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 <asm/unistd.h>
  11 #include <sys/syscall.h>
  12
  13 static unsigned long flag = PERF_FLAG_FD_CLOEXEC;
  14
  15 int __weak sched_getcpu(void)
  16 {
  17 #ifdef __NR_getcpu
  18         unsigned cpu;
  19         int err = syscall(__NR_getcpu, &cpu, NULL, NULL);
  20         if (!err)
  21                 return cpu;
  22 #else
  23         errno = ENOSYS;
  24 #endif
  25         return -1;
  26 }
  27
  28 static int perf_flag_probe(void)
  29 {
  30         /* use 'safest' configuration as used in perf_evsel__fallback() */
  31         struct perf_event_attr attr = {
  32                 .type = PERF_TYPE_SOFTWARE,
  33                 .config = PERF_COUNT_SW_CPU_CLOCK,
  34                 .exclude_kernel = 1,
  35         };
  36         int fd;
  37         int err;
  38         int cpu;
  39         pid_t pid = -1;
  40         char sbuf[STRERR_BUFSIZE];
  41
  42         cpu = sched_getcpu();
  43         if (cpu < 0)
  44                 cpu = 0;
  45
  46         /*
  47          * Using -1 for the pid is a workaround to avoid gratuitous jump label
  48          * changes.
  49          */
  50         while (1) {
  51                 /* check cloexec flag */
  52                 fd = sys_perf_event_open(&attr, pid, cpu, -1,
  53                                          PERF_FLAG_FD_CLOEXEC);
  54                 if (fd < 0 && pid == -1 && errno == EACCES) {
  55                         pid = 0;
  56                         continue;
  57                 }
  58                 break;
  59         }
  60         err = errno;
  61
  62         if (fd >= 0) {
  63                 close(fd);
  64                 return 1;
  65         }
  66
  67         WARN_ONCE(err != EINVAL && err != EBUSY,
  68                   "perf_event_open(..., PERF_FLAG_FD_CLOEXEC) failed with unexpected error %d (%s)\n",
  69                   err, str_error_r(err, sbuf, sizeof(sbuf)));
  70
  71         /* not supported, confirm error related to PERF_FLAG_FD_CLOEXEC */
  72         while (1) {
  73                 fd = sys_perf_event_open(&attr, pid, cpu, -1, 0);
  74                 if (fd < 0 && pid == -1 && errno == EACCES) {
  75                         pid = 0;
  76                         continue;
  77                 }
  78                 break;
  79         }
  80         err = errno;
  81
  82         if (fd >= 0)
  83                 close(fd);
  84
  85         if (WARN_ONCE(fd < 0 && err != EBUSY,
  86                       "perf_event_open(..., 0) failed unexpectedly with error %d (%s)\n",
  87                       err, str_error_r(err, sbuf, sizeof(sbuf))))
  88                 return -1;
  89
  90         return 0;
  91 }
  92
  93 unsigned long perf_event_open_cloexec_flag(void)
  94 {
  95         static bool probed;
  96
  97         if (!probed) {
  98                 if (perf_flag_probe() <= 0)
  99                         flag = 0;
 100                 probed = true;
 101         }
 102
 103         return flag;
 104 }