tools/perf/util/cloexec.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <errno.h>
   3 #include <sched.h>
   4 #include "util.h"
   5 #include "../perf.h"
   6 #include "cloexec.h"
   7 #include "asm/bug.h"
   8 #include "debug.h"
   9 #include <unistd.h>
  10 #include <sys/syscall.h>
  11
  12 static unsigned long flag = PERF_FLAG_FD_CLOEXEC;
  13
  14 int __weak sched_getcpu(void)
  15 {
  16 #ifdef __NR_getcpu
  17         unsigned cpu;
  18         int err = syscall(__NR_getcpu, &cpu, NULL, NULL);
  19         if (!err)
  20                 return cpu;
  21 #else
  22         errno = ENOSYS;
  23 #endif
  24         return -1;
  25 }
  26
  27 static int perf_flag_probe(void)
  28 {
  29         /* use 'safest' configuration as used in perf_evsel__fallback() */
  30         struct perf_event_attr attr = {
  31                 .type = PERF_TYPE_SOFTWARE,
  32                 .config = PERF_COUNT_SW_CPU_CLOCK,
  33                 .exclude_kernel = 1,
  34         };
  35         int fd;
  36         int err;
  37         int cpu;
  38         pid_t pid = -1;
  39         char sbuf[STRERR_BUFSIZE];
  40
  41         cpu = sched_getcpu();
  42         if (cpu < 0)
  43                 cpu = 0;
  44
  45         /*
  46          * Using -1 for the pid is a workaround to avoid gratuitous jump label
  47          * changes.
  48          */
  49         while (1) {
  50                 /* check cloexec flag */
  51                 fd = sys_perf_event_open(&attr, pid, cpu, -1,
  52                                          PERF_FLAG_FD_CLOEXEC);
  53                 if (fd < 0 && pid == -1 && errno == EACCES) {
  54                         pid = 0;
  55                         continue;
  56                 }
  57                 break;
  58         }
  59         err = errno;
  60
  61         if (fd >= 0) {
  62                 close(fd);
  63                 return 1;
  64         }
  65
  66         WARN_ONCE(err != EINVAL && err != EBUSY,
  67                   "perf_event_open(..., PERF_FLAG_FD_CLOEXEC) failed with unexpected error %d (%s)\n",
  68                   err, str_error_r(err, sbuf, sizeof(sbuf)));
  69
  70         /* not supported, confirm error related to PERF_FLAG_FD_CLOEXEC */
  71         while (1) {
  72                 fd = sys_perf_event_open(&attr, pid, cpu, -1, 0);
  73                 if (fd < 0 && pid == -1 && errno == EACCES) {
  74                         pid = 0;
  75                         continue;
  76                 }
  77                 break;
  78         }
  79         err = errno;
  80
  81         if (fd >= 0)
  82                 close(fd);
  83
  84         if (WARN_ONCE(fd < 0 && err != EBUSY,
  85                       "perf_event_open(..., 0) failed unexpectedly with error %d (%s)\n",
  86                       err, str_error_r(err, sbuf, sizeof(sbuf))))
  87                 return -1;
  88
  89         return 0;
  90 }
  91
  92 unsigned long perf_event_open_cloexec_flag(void)
  93 {
  94         static bool probed;
  95
  96         if (!probed) {
  97                 if (perf_flag_probe() <= 0)
  98                         flag = 0;
  99                 probed = true;
 100         }
 101
 102         return flag;
 103 }