timekeeping/vsyscall: Use __iter_div_u64_rem()

On 32-bit x86 when building with clang-9, the 'division' loop gets turned
back into an inefficient division that causes a link error:

kernel/time/vsyscall.o: In function `update_vsyscall':
vsyscall.c:(.text+0xe3): undefined reference to `__udivdi3'

Use the existing __iter_div_u64_rem() function which is used to address the
same issue in other places.

Fixes: 44f57d788e7d ("timekeeping: Provide a generic update_vsyscall() implementation")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Tested-by: Nathan Chancellor <natechancellor@gmail.com>
Link: https://lkml.kernel.org/r/20190710130206.1670830-1-arnd@arndb.de

diff --git a/kernel/time/vsyscall.c b/kernel/time/vsyscall.c
index a808931808261eeeabed43c9b6df69917fbdc204..8cf3596a4ce677ca787e214d6f33b32a6d6b4088 100644 (file)
--- a/kernel/time/vsyscall.c
+++ b/kernel/time/vsyscall.c
@@ -104,11 +104,7 @@ void update_vsyscall(struct timekeeper *tk)
        vdso_ts->sec    = tk->xtime_sec + tk->wall_to_monotonic.tv_sec;
        nsec            = tk->tkr_mono.xtime_nsec >> tk->tkr_mono.shift;
        nsec            = nsec + tk->wall_to_monotonic.tv_nsec;
-       while (nsec >= NSEC_PER_SEC) {
-               nsec = nsec - NSEC_PER_SEC;
-               vdso_ts->sec++;
-       }
-       vdso_ts->nsec   = nsec;
+       vdso_ts->sec    += __iter_div_u64_rem(nsec, NSEC_PER_SEC, &vdso_ts->nsec);
 
        if (__arch_use_vsyscall(vdata))
                update_vdso_data(vdata, tk);