Messages in this thread Patch in this message | | | Date | Mon, 16 Oct 2023 17:52:57 -0300 | From | Leonardo Bras <> | Subject | Re: [PATCH smp,csd] Throw an error if a CSD lock is stuck for too long |
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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@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://lore.kernel.org/lkml/bc7cc8b0-f587-4451-8bcd-0daae627bcc7@paulmck-laptop/ > > > 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> > > > > > > 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@redhat.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 :)
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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