Messages in this thread |  | | Date | Tue, 14 Mar 2023 22:41:45 +0000 | From | Ryan Roberts <> | Subject | [BUG] v6.3-rc2 regresses sched_getaffinity() for arm64 |
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Hi Linus,
I need to report a regression in v6.3-rc2 where sched_getaffinity() returns an incorrect cpu_set, at least when running on arm64. Git bisect shows this patch as the culprit, authored by you:
596ff4a09b89 cpumask: re-introduce constant-sized cpumask optimizations
Apologies if this is the wrong channel for reporting this - I couldn't find a suitable mail on the list for this patch to reply to. Happy to direct it somewhere else if appropriate.
Details:
I'm running v6.3-rc2 kernel in a VM on Ampere Altra (arm64 system). The VM is assigned 8 vCPUs. The kernel is defconfig and I'm booting into an Ubuntu user-space. `nproc` returns a value that fluctuates from call to call in the range ~80-100. If I run with v6.2, nproc always returns 8, as expected.
nproc is calling sched_getaffinity() with a 1024 entry cpu_set mask, then adds up all the set bits to find the number of CPUs. I wrote a test program and can see that the first 8 bits are always correctly set and most of the other bits are always correctly 0. But bits ~64-224 are randomly set/clear from call to call.
Test program:
#define _GNU_SOURCE /* See feature_test_macros(7) */ #include <sched.h> #include <stdio.h>
#define SET_SIZE 1024
static void print_cpu_set(cpu_set_t *cpu_set) { int ret, i, j, k;
printf("cpu_count=%d\n", CPU_COUNT(cpu_set)); for (i = 0; i < SET_SIZE;) { printf("[%03d]: ", i); for (k = 0; k < 8; k++) { for (j = 0; j < 8; j++, i++) { printf("%d", CPU_ISSET(i, cpu_set)); } printf(" "); } printf("\n"); } }
int main() { int ret; cpu_set_t *cpu_set; size_t size;
cpu_set = CPU_ALLOC(SET_SIZE); size = CPU_ALLOC_SIZE(SET_SIZE); CPU_ZERO(cpu_set);
printf("before:\n"); print_cpu_set(cpu_set); ret = sched_getaffinity(0, size, cpu_set); printf("ret=%d\n", ret); printf("after:\n"); print_cpu_set(cpu_set);
return 0; }
Broken output on v6.3-rc2:
before: cpu_count=0 [000]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [064]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [128]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [192]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [256]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [320]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [384]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [448]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [512]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [576]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [640]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [704]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [768]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [832]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [896]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [960]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 ret=0 after: cpu_count=82 [000]: 11111111 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [064]: 00000100 10110111 00110010 01101001 11111111 11111111 00000000 00000000 [128]: 00010101 00001101 11011111 10001110 11110001 10100101 11111111 11111111 [192]: 00000000 00001000 00000000 00000100 00000000 00000000 00000000 00000000 [256]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [320]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [384]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [448]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [512]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [576]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [640]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [704]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [768]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [832]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [896]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [960]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
Correct output in v6.2:
before: cpu_count=0 [000]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [064]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [128]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [192]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [256]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [320]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [384]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [448]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [512]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [576]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [640]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [704]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [768]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [832]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [896]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [960]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 ret=0 after: cpu_count=8 [000]: 11111111 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [064]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [128]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [192]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [256]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [320]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [384]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [448]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [512]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [576]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [640]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [704]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [768]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [832]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [896]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [960]: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
Thanks, Ryan
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