[tip: timers/core] lib/vdso: Only read hrtimer_res when needed in __cvdso_clock_getres()

["tip-bot2 for Christophe Leroy" <tip-bot2@linutronix.de>]

The following commit has been merged into the timers/core branch of tip:

Commit-ID:     49a101d7169c7729c7bab6b2f896faae34bd6c3d
Gitweb:        https://git.kernel.org/tip/49a101d7169c7729c7bab6b2f896faae34bd6c3d
Author:        Christophe Leroy <christophe.leroy@c-s.fr>
AuthorDate:    Thu, 16 Jan 2020 17:58:27 
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Thu, 16 Jan 2020 21:24:46 +01:00

lib/vdso: Only read hrtimer_res when needed in __cvdso_clock_getres()

Only perform READ_ONCE(vd[CS_HRES_COARSE].hrtimer_res) for
HRES and RAW clocks.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/7ac2f0d21652f95e2bbdfa6bd514ae6c7caf53ab.1579196675.git.christophe.leroy@c-s.fr
---
 lib/vdso/gettimeofday.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/lib/vdso/gettimeofday.c b/lib/vdso/gettimeofday.c
index f342ac1..f8b8ec5 100644
--- a/lib/vdso/gettimeofday.c
+++ b/lib/vdso/gettimeofday.c
@@ -312,7 +312,6 @@ static __maybe_unused
 int __cvdso_clock_getres_common(clockid_t clock, struct __kernel_timespec *res)
 {
 	const struct vdso_data *vd = __arch_get_vdso_data();
-	u64 hrtimer_res;
 	u32 msk;
 	u64 ns;
 
@@ -323,7 +322,6 @@ int __cvdso_clock_getres_common(clockid_t clock, struct __kernel_timespec *res)
 	if (IS_ENABLED(CONFIG_TIME_NS) && vd->clock_mode == VCLOCK_TIMENS)
 		vd = __arch_get_timens_vdso_data();
 
-	hrtimer_res = READ_ONCE(vd[CS_HRES_COARSE].hrtimer_res);
 	/*
 	 * Convert the clockid to a bitmask and use it to check which
 	 * clocks are handled in the VDSO directly.
@@ -333,7 +331,7 @@ int __cvdso_clock_getres_common(clockid_t clock, struct __kernel_timespec *res)
 		/*
 		 * Preserves the behaviour of posix_get_hrtimer_res().
 		 */
-		ns = hrtimer_res;
+		ns = READ_ONCE(vd[CS_HRES_COARSE].hrtimer_res);
 	} else if (msk & VDSO_COARSE) {
 		/*
 		 * Preserves the behaviour of posix_get_coarse_res().