From: Rik van Riel <[email protected]> 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 <[email protected]> Tested-by: "Paul E. McKenney" <[email protected]> Signed-off-by: Neeraj Upadhyay <[email protected]> --- 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
