linux-kernel - [tip:timers/urgent] timekeeping/vsyscall: Use __iter_div_u64

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Date:   Wed, 10 Jul 2019 11:43:15 -0700
From:   tip-bot for Arnd Bergmann <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, arnd@...db.de, hpa@...or.com,
        natechancellor@...il.com, tglx@...utronix.de, mingo@...nel.org
Subject: [tip:timers/urgent] timekeeping/vsyscall: Use __iter_div_u64_rem()

Commit-ID:  0df1c9868c3a1916198ee09c323ca5932a0b8a11
Gitweb:     https://git.kernel.org/tip/0df1c9868c3a1916198ee09c323ca5932a0b8a11
Author:     Arnd Bergmann <arnd@...db.de>
AuthorDate: Wed, 10 Jul 2019 15:01:53 +0200
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Wed, 10 Jul 2019 20:37:49 +0200

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@...db.de>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Nathan Chancellor <natechancellor@...il.com>
Tested-by: Nathan Chancellor <natechancellor@...il.com>
Link: https://lkml.kernel.org/r/20190710130206.1670830-1-arnd@arndb.de
---
 kernel/time/vsyscall.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/kernel/time/vsyscall.c b/kernel/time/vsyscall.c
index a80893180826..8cf3596a4ce6 100644
--- 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);