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Message-ID: <ZS2j73BWypYk-S1u@redhat.com>
Date: Mon, 16 Oct 2023 17:58:23 -0300
From: Leonardo Bras <leobras@...hat.com>
To: "Paul E. McKenney" <paulmck@...nel.org>
Cc: Imran Khan <imran.f.khan@...cle.com>,
Peter Zijlstra <peterz@...radead.org>,
Valentin Schneider <vschneid@...hat.com>,
Juergen Gross <jgross@...e.com>,
Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH smp,csd] Throw an error if a CSD lock is stuck for too
long
On Mon, Oct 16, 2023 at 05:52:57PM -0300, Leonardo Bras wrote:
> On Mon, Oct 16, 2023 at 11:27:51AM -0700, Paul E. McKenney wrote:
> > On Fri, Oct 13, 2023 at 12:26:22PM -0300, Leonardo Bras wrote:
> > > On Mon, Oct 09, 2023 at 09:39:38AM -0700, 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?
> > > >
> > > > Thanx, Paul
> > > >
> > > > ------------------------------------------------------------------------
> > > >
> > > > commit 6bcf3786291b86f13b3e13d51e998737a8009ec3
> > > > Author: Rik van Riel <riel@...riel.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://lore.kernel.org/lkml/bc7cc8b0-f587-4451-8bcd-0daae627bcc7@paulmck-laptop/
> > > > Signed-off-by: Rik van Riel <riel@...riel.com>
> > > > Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> > > > Cc: Peter Zijlstra <peterz@...radead.org>
> > > > Cc: Valentin Schneider <vschneid@...hat.com>
> > > > Cc: Juergen Gross <jgross@...e.com>
> > > > Cc: Jonathan Corbet <corbet@....net>
> > > > Cc: Randy Dunlap <rdunlap@...radead.org>
> > > >
> > > > 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.
> > > > +
> > >
> > > It could be interesting to have it as an s64 parameter (in {mili,}seconds)
> > > instead of bool, this way the user could pick the time to wait before the
> > > panic happens. 0 or -1 could mean disabled.
> > >
> > > What do you think?
> > >
> > > Other than that,
> > > Reviewed-by: Leonardo Bras <leobras@...hat.com>
> >
> > Thank you for looking this over!
> >
> > How about with the diff shown below, to be folded into the original?
> > I went with int instead of s64 because I am having some difficulty
> > imagining anyone specifying more than a 24-day timeout. ;-)
>
> I suggested s64 just because it was the type being used in
> BUG_ON(panic_on_ipistall && (s64)ts_delta > 300000000000LL);
>
> But anyway, int should be fine.
>
>
> >
> > Thanx, Paul
> >
> > ------------------------------------------------------------------------
> >
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > index ccb7621eff79..ea5ae9deb753 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -5931,8 +5931,10 @@
> >
> > 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.
> > + the specified number of milliseconds, panic the
> > + system. By default, let CSD-lock acquisition
> > + take as long as they take. Specifying 300,000
> > + for this value provides a 10-minute timeout.
>
> 300,000 ms is 300s, which is 5 minutes, right?
>
> >
> > smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
> > smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
> > diff --git a/kernel/smp.c b/kernel/smp.c
> > index b6a0773a7015..d3ca47f32f38 100644
> > --- a/kernel/smp.c
> > +++ b/kernel/smp.c
> > @@ -170,8 +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 int panic_on_ipistall; /* CSD panic timeout in milliseconds, 300000 for ten minutes. */
>
> s/ten/five
>
> > +module_param(panic_on_ipistall, int, 0444);
> >
> > static atomic_t csd_bug_count = ATOMIC_INIT(0);
> >
> > @@ -256,7 +256,7 @@ static bool csd_lock_wait_toolong(struct __call_single_data *csd, u64 ts0, u64 *
> > * 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);
> > + BUG_ON(panic_on_ipistall > 0 && (s64)ts_delta > ((s64)panic_on_ipistall * NSEC_PER_MSEC));
>
> s64 here would avoid casting (s64)panic_on_ipistall, but I think it does
> not really impact readability.
>
> IIUC ts_delta is an u64 being casted as s64, which could be an issue but no
> computer system will actually take over 2^31 ns (292 years) to run 1
> iteration, so it's safe.
>
> I think it's a nice feaure :)
s/feaure/feature
Also, FWIW:
Reviewed-by: Leonardo Bras <leobras@...hat.com>
>
> Thanks!
> Leo
>
>
> > 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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