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authorMeador Inge <meadori@codesourcery.com>2014-06-13 14:02:04 +0530
committerSiddhesh Poyarekar <siddhesh@redhat.com>2014-06-13 14:02:04 +0530
commit995a46bbfba9964e328e3947130919d8bd3cd62a (patch)
treec36f1da1cc528a8cfc1d891310be2599c0507532 /nptl
parentfebf6cc58c36cd5a978b8b5faedb5a932eb44c98 (diff)
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get_nprocs: Only return explictly set cache values (BZ #16996)
The implementation of __get_nprocs uses a stactic variable to cache
the value of the current number of processors.  The caching breaks when
'time (NULL) == 0':

  $ cat nproc.c
  #include <stdio.h>
  #include <time.h>
  #include <sys/time.h>

  int main(int argc, char *argv[])
  {
    time_t t;
    struct timeval tv = {0, 0};
    printf("settimeofday({0, 0}, NULL) = %d\n", settimeofday(&tv, NULL));
    t = time(NULL);
    printf("Time: %d, CPUs: %d\n", (unsigned int)t, get_nprocs());
    return 0;
  }
  $ gcc -O3 nproc.c
  $ ./a.out
  settimeofday({0, 0}, NULL) = -1
  Time: 1401311578, CPUs: 4
  $ sudo ./a.out
  settimeofday({0, 0}, NULL) = 0
  Time: 0, CPUs: 0

The problem is with the condition used to check whether a cached
value should be returned or not:

  static int cached_result;
  static time_t timestamp;

  time_t now = time (NULL);
  time_t prev = timestamp;
  atomic_read_barrier ();
  if (now == prev)
    return cached_result;

This patch fixes the problem by ensuring that 'cached_result' has
been set at least once before returning it.
Diffstat (limited to 'nptl')
0 files changed, 0 insertions, 0 deletions