Commit ad64d71d authored by Thomas Weißschuh's avatar Thomas Weißschuh Committed by Thomas Gleixner
Browse files

vdso/helpers: Add helpers for seqlocks of single vdso_clock 



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.

[ tglx: Move the SMP memory barriers to the call sites and get rid of the
  	confusing first/last arguments and conditional barriers ]

Signed-off-by: default avatarThomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250701-vdso-auxclock-v1-4-df7d9f87b9b8@linutronix.de
parent 76164ca0

include/vdso/helpers.h

+38 −12
Original line number Diff line number Diff line
@@ -28,17 +28,47 @@ 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_seq_begin(struct vdso_clock *vc)

{

	struct vdso_clock *vc = vd->clock_data;

	/*

	 * WRITE_ONCE() is required otherwise the compiler can validly tear

	 * updates to vc->seq and it is possible that the value seen by the

	 * reader is inconsistent.

	 */

	WRITE_ONCE(vc->seq, vc->seq + 1);

}



static __always_inline void vdso_write_seq_end(struct vdso_clock *vc)

{

	/*

	 * 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_clock(struct vdso_clock *vc)

{

	vdso_write_seq_begin(vc);

	/* Ensure the sequence invalidation is visible before data is modified */

	smp_wmb();

}



static __always_inline void vdso_write_end_clock(struct vdso_clock *vc)

{

	/* Ensure the data update is visible before the sequence is set valid again */

	smp_wmb();

	vdso_write_seq_end(vc);

}



static __always_inline void vdso_write_begin(struct vdso_time_data *vd)

{

	struct vdso_clock *vc = vd->clock_data;



	vdso_write_seq_begin(&vc[CS_HRES_COARSE]);

	vdso_write_seq_begin(&vc[CS_RAW]);

	/* Ensure the sequence invalidation is visible before data is modified */

	smp_wmb();

}
@@ -46,14 +76,10 @@ static __always_inline void vdso_write_end(struct vdso_time_data *vd) 
{

	struct vdso_clock *vc = vd->clock_data;



	/* Ensure the data update is visible before the sequence is set valid again */

	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

	 * 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);

	vdso_write_seq_end(&vc[CS_HRES_COARSE]);

	vdso_write_seq_end(&vc[CS_RAW]);

}



#endif /* !__ASSEMBLY__ */