Re: [PATCH,RFC] smp,csd: throw an error if a CSD lock is stuck for too long
From: Rik van Riel
Date: Wed Sep 13 2023 - 10:34:31 EST
On Wed, 2023-09-13 at 15:22 +0200, Peter Zijlstra wrote:
> On Mon, Aug 21, 2023 at 04:04:09PM -0400, Rik van Riel wrote:
> >
> > + /* How long since this CSD lock was stuck. */
> > + ts_delta = ts2 - ts0;
> >
> > + /*
> > + * If the CSD lock is still stuck after 5 minutes, it is
> > unlikely
> > + * to become unstuck. Use a signed comparison to avoid
> > triggering
> > + * on underflows when the TSC is out of sync between
> > sockets.
> > + */
> > + BUG_ON((s64)ts_delta > 300000000000LL);
> > if (cpu_cur_csd && csd != cpu_cur_csd) {
> > pr_alert("\tcsd: CSD lock (#%d) handling prior
> > %pS(%ps) request.\n",
> > *bug_id, READ_ONCE(per_cpu(cur_csd_func,
> > cpux)),
>
> How are you guys still seeing this? I thought the KVM APIC thing was
> fixed a while ago?
>
It's more fun than that. We're seeing this on bare metal.
Unfortunately, when a system gets wedged that way currently,
it ends up being power cycled automatically, and we aren't
getting crash dumps with clues on what causes the issue.
Doing a BUG_ON() + panic, followed by a kexec into the kdump
kernel will hopefully give us some clues on what might be
causing the issue.
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