[PATCH 04/14] vdso/helpers: Add helpers for seqlocks of single vdso_clock

[Thomas Weißschuh]

Auxiliary clocks will have their vDSO data in a dedicated 'struct vdso_clock',
which needs to be synchronized independently.

Add a helper to synchronize a single vDSO clock.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@xxxxxxxxxxxxx>
---
 include/vdso/helpers.h | 40 +++++++++++++++++++++++++++-------------
 1 file changed, 27 insertions(+), 13 deletions(-)

diff --git a/include/vdso/helpers.h b/include/vdso/helpers.h
index 0a98fed550ba66a84a620fbbd6aee3e3029b4772..a5679f5efdfdcaaf6efd5f4a317d1f132c3dc617 100644
--- a/include/vdso/helpers.h
+++ b/include/vdso/helpers.h
@@ -28,32 +28,46 @@ static __always_inline u32 vdso_read_retry(const struct vdso_clock *vc,
 	return seq != start;
 }
 
-static __always_inline void vdso_write_begin(struct vdso_time_data *vd)
+static __always_inline void vdso_write_begin_clock(struct vdso_clock *vc, bool last)
 {
-	struct vdso_clock *vc = vd->clock_data;
-
 	/*
 	 * WRITE_ONCE() is required otherwise the compiler can validly tear
-	 * updates to vd[x].seq and it is possible that the value seen by the
+	 * updates to vc->seq and it is possible that the value seen by the
 	 * reader is inconsistent.
 	 */
-	WRITE_ONCE(vc[CS_HRES_COARSE].seq, vc[CS_HRES_COARSE].seq + 1);
-	WRITE_ONCE(vc[CS_RAW].seq, vc[CS_RAW].seq + 1);
-	smp_wmb();
+	WRITE_ONCE(vc->seq, vc->seq + 1);
+
+	if (last)
+		smp_wmb();
 }
 
-static __always_inline void vdso_write_end(struct vdso_time_data *vd)
+static __always_inline void vdso_write_end_clock(struct vdso_clock *vc, bool first)
 {
-	struct vdso_clock *vc = vd->clock_data;
+	if (first)
+		smp_wmb();
 
-	smp_wmb();
 	/*
 	 * WRITE_ONCE() is required otherwise the compiler can validly tear
-	 * updates to vd[x].seq and it is possible that the value seen by the
+	 * updates to vc->seq and it is possible that the value seen by the
 	 * reader is inconsistent.
 	 */
-	WRITE_ONCE(vc[CS_HRES_COARSE].seq, vc[CS_HRES_COARSE].seq + 1);
-	WRITE_ONCE(vc[CS_RAW].seq, vc[CS_RAW].seq + 1);
+	WRITE_ONCE(vc->seq, vc->seq + 1);
+}
+
+static __always_inline void vdso_write_begin(struct vdso_time_data *vd)
+{
+	struct vdso_clock *vc = vd->clock_data;
+
+	vdso_write_begin_clock(&vc[CS_HRES_COARSE], false);
+	vdso_write_begin_clock(&vc[CS_RAW], true);
+}
+
+static __always_inline void vdso_write_end(struct vdso_time_data *vd)
+{
+	struct vdso_clock *vc = vd->clock_data;
+
+	vdso_write_end_clock(&vc[CS_HRES_COARSE], true);
+	vdso_write_end_clock(&vc[CS_RAW], false);
 }
 
 #endif /* !__ASSEMBLY__ */

-- 
2.50.0