tools/perf/util/cloexec.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <errno.h>
   3 #include <sched.h>
   4 #include "util.h" // for sched_getcpu()
   5 #include "../perf-sys.h"
   6 #include "cloexec.h"
   7 #include "event.h"
   8 #include "asm/bug.h"
   9 #include "debug.h"
  10 #include <unistd.h>
  11 #include <sys/syscall.h>
  12 #include <linux/string.h>
  13
  14 static unsigned long flag = PERF_FLAG_FD_CLOEXEC;
  15
  16 static int perf_flag_probe(void)
  17 {
  18         /* use 'safest' configuration as used in evsel__fallback() */
  19         struct perf_event_attr attr = {
  20                 .type = PERF_TYPE_SOFTWARE,
  21                 .config = PERF_COUNT_SW_CPU_CLOCK,
  22                 .exclude_kernel = 1,
  23         };
  24         int fd;
  25         int err;
  26         int cpu;
  27         pid_t pid = -1;
  28         char sbuf[STRERR_BUFSIZE];
  29
  30         cpu = sched_getcpu();
  31         if (cpu < 0)
  32                 cpu = 0;
  33
  34         /*
  35          * Using -1 for the pid is a workaround to avoid gratuitous jump label
  36          * changes.
  37          */
  38         while (1) {
  39                 /* check cloexec flag */
  40                 fd = sys_perf_event_open(&attr, pid, cpu, -1,
  41                                          PERF_FLAG_FD_CLOEXEC);
  42                 if (fd < 0 && pid == -1 && errno == EACCES) {
  43                         pid = 0;
  44                         continue;
  45                 }
  46                 break;
  47         }
  48         err = errno;
  49
  50         if (fd >= 0) {
  51                 close(fd);
  52                 return 1;
  53         }
  54
  55         WARN_ONCE(err != EINVAL && err != EBUSY && err != EACCES,
  56                   "perf_event_open(..., PERF_FLAG_FD_CLOEXEC) failed with unexpected error %d (%s)\n",
  57                   err, str_error_r(err, sbuf, sizeof(sbuf)));
  58
  59         /* not supported, confirm error related to PERF_FLAG_FD_CLOEXEC */
  60         while (1) {
  61                 fd = sys_perf_event_open(&attr, pid, cpu, -1, 0);
  62                 if (fd < 0 && pid == -1 && errno == EACCES) {
  63                         pid = 0;
  64                         continue;
  65                 }
  66                 break;
  67         }
  68         err = errno;
  69
  70         if (fd >= 0)
  71                 close(fd);
  72
  73         if (WARN_ONCE(fd < 0 && err != EBUSY && err != EACCES,
  74                       "perf_event_open(..., 0) failed unexpectedly with error %d (%s)\n",
  75                       err, str_error_r(err, sbuf, sizeof(sbuf))))
  76                 return -1;
  77
  78         return 0;
  79 }
  80
  81 unsigned long perf_event_open_cloexec_flag(void)
  82 {
  83         static bool probed;
  84
  85         if (!probed) {
  86                 if (perf_flag_probe() <= 0)
  87                         flag = 0;
  88                 probed = true;
  89         }
  90
  91         return flag;
  92 }