On Tue, Apr 19, 2022 at 09:11:46AM +0200, Juergen Gross wrote:
> On 19.04.22 00:53, Paul E. McKenney wrote:
> > Debugging of problems involving insanely long-running SMI handlers
> > proceeds better if the CSD-lock timeout can be adjusted. This commit
> > therefore provides a new smp.csd_lock_timeout kernel boot parameter
> > that specifies the timeout in milliseconds. The default remains at the
> > previously hard-coded value of five seconds.
> >
> > Cc: Rik van Riel <riel@xxxxxxxxxxx>
> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> > Cc: Juergen Gross <jgross@xxxxxxxx>
> > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
> > ---
> > Documentation/admin-guide/kernel-parameters.txt | 11 +++++++++++
> > kernel/smp.c | 7 +++++--
> > 2 files changed, 16 insertions(+), 2 deletions(-)
> >
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > index 3f1cc5e317ed..645c4c001b16 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -5377,6 +5377,17 @@
> > smart2= [HW]
> > Format: <io1>[,<io2>[,...,<io8>]]
> > + smp.csd_lock_timeout= [KNL]
> > + Specify the period of time in milliseconds
> > + that smp_call_function() and friends will wait
> > + for a CPU to release the CSD lock. This is
> > + useful when diagnosing bugs involving CPUs
> > + disabling interrupts for extended periods
> > + of time. Defaults to 5,000 milliseconds, and
> > + setting a value of zero disables this feature.
> > + This feature may be more efficiently disabled
> > + using the csdlock_debug- kernel parameter.
> > +
> > 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 01a7c1706a58..d82439bac401 100644
> > --- a/kernel/smp.c
> > +++ b/kernel/smp.c
> > @@ -183,7 +183,9 @@ static DEFINE_PER_CPU(smp_call_func_t, cur_csd_func);
> > static DEFINE_PER_CPU(void *, cur_csd_info);
> > static DEFINE_PER_CPU(struct cfd_seq_local, cfd_seq_local);
> > -#define CSD_LOCK_TIMEOUT (5ULL * NSEC_PER_SEC)
> > +static ulong csd_lock_timeout = 5000; /* CSD lock timeout in milliseconds. */
> > +module_param(csd_lock_timeout, ulong, 0444);
> > +
> > static atomic_t csd_bug_count = ATOMIC_INIT(0);
> > static u64 cfd_seq;
> > @@ -329,6 +331,7 @@ static bool csd_lock_wait_toolong(struct __call_single_data *csd, u64 ts0, u64 *
> > u64 ts2, ts_delta;
> > call_single_data_t *cpu_cur_csd;
> > unsigned int flags = READ_ONCE(csd->node.u_flags);
> > + unsigned long long csd_lock_timeout_ns = csd_lock_timeout * NSEC_PER_MSEC;
> > if (!(flags & CSD_FLAG_LOCK)) {
> > if (!unlikely(*bug_id))
> > @@ -341,7 +344,7 @@ static bool csd_lock_wait_toolong(struct __call_single_data *csd, u64 ts0, u64 *
> > ts2 = sched_clock();
> > ts_delta = ts2 - *ts1;
> > - if (likely(ts_delta <= CSD_LOCK_TIMEOUT))
> > + if (likely(ts_delta <= csd_lock_timeout_ns || csd_lock_timeout_ns <= 0))
>
> csd_lock_timeout_ns is unsigned, so "csd_lock_timeout_ns <= 0" should be rather
> "csd_lock_timeout_ns == 0".
>
> With that fixed you can add my
>
> Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
Thank you, and will do on next rebase.
Thanx, Paul
