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SubjectRe: [PATCH rcu 04/11] kernel/smp: Provide boot-time timeout for CSD lock diagnostics
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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@surriel.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Cc: Juergen Gross <jgross@suse.com>
> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> ---
> 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@suse.com>


Juergen
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