s390/stp: Remove udelay from stp_sync_clock()

[ Upstream commit b367017cdac21781a74eff4e208d3d38e1f38d3f ]

When an stp sync check is handled on a system with multiple
cpus each cpu gets a machine check but only the first one
actually handles the sync operation. All other CPUs spin
waiting for the first one to finish with a short udelay().
But udelay can't be used here as the first CPU modifies tod_clock_base
before performing the sync op. During this timeframe
get_tod_clock_monotonic() might return a non-monotonic time.

The time spent waiting should be very short and udelay is a busy loop
anyways, therefore simply remove the udelay.

Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c
index fed17d407a444209cdc074282de8d5ab2fff3e23..cb7ed55e24d206a9da1b70f93e6d8152f75693b6 100644 (file)
--- a/arch/s390/kernel/time.c
+++ b/arch/s390/kernel/time.c
@@ -580,7 +580,7 @@ static int stp_sync_clock(void *data)
                atomic_dec(&sync->cpus);
                /* Wait for in_sync to be set. */
                while (READ_ONCE(sync->in_sync) == 0)
-                       __udelay(1);
+                       ;
        }
        if (sync->in_sync != 1)
                /* Didn't work. Clear per-cpu in sync bit again. */