The following commit has been merged into the perf/urgent branch of tip:

Commit-ID: dec8ced871e17eea46f097542dd074d022be4bd1 Gitweb: https://git.kernel.org/tip/dec8ced871e17eea46f097542dd074d022be4bd1 Author: Namhyung Kim namhyung@kernel.org AuthorDate: Tue, 05 Mar 2024 22:10:03 -08:00 Committer: Ingo Molnar mingo@kernel.org CommitterDate: Wed, 10 Apr 2024 06:12:01 +02:00

perf/x86: Fix out of range data

On x86 each struct cpu_hw_events maintains a table for counter assignment but it missed to update one for the deleted event in x86_pmu_del(). This can make perf_clear_dirty_counters() reset used counter if it's called before event scheduling or enabling. Then it would return out of range data which doesn't make sense.

The following code can reproduce the problem.

$ cat repro.c #include <pthread.h> #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <linux/perf_event.h> #include <sys/ioctl.h> #include <sys/mman.h> #include <sys/syscall.h>

struct perf_event_attr attr = { .type = PERF_TYPE_HARDWARE, .config = PERF_COUNT_HW_CPU_CYCLES, .disabled = 1, };

void *worker(void *arg) { int cpu = (long)arg; int fd1 = syscall(SYS_perf_event_open, &attr, -1, cpu, -1, 0); int fd2 = syscall(SYS_perf_event_open, &attr, -1, cpu, -1, 0); void *p;

do { ioctl(fd1, PERF_EVENT_IOC_ENABLE, 0); p = mmap(NULL, 4096, PROT_READ, MAP_SHARED, fd1, 0); ioctl(fd2, PERF_EVENT_IOC_ENABLE, 0);

ioctl(fd2, PERF_EVENT_IOC_DISABLE, 0); munmap(p, 4096); ioctl(fd1, PERF_EVENT_IOC_DISABLE, 0); } while (1);

return NULL; }

int main(void) { int i; int n = sysconf(_SC_NPROCESSORS_ONLN); pthread_t *th = calloc(n, sizeof(*th));

for (i = 0; i < n; i++) pthread_create(&th[i], NULL, worker, (void *)(long)i); for (i = 0; i < n; i++) pthread_join(th[i], NULL);

free(th); return 0; }

And you can see the out of range data using perf stat like this. Probably it'd be easier to see on a large machine.

$ gcc -o repro repro.c -pthread $ ./repro & $ sudo perf stat -A -I 1000 2>&1 | awk '{ if (length($3) > 15) print }' 1.001028462 CPU6 196,719,295,683,763 cycles # 194290.996 GHz (71.54%) 1.001028462 CPU3 396,077,485,787,730 branch-misses # 15804359784.80% of all branches (71.07%) 1.001028462 CPU17 197,608,350,727,877 branch-misses # 14594186554.56% of all branches (71.22%) 2.020064073 CPU4 198,372,472,612,140 cycles # 194681.113 GHz (70.95%) 2.020064073 CPU6 199,419,277,896,696 cycles # 195720.007 GHz (70.57%) 2.020064073 CPU20 198,147,174,025,639 cycles # 194474.654 GHz (71.03%) 2.020064073 CPU20 198,421,240,580,145 stalled-cycles-frontend # 100.14% frontend cycles idle (70.93%) 3.037443155 CPU4 197,382,689,923,416 cycles # 194043.065 GHz (71.30%) 3.037443155 CPU20 196,324,797,879,414 cycles # 193003.773 GHz (71.69%) 3.037443155 CPU5 197,679,956,608,205 stalled-cycles-backend # 1315606428.66% backend cycles idle (71.19%) 3.037443155 CPU5 198,571,860,474,851 instructions # 13215422.58 insn per cycle

It should move the contents in the cpuc->assign as well.

Fixes: 5471eea5d3bf ("perf/x86: Reset the dirty counter to prevent the leak for an RDPMC task") Signed-off-by: Namhyung Kim namhyung@kernel.org Signed-off-by: Ingo Molnar mingo@kernel.org Reviewed-by: Kan Liang kan.liang@linux.intel.com Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20240306061003.1894224-1-namhyung@kernel.org --- arch/x86/events/core.c | 1 + 1 file changed, 1 insertion(+)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c index 0905064..5b0dd07 100644 --- a/arch/x86/events/core.c +++ b/arch/x86/events/core.c @@ -1644,6 +1644,7 @@ static void x86_pmu_del(struct perf_event *event, int flags) while (++i < cpuc->n_events) { cpuc->event_list[i-1] = cpuc->event_list[i]; cpuc->event_constraint[i-1] = cpuc->event_constraint[i]; + cpuc->assign[i-1] = cpuc->assign[i]; } cpuc->event_constraint[i-1] = NULL; --cpuc->n_events;