Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756653Ab0GGVTT (ORCPT ); Wed, 7 Jul 2010 17:19:19 -0400 Received: from e5.ny.us.ibm.com ([32.97.182.145]:48478 "EHLO e5.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756272Ab0GGVTS (ORCPT ); Wed, 7 Jul 2010 17:19:18 -0400 From: John Stultz To: linux-kernel@vger.kernel.org Cc: John Stultz , Jiri Olsa , Thomas Gleixner , Oleg Nesterov Subject: [PATCH] x86: Fix vtime/file timestamp inconsistencies Date: Wed, 7 Jul 2010 14:19:14 -0700 Message-Id: <1278537554-12013-1-git-send-email-johnstul@us.ibm.com> X-Mailer: git-send-email 1.6.0.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2107 Lines: 72 Due to vtime calling vgettimeofday(), its possible that an application could call time();create("stuff",O_RDRW); only to see the file's creation timestamp to be before the value returned by time. A similar way to reproduce the issue is to compare the vsyscall time() with the syscall time(), and observe ordering issues. The modified test case from Oleg Nesterov below can illustrate this: int main(void) { time_t sec1,sec2; do { sec1 = time(&sec2); sec2 = syscall(__NR_time, NULL); } while (sec1 <= sec2); printf("vtime: %d.000000\n", sec1); printf("time: %d.000000\n", sec2); return 0; } The proper fix is to make vtime use the same time value as current_kernel_time() (which is exported via update_vsyscall) instead of vgettime(). Thanks to Jiri Olsa for bringing up the issue and catching bugs in earlier verisons of this fix. Signed-off-by: John Stultz CC: Jiri Olsa CC: Thomas Gleixner CC: Oleg Nesterov --- arch/x86/kernel/vsyscall_64.c | 11 ++++++++--- 1 files changed, 8 insertions(+), 3 deletions(-) diff --git a/arch/x86/kernel/vsyscall_64.c b/arch/x86/kernel/vsyscall_64.c index 1c0c6ab..dce0c3c 100644 --- a/arch/x86/kernel/vsyscall_64.c +++ b/arch/x86/kernel/vsyscall_64.c @@ -169,13 +169,18 @@ int __vsyscall(0) vgettimeofday(struct timeval * tv, struct timezone * tz) * unlikely */ time_t __vsyscall(1) vtime(time_t *t) { - struct timeval tv; + unsigned seq; time_t result; if (unlikely(!__vsyscall_gtod_data.sysctl_enabled)) return time_syscall(t); - vgettimeofday(&tv, NULL); - result = tv.tv_sec; + do { + seq = read_seqbegin(&__vsyscall_gtod_data.lock); + + result = __vsyscall_gtod_data.wall_time_sec; + + } while (read_seqretry(&__vsyscall_gtod_data.lock, seq)); + if (t) *t = result; return result; -- 1.6.0.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/