[PATCH] x86_64 : fix vtime() vsyscall

[PATCH] x86_64 : fix vtime() vsyscall

[Eric Dumazet]

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There is a tiny probability that the return value from vtime(time_t *t) is 
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>

[-- Attachment #2: vtime_fix.patch --]
[-- Type: text/plain, Size: 667 bytes --]

--- linux-2.6.21-rc5-mm1/arch/x86_64/kernel/vsyscall.c
+++ linux-2.6.21-rc5-mm1-ed/arch/x86_64/kernel/vsyscall.c
@@ -147,15 +147,15 @@ int __vsyscall(0) vgettimeofday(struct t
 	return 0;
 }
 
-/* This will break when the xtime seconds get inaccurate, but that is
- * unlikely */
 time_t __vsyscall(1) vtime(time_t *t)
 {
+	time_t result;
 	if (!__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.