kernel/tools/perf/util/cloexec.c

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