patch is applied to the wrong git tree, please drop us a note to help improve the system] url: https://github.com/0day-ci/linux/commits/Mark-Rutland/perf-ring_buffer-ensure-atomicity-and-order-of-updates/20180511-070205 config: i386-randconfig-s1-201818 (attached as .config) compiler: gcc-6 (Debian 6.4.0-9) 6.4.0 20171026 reproduce: # save the attached .config to linux build tree make ARCH=i386 All warnings (new ones prefixed by >>): In file included from include/uapi/linux/swab.h:6:0, from include/linux/swab.h:5, from include/uapi/linux/byteorder/little_endian.h:13, from include/linux/byteorder/little_endian.h:5, from arch/x86/include/uapi/asm/byteorder.h:5, from include/uapi/linux/perf_event.h:20, from include/linux/perf_event.h:17, from kernel//events/ring_buffer.c:12: kernel//events/ring_buffer.c: In function 'perf_output_put_handle': include/linux/compiler.h:339:38: error: call to '__compiletime_assert_86' declared with attribute error: Need native word sized stores/loads for atomicity. _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__) ^ include/linux/compiler.h:319:4: note: in definition of macro '__compiletime_assert' prefix ## suffix(); \ ^~~~~~ include/linux/compiler.h:339:2: note: in expansion of macro '_compiletime_assert' _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__) ^~~~~~~~~~~~~~~~~~~ >> include/linux/compiler.h:342:2: note: in expansion of macro >> 'compiletime_assert' compiletime_assert(__native_word(t), \ ^~~~~~~~~~~~~~~~~~ >> include/asm-generic/barrier.h:181:2: note: in expansion of macro >> 'compiletime_assert_atomic_type' compiletime_assert_atomic_type(*p); \ ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ >> kernel//events/ring_buffer.c:86:2: note: in expansion of macro >> 'smp_store_release' smp_store_release(&rb->user_page->data_head, head); /* B, matches C */ ^~~~~~~~~~~~~~~~~ kernel//events/ring_buffer.c: In function 'perf_aux_output_skip': include/linux/compiler.h:339:38: error: call to '__compiletime_assert_498' declared with attribute error: Need native word sized stores/loads for atomicity. _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__) ^ include/linux/compiler.h:319:4: note: in definition of macro '__compiletime_assert' prefix ## suffix(); \ ^~~~~~ include/linux/compiler.h:339:2: note: in expansion of macro '_compiletime_assert' _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__) ^~~~~~~~~~~~~~~~~~~ >> include/linux/compiler.h:342:2: note: in expansion of macro >> 'compiletime_assert' compiletime_assert(__native_word(t), \ ^~~~~~~~~~~~~~~~~~ >> include/asm-generic/barrier.h:181:2: note: in expansion of macro >> 'compiletime_assert_atomic_type' compiletime_assert_atomic_type(*p); \ ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ kernel//events/ring_buffer.c:498:2: note: in expansion of macro 'smp_store_release' smp_store_release(&rb->user_page->aux_head, rb->aux_head); ^~~~~~~~~~~~~~~~~ kernel//events/ring_buffer.c: In function 'perf_aux_output_end': include/linux/compiler.h:339:38: error: call to '__compiletime_assert_466' declared with attribute error: Need native word sized stores/loads for atomicity. _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__) ^ include/linux/compiler.h:319:4: note: in definition of macro '__compiletime_assert' prefix ## suffix(); \ ^~~~~~ include/linux/compiler.h:339:2: note: in expansion of macro '_compiletime_assert' _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__) ^~~~~~~~~~~~~~~~~~~ >> include/linux/compiler.h:342:2: note: in expansion of macro >> 'compiletime_assert' compiletime_assert(__native_word(t), \ ^~~~~~~~~~~~~~~~~~ >> include/asm-generic/barrier.h:181:2: note: in expansion of macro >> 'compiletime_assert_atomic_type' compiletime_assert_atomic_type(*p); \ ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ kernel//events/ring_buffer.c:466:2: note: in expansion of macro 'smp_store_release' smp_store_release(&rb->user_page->aux_head, rb->aux_head); ^~~~~~~~~~~~~~~~~ -- In file included from include/uapi/linux/swab.h:6:0, from include/linux/swab.h:5, from include/uapi/linux/byteorder/little_endian.h:13, from include/linux/byteorder/little_endian.h:5, from arch/x86/include/uapi/asm/byteorder.h:5, from include/uapi/linux/perf_event.h:20, from include/linux/perf_event.h:17, from kernel/events/ring_buffer.c:12: kernel/events/ring_buffer.c: In function 'perf_output_put_handle': include/linux/compiler.h:339:38: error: call to '__compiletime_assert_86' declared with attribute error: Need native word sized stores/loads for atomicity. _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__) ^ include/linux/compiler.h:319:4: note: in definition of macro '__compiletime_assert' prefix ## suffix(); \ ^~~~~~ include/linux/compiler.h:339:2: note: in expansion of macro '_compiletime_assert' _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__) ^~~~~~~~~~~~~~~~~~~ >> include/linux/compiler.h:342:2: note: in expansion of macro >> 'compiletime_assert' compiletime_assert(__native_word(t), \ ^~~~~~~~~~~~~~~~~~ >> include/asm-generic/barrier.h:181:2: note: in expansion of macro >> 'compiletime_assert_atomic_type' compiletime_assert_atomic_type(*p); \ ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ kernel/events/ring_buffer.c:86:2: note: in expansion of macro 'smp_store_release' smp_store_release(&rb->user_page->data_head, head); /* B, matches C */ ^~~~~~~~~~~~~~~~~ kernel/events/ring_buffer.c: In function 'perf_aux_output_skip': include/linux/compiler.h:339:38: error: call to '__compiletime_assert_498' declared with attribute error: Need native word sized stores/loads for atomicity. _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__) ^ include/linux/compiler.h:319:4: note: in definition of macro '__compiletime_assert' prefix ## suffix(); \ ^~~~~~ include/linux/compiler.h:339:2: note: in expansion of macro '_compiletime_assert' _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__) ^~~~~~~~~~~~~~~~~~~ >> include/linux/compiler.h:342:2: note: in expansion of macro >> 'compiletime_assert' compiletime_assert(__native_word(t), \ ^~~~~~~~~~~~~~~~~~ >> include/asm-generic/barrier.h:181:2: note: in expansion of macro >> 'compiletime_assert_atomic_type' compiletime_assert_atomic_type(*p); \ ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ kernel/events/ring_buffer.c:498:2: note: in expansion of macro 'smp_store_release' smp_store_release(&rb->user_page->aux_head, rb->aux_head); ^~~~~~~~~~~~~~~~~ kernel/events/ring_buffer.c: In function 'perf_aux_output_end': include/linux/compiler.h:339:38: error: call to '__compiletime_assert_466' declared with attribute error: Need native word sized stores/loads for atomicity. _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__) ^ include/linux/compiler.h:319:4: note: in definition of macro '__compiletime_assert' prefix ## suffix(); \ ^~~~~~ include/linux/compiler.h:339:2: note: in expansion of macro '_compiletime_assert' _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__) ^~~~~~~~~~~~~~~~~~~ >> include/linux/compiler.h:342:2: note: in expansion of macro >> 'compiletime_assert' compiletime_assert(__native_word(t), \ ^~~~~~~~~~~~~~~~~~ >> include/asm-generic/barrier.h:181:2: note: in expansion of macro >> 'compiletime_assert_atomic_type' compiletime_assert_atomic_type(*p); \ ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ kernel/events/ring_buffer.c:466:2: note: in expansion of macro 'smp_store_release' smp_store_release(&rb->user_page->aux_head, rb->aux_head); ^~~~~~~~~~~~~~~~~ vim +/smp_store_release +86 kernel//events/ring_buffer.c 44 45 static void perf_output_put_handle(struct perf_output_handle *handle) 46 { 47 struct ring_buffer *rb = handle->rb; 48 unsigned long head; 49 50 again: 51 head = local_read(&rb->head); 52 53 /* 54 * IRQ/NMI can happen here, which means we can miss a head update. 55 */ 56 57 if (!local_dec_and_test(&rb->nest)) 58 goto out; 59 60 /* 61 * Since the mmap() consumer (userspace) can run on a different CPU: 62 * 63 * kernel user 64 * 65 * if (LOAD ->data_tail) { LOAD ->data_head 66 * (A) smp_rmb() (C) 67 * STORE $data LOAD $data 68 * smp_mb() (D) 69 * RELEASE ->data_head (B) STORE ->data_tail 70 * } 71 * 72 * Where A pairs with D, and B pairs with C. 73 * 74 * In our case (A) is a control dependency that separates the load of 75 * the ->data_tail and the stores of $data. In case ->data_tail 76 * indicates there is no room in the buffer to store $data we do not. 77 * 78 * D needs to be a full barrier since it separates the data READ 79 * from the tail WRITE. 80 * 81 * For B a WMB is sufficient since it separates two WRITEs, and for C 82 * an RMB is sufficient since it separates two READs. 83 * 84 * See perf_output_begin(). 85 */ > 86 smp_store_release(&rb->user_page->data_head, head); /* B, matches C */ 87 88 /* 89 * Now check if we missed an update -- rely on previous implied 90 * compiler barriers to force a re-read. 91 */ 92 if (unlikely(head != local_read(&rb->head))) { 93 local_inc(&rb->nest); 94 goto again; 95 } 96 97 if (handle->wakeup != local_read(&rb->wakeup)) 98 perf_output_wakeup(handle); 99 100 out: 101 preempt_enable(); 102 } 103 --- 0-DAY kernel test infrastructure Open Source Technology Center https://lists.01.org/pipermail/kbuild-all Intel Corporation
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