[PATCH] x86-64: fix vtime() vsyscall

There is a tiny probability that the return value from vtime(time_t *t) is
Signed-off-by: Andi Kleen <ak@suse.de>
different than the value stored in *t

Using a temporary variable solves the problem and gives a faster code.

   17:   48 85 ff                test   %rdi,%rdi
   1a:   48 8b 05 00 00 00 00    mov    0(%rip),%rax        #
__vsyscall_gtod_data.wall_time_tv.tv_sec
   21:   74 03                   je     26
   23:   48 89 07                mov    %rax,(%rdi)
   26:   c9                      leaveq
   27:   c3                      retq

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>

diff --git a/arch/x86_64/kernel/vsyscall.c b/arch/x86_64/kernel/vsyscall.c
index d14cbb3e0ebed074aa35f8591dd656aacb46428c..ba330f87067996a17495f7d03466d646c718b52c 100644 (file)
--- a/arch/x86_64/kernel/vsyscall.c
+++ b/arch/x86_64/kernel/vsyscall.c
@@ -156,11 +156,13 @@ int __vsyscall(0) vgettimeofday(struct timeval * tv, struct timezone * tz)
  * unlikely */
 time_t __vsyscall(1) vtime(time_t *t)
 {
+       time_t result;
        if (unlikely(!__vsyscall_gtod_data.sysctl_enabled))
                return time_syscall(t);
-       else if (t)
-               *t = __vsyscall_gtod_data.wall_time_tv.tv_sec;
-       return __vsyscall_gtod_data.wall_time_tv.tv_sec;
+       result = __vsyscall_gtod_data.wall_time_tv.tv_sec;
+       if (t)
+               *t = result;
+       return result;
 }
 
 /* Fast way to get current CPU and node.