[RT] fix delay in do_vgettimeofday() in arch/x86_64/kernel/vsyscall.c

[Serge Belyshev <belyshev@depni.sinp.msu.ru>]

There are occasional very very long (30..60 sec) delays happening when calling
gettimeofday() vsyscall on x86_64 with 2.6.14-rt22 kernel.

These delays come from while() looping over invalid data that are
going to be discarded by seqlock.



 arch/x86_64/kernel/vsyscall.c |   15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

Index: linux/arch/x86_64/kernel/vsyscall.c
===================================================================
--- linux.orig/arch/x86_64/kernel/vsyscall.c
+++ linux/arch/x86_64/kernel/vsyscall.c
@@ -111,14 +111,15 @@ static force_inline void do_vgettimeofda
 
 		/* add nsec offset to wall_time_tv */
 		*tv = __vsyscall_gtod_data.wall_time_tv;
-		do_div(nsec_delta, NSEC_PER_USEC);
-		tv->tv_usec += (unsigned long) nsec_delta;
-
-		while (tv->tv_usec > USEC_PER_SEC) {
-			tv->tv_sec += 1;
-			tv->tv_usec -= USEC_PER_SEC;
-		}
 	} while (read_seqretry(&__vsyscall_gtod_lock, seq));
+
+	do_div(nsec_delta, NSEC_PER_USEC);
+	tv->tv_usec += (unsigned long) nsec_delta;
+
+	while (tv->tv_usec > USEC_PER_SEC) {
+		tv->tv_sec += 1;
+		tv->tv_usec -= USEC_PER_SEC;
+	}
 }
 
 /*