Messages in this thread | | | Date | Tue, 10 Oct 2023 06:47:27 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH smp,csd] Throw an error if a CSD lock is stuck for too long |
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On Tue, Oct 10, 2023 at 03:58:43PM +1100, Imran Khan wrote: > Hello Paul, > > On 10/10/2023 3:39 am, Paul E. McKenney wrote: > > On Fri, Oct 06, 2023 at 10:32:07AM +1100, Imran Khan wrote: > >> Hello Paul, > >> > >> On 6/10/2023 3:48 am, Paul E. McKenney wrote: > >>> The CSD lock seems to get stuck in 2 "modes". When it gets stuck > >>> temporarily, it usually gets released in a few seconds, and sometimes > >>> up to one or two minutes. > >>> > >>> If the CSD lock stays stuck for more than several minutes, it never > >>> seems to get unstuck, and gradually more and more things in the system > >>> end up also getting stuck. > >>> > >>> In the latter case, we should just give up, so the system can dump out > >>> a little more information about what went wrong, and, with panic_on_oops > >>> and a kdump kernel loaded, dump a whole bunch more information about > >>> what might have gone wrong. > >>> > >>> Question: should this have its own panic_on_ipistall switch in > >>> /proc/sys/kernel, or maybe piggyback on panic_on_oops in a different > >>> way than via BUG_ON? > >>> > >> panic_on_ipistall (set to 1 by default) looks better option to me. For systems > >> where such delay is acceptable and system can eventually get back to sane state, > >> this option (set to 0 after boot) would prevent crashing the system for > >> apparently benign CSD hangs of long duration. > > > > Good point! How about like the following? > > > > Yes, this looks good. > Just realized that keeping panic_on_ipistall set by default(as suggested earlier > by me) would not follow convention of other similar switches like > hard/softlockup_panic etc. which are 0 by deafault. > So default value of 0 looks better choice for panic_on_ipistall as well.
Plus if a new option is set by default and causes problems, people get (understandably) annoyed. ;-)
> > ------------------------------------------------------------------------ > > > > commit 6bcf3786291b86f13b3e13d51e998737a8009ec3 > > Author: Rik van Riel <riel@surriel.com> > > Date: Mon Aug 21 16:04:09 2023 -0400 > > > > smp,csd: Throw an error if a CSD lock is stuck for too long > > > > The CSD lock seems to get stuck in 2 "modes". When it gets stuck > > temporarily, it usually gets released in a few seconds, and sometimes > > up to one or two minutes. > > > > If the CSD lock stays stuck for more than several minutes, it never > > seems to get unstuck, and gradually more and more things in the system > > end up also getting stuck. > > > > In the latter case, we should just give up, so the system can dump out > > a little more information about what went wrong, and, with panic_on_oops > > and a kdump kernel loaded, dump a whole bunch more information about what > > might have gone wrong. In addition, there is an smp.panic_on_ipistall > > kernel boot parameter that by default retains the old behavior, but when > > set enables the panic after the CSD lock has been stuck for more than > > five minutes. > > > > [ paulmck: Apply Imran Khan feedback. ] > > > > Link: https://urldefense.com/v3/__https://lore.kernel.org/lkml/bc7cc8b0-f587-4451-8bcd-0daae627bcc7@paulmck-laptop/__;!!ACWV5N9M2RV99hQ!PDFpjgGTCPjxqCyusua5IZWkvdWEMf51igFDc-yb9cVK9PYr7FpEE1oGpWp09YK4lc15C2taMdcuEOqyH8k$ > > Signed-off-by: Rik van Riel <riel@surriel.com> > > Signed-off-by: Paul E. McKenney <paulmck@kernel.org> > > Cc: Peter Zijlstra <peterz@infradead.org> > > Cc: Valentin Schneider <vschneid@redhat.com> > > Cc: Juergen Gross <jgross@suse.com> > > Cc: Jonathan Corbet <corbet@lwn.net> > > Cc: Randy Dunlap <rdunlap@infradead.org> > > > Reviewed-by: Imran Khan <imran.f.khan@oracle.com>
Thank you, and I will apply this on my next rebase.
Thanx, Paul
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > > index 0a1731a0f0ef..592935267ce2 100644 > > --- a/Documentation/admin-guide/kernel-parameters.txt > > +++ b/Documentation/admin-guide/kernel-parameters.txt > > @@ -5858,6 +5858,11 @@ > > This feature may be more efficiently disabled > > using the csdlock_debug- kernel parameter. > > > > + smp.panic_on_ipistall= [KNL] > > + If a csd_lock_timeout extends for more than > > + five minutes, panic the system. By default, let > > + CSD-lock acquisition take as long as they take. > > + > > smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices > > smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port > > smsc-ircc2.ircc_sir= [HW] SIR base I/O port > > diff --git a/kernel/smp.c b/kernel/smp.c > > index 8455a53465af..b6a0773a7015 100644 > > --- a/kernel/smp.c > > +++ b/kernel/smp.c > > @@ -170,6 +170,8 @@ static DEFINE_PER_CPU(void *, cur_csd_info); > > > > static ulong csd_lock_timeout = 5000; /* CSD lock timeout in milliseconds. */ > > module_param(csd_lock_timeout, ulong, 0444); > > +static bool panic_on_ipistall; > > +module_param(panic_on_ipistall, bool, 0444); > > > > static atomic_t csd_bug_count = ATOMIC_INIT(0); > > > > @@ -230,6 +232,7 @@ static bool csd_lock_wait_toolong(struct __call_single_data *csd, u64 ts0, u64 * > > } > > > > ts2 = sched_clock(); > > + /* How long since we last checked for a stuck CSD lock.*/ > > ts_delta = ts2 - *ts1; > > if (likely(ts_delta <= csd_lock_timeout_ns || csd_lock_timeout_ns == 0)) > > return false; > > @@ -243,9 +246,17 @@ static bool csd_lock_wait_toolong(struct __call_single_data *csd, u64 ts0, u64 * > > else > > cpux = cpu; > > cpu_cur_csd = smp_load_acquire(&per_cpu(cur_csd, cpux)); /* Before func and info. */ > > + /* How long since this CSD lock was stuck. */ > > + ts_delta = ts2 - ts0; > > pr_alert("csd: %s non-responsive CSD lock (#%d) on CPU#%d, waiting %llu ns for CPU#%02d %pS(%ps).\n", > > - firsttime ? "Detected" : "Continued", *bug_id, raw_smp_processor_id(), ts2 - ts0, > > + firsttime ? "Detected" : "Continued", *bug_id, raw_smp_processor_id(), ts_delta, > > cpu, csd->func, csd->info); > > + /* > > + * 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(panic_on_ipistall && (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)),
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