5.4-stable review patch. If anyone has any objections, please let me know.
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From: Sven Schnelle svens@linux.ibm.com
[ 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 --- arch/s390/kernel/time.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c index 11c32b228f51..0e1925104fcf 100644 --- a/arch/s390/kernel/time.c +++ b/arch/s390/kernel/time.c @@ -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. */