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s390/stp: Remove udelay from stp_sync_clock()

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[ 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>
This commit is contained in:
Sven Schnelle 2025-07-03 13:50:27 +02:00 • committed by Greg Kroah-Hartman
commit 0c02d35d67
1 changed files with 1 additions and 1 deletions
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2
arch/s390/kernel/time.c
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@ -642,7 +642,7 @@ 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. */