From: Rik van Riel <riel@xxxxxxxxxxx>
About 40% of all csd_lock warnings observed in our fleet appear to
be due to sched_clock() going backward in time (usually only a little
bit), resulting in ts0 being larger than ts2.
When the local CPU is at fault, we should print out a message reflecting
that, rather than trying to get the remote CPU's stack trace.
Signed-off-by: Rik van Riel <riel@xxxxxxxxxxx>
Tested-by: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@xxxxxxxxxx>
---
kernel/smp.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/kernel/smp.c b/kernel/smp.c
index dfcde438ef63..143ae26f96a2 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -253,6 +253,14 @@ static bool csd_lock_wait_toolong(call_single_data_t *csd, u64 ts0, u64 *ts1, in
csd_lock_timeout_ns == 0))
return false;
+ if (ts0 > ts2) {
+ /* Our own sched_clock went backward; don't blame another CPU. */
+ ts_delta = ts0 - ts2;
+ pr_alert("sched_clock on CPU %d went backward by %llu ns\n", raw_smp_processor_id(), ts_delta);
+ *ts1 = ts2;
+ return false;
+ }
+
firsttime = !*bug_id;
if (firsttime)
*bug_id = atomic_inc_return(&csd_bug_count);
--
2.40.1
