From: Rik van Riel <r...@surriel.com>
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 <r...@surriel.com>
Tested-by: "Paul E. McKenney" <paul...@kernel.org>
Signed-off-by: Neeraj Upadhyay <neeraj.upadh...@kernel.org>
---
kernel/smp.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/kernel/smp.c b/kernel/smp.c
index b484ee6dcaf6..f25e20617b7e 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -254,6 +254,14 @@ 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
