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Message-ID: <CAM9d7cgVHHAA0ZHaTYNx9Lmw0+hJJu_EfQRnX8K3AtLCVMznOw@mail.gmail.com>
Date: Tue, 9 Jan 2024 13:28:00 -0800
From: Namhyung Kim <namhyung@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>
Cc: Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
Stephane Eranian <eranian@...gle.com>, stable@...r.kernel.org,
"Liang, Kan" <kan.liang@...ux.intel.com>
Subject: Re: [PATCH] perf/x86: Fix out of range data
Hello,
On Sat, Dec 16, 2023 at 4:42 AM Liang, Kan <kan.liang@...ux.intel.com> 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@...ux.intel.com>
Thanks for your review, Kan.
Ingo, Peter, can you please pick this up?
Thanks,
Namhyung
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