From 995a46bbfba9964e328e3947130919d8bd3cd62a Mon Sep 17 00:00:00 2001 From: Meador Inge Date: Fri, 13 Jun 2014 14:02:04 +0530 Subject: [PATCH] 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 #include #include 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. --- ChangeLog | 6 ++++++ NEWS | 2 +- sysdeps/unix/sysv/linux/getsysstats.c | 4 ++-- 3 files changed, 9 insertions(+), 3 deletions(-) diff --git a/ChangeLog b/ChangeLog index 83764a5..d5474af 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,9 @@ +2014-06-13 Meador Inge + + [BZ #16996] + sysdeps/unix/sysv/linux/getsysstats.c (__get_nprocs): Ensure + that the cached result has been set before returning it. + 2014-06-12 Roland McGrath * nptl/sysdeps/unix/sysv/linux/sparc/bits/pthreadtypes.h: Moved ... diff --git a/NEWS b/NEWS index 655226d..38cc5b5 100644 --- a/NEWS +++ b/NEWS @@ -19,7 +19,7 @@ Version 2.20 16791, 16796, 16799, 16800, 16815, 16823, 16824, 16831, 16838, 16849, 16854, 16876, 16877, 16878, 16882, 16885, 16888, 16890, 16912, 16915, 16916, 16917, 16922, 16927, 16928, 16932, 16943, 16958, 16965, 16966, - 16967, 16977, 16978, 16984, 16990, 17009, 17042, 17048. + 16967, 16977, 16978, 16984, 16990, 16996, 17009, 17042, 17048. * The minimum Linux kernel version that this version of the GNU C Library can be used with is 2.6.32. diff --git a/sysdeps/unix/sysv/linux/getsysstats.c b/sysdeps/unix/sysv/linux/getsysstats.c index b6a6fe3..755c259 100644 --- a/sysdeps/unix/sysv/linux/getsysstats.c +++ b/sysdeps/unix/sysv/linux/getsysstats.c @@ -126,13 +126,13 @@ next_line (int fd, char *const buffer, char **cp, char **re, int __get_nprocs (void) { - static int cached_result; + static int cached_result = -1; static time_t timestamp; time_t now = time (NULL); time_t prev = timestamp; atomic_read_barrier (); - if (now == prev) + if (now == prev && cached_result > -1) return cached_result; /* XXX Here will come a test for the new system call. */ -- 2.7.4