Re: [PATCH] perf/x86: Fix out of range data

[Namhyung Kim]

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