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smp: print only local CPU info when sched_clock goes backward

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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@surriel.com>
Tested-by: "Paul E. McKenney" <paulmck@kernel.org>
Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
This commit is contained in:
Rik van Riel 2024-07-15 13:49:41 -04:00 committed by Neeraj Upadhyay
parent d40760d681
commit 9fbaa44114
1 changed files with 8 additions and 0 deletions
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8
kernel/smp.c
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@ -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);