Ping!
On Tue, Jan 9, 2024 at 1:28 PM Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
>
> Hello,
>
> On Sat, Dec 16, 2023 at 4:42 AM Liang, Kan <kan.liang@xxxxxxxxxxxxxxx> wrote:
> >
> >
> >
> > On 2023-12-16 2:28 a.m., Namhyung Kim wrote:
> > > On x86 each 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.
> >
> > Yes, the patch looks good to me.
> >
> > Reviewed-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
>
> Thanks for your review, Kan.
>
> Ingo, Peter, can you please pick this up?
>
> Thanks,
> Namhyung
