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SubjectRe: [PATCH 2/2] lockdep: warn on redundant or incorrect irq state changes
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On 23/07/2020 20:56, Nicholas Piggin wrote:
> With the previous patch, lockdep hardirq state changes should not be
> redundant. Softirq state changes already follow that pattern.
>
> So warn on unexpected enable-when-enabled or disable-when-disabled
> conditions, to catch possible errors or sloppy patterns that could
> lead to similar bad behavior due to NMIs etc.


This one does not apply anymore as Peter's changes went in already but
this one is not really a fix so I can live with that. Did 1/2 go
anywhere? Thanks,


>
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> ---
> kernel/locking/lockdep.c | 80 +++++++++++++-----------------
> kernel/locking/lockdep_internals.h | 4 --
> kernel/locking/lockdep_proc.c | 10 +---
> 3 files changed, 35 insertions(+), 59 deletions(-)
>
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index 29a8de4c50b9..138458fb2234 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -3649,15 +3649,8 @@ void lockdep_hardirqs_on_prepare(unsigned long ip)
> if (unlikely(!debug_locks || current->lockdep_recursion))
> return;
>
> - if (unlikely(current->hardirqs_enabled)) {
> - /*
> - * Neither irq nor preemption are disabled here
> - * so this is racy by nature but losing one hit
> - * in a stat is not a big deal.
> - */
> - __debug_atomic_inc(redundant_hardirqs_on);
> + if (DEBUG_LOCKS_WARN_ON(current->hardirqs_enabled))
> return;
> - }
>
> /*
> * We're enabling irqs and according to our state above irqs weren't
> @@ -3695,15 +3688,8 @@ void noinstr lockdep_hardirqs_on(unsigned long ip)
> if (unlikely(!debug_locks || curr->lockdep_recursion))
> return;
>
> - if (curr->hardirqs_enabled) {
> - /*
> - * Neither irq nor preemption are disabled here
> - * so this is racy by nature but losing one hit
> - * in a stat is not a big deal.
> - */
> - __debug_atomic_inc(redundant_hardirqs_on);
> + if (DEBUG_LOCKS_WARN_ON(curr->hardirqs_enabled))
> return;
> - }
>
> /*
> * We're enabling irqs and according to our state above irqs weren't
> @@ -3738,6 +3724,9 @@ void noinstr lockdep_hardirqs_off(unsigned long ip)
> if (unlikely(!debug_locks || curr->lockdep_recursion))
> return;
>
> + if (DEBUG_LOCKS_WARN_ON(!curr->hardirqs_enabled))
> + return;
> +
> /*
> * So we're supposed to get called after you mask local IRQs, but for
> * some reason the hardware doesn't quite think you did a proper job.
> @@ -3745,17 +3734,13 @@ void noinstr lockdep_hardirqs_off(unsigned long ip)
> if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
> return;
>
> - if (curr->hardirqs_enabled) {
> - /*
> - * We have done an ON -> OFF transition:
> - */
> - curr->hardirqs_enabled = 0;
> - curr->hardirq_disable_ip = ip;
> - curr->hardirq_disable_event = ++curr->irq_events;
> - debug_atomic_inc(hardirqs_off_events);
> - } else {
> - debug_atomic_inc(redundant_hardirqs_off);
> - }
> + /*
> + * We have done an ON -> OFF transition:
> + */
> + curr->hardirqs_enabled = 0;
> + curr->hardirq_disable_ip = ip;
> + curr->hardirq_disable_event = ++curr->irq_events;
> + debug_atomic_inc(hardirqs_off_events);
> }
> EXPORT_SYMBOL_GPL(lockdep_hardirqs_off);
>
> @@ -3769,6 +3754,9 @@ void lockdep_softirqs_on(unsigned long ip)
> if (unlikely(!debug_locks || current->lockdep_recursion))
> return;
>
> + if (DEBUG_LOCKS_WARN_ON(curr->softirqs_enabled))
> + return;
> +
> /*
> * We fancy IRQs being disabled here, see softirq.c, avoids
> * funny state and nesting things.
> @@ -3776,11 +3764,6 @@ void lockdep_softirqs_on(unsigned long ip)
> if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
> return;
>
> - if (curr->softirqs_enabled) {
> - debug_atomic_inc(redundant_softirqs_on);
> - return;
> - }
> -
> current->lockdep_recursion++;
> /*
> * We'll do an OFF -> ON transition:
> @@ -3809,26 +3792,26 @@ void lockdep_softirqs_off(unsigned long ip)
> if (unlikely(!debug_locks || current->lockdep_recursion))
> return;
>
> + if (DEBUG_LOCKS_WARN_ON(!curr->softirqs_enabled))
> + return;
> +
> /*
> * We fancy IRQs being disabled here, see softirq.c
> */
> if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
> return;
>
> - if (curr->softirqs_enabled) {
> - /*
> - * We have done an ON -> OFF transition:
> - */
> - curr->softirqs_enabled = 0;
> - curr->softirq_disable_ip = ip;
> - curr->softirq_disable_event = ++curr->irq_events;
> - debug_atomic_inc(softirqs_off_events);
> - /*
> - * Whoops, we wanted softirqs off, so why aren't they?
> - */
> - DEBUG_LOCKS_WARN_ON(!softirq_count());
> - } else
> - debug_atomic_inc(redundant_softirqs_off);
> + /*
> + * We have done an ON -> OFF transition:
> + */
> + curr->softirqs_enabled = 0;
> + curr->softirq_disable_ip = ip;
> + curr->softirq_disable_event = ++curr->irq_events;
> + debug_atomic_inc(softirqs_off_events);
> + /*
> + * Whoops, we wanted softirqs off, so why aren't they?
> + */
> + DEBUG_LOCKS_WARN_ON(!softirq_count());
> }
>
> static int
> @@ -5684,6 +5667,11 @@ void __init lockdep_init(void)
>
> printk(" per task-struct memory footprint: %zu bytes\n",
> sizeof(((struct task_struct *)NULL)->held_locks));
> +
> + WARN_ON(irqs_disabled());
> +
> + current->hardirqs_enabled = 1;
> + current->softirqs_enabled = 1;
> }
>
> static void
> diff --git a/kernel/locking/lockdep_internals.h b/kernel/locking/lockdep_internals.h
> index baca699b94e9..6dd8b1f06dc4 100644
> --- a/kernel/locking/lockdep_internals.h
> +++ b/kernel/locking/lockdep_internals.h
> @@ -180,12 +180,8 @@ struct lockdep_stats {
> unsigned int chain_lookup_misses;
> unsigned long hardirqs_on_events;
> unsigned long hardirqs_off_events;
> - unsigned long redundant_hardirqs_on;
> - unsigned long redundant_hardirqs_off;
> unsigned long softirqs_on_events;
> unsigned long softirqs_off_events;
> - unsigned long redundant_softirqs_on;
> - unsigned long redundant_softirqs_off;
> int nr_unused_locks;
> unsigned int nr_redundant_checks;
> unsigned int nr_redundant;
> diff --git a/kernel/locking/lockdep_proc.c b/kernel/locking/lockdep_proc.c
> index 5525cd3ba0c8..98f204220ed9 100644
> --- a/kernel/locking/lockdep_proc.c
> +++ b/kernel/locking/lockdep_proc.c
> @@ -172,12 +172,8 @@ static void lockdep_stats_debug_show(struct seq_file *m)
> #ifdef CONFIG_DEBUG_LOCKDEP
> unsigned long long hi1 = debug_atomic_read(hardirqs_on_events),
> hi2 = debug_atomic_read(hardirqs_off_events),
> - hr1 = debug_atomic_read(redundant_hardirqs_on),
> - hr2 = debug_atomic_read(redundant_hardirqs_off),
> si1 = debug_atomic_read(softirqs_on_events),
> - si2 = debug_atomic_read(softirqs_off_events),
> - sr1 = debug_atomic_read(redundant_softirqs_on),
> - sr2 = debug_atomic_read(redundant_softirqs_off);
> + si2 = debug_atomic_read(softirqs_off_events);
>
> seq_printf(m, " chain lookup misses: %11llu\n",
> debug_atomic_read(chain_lookup_misses));
> @@ -196,12 +192,8 @@ static void lockdep_stats_debug_show(struct seq_file *m)
>
> seq_printf(m, " hardirq on events: %11llu\n", hi1);
> seq_printf(m, " hardirq off events: %11llu\n", hi2);
> - seq_printf(m, " redundant hardirq ons: %11llu\n", hr1);
> - seq_printf(m, " redundant hardirq offs: %11llu\n", hr2);
> seq_printf(m, " softirq on events: %11llu\n", si1);
> seq_printf(m, " softirq off events: %11llu\n", si2);
> - seq_printf(m, " redundant softirq ons: %11llu\n", sr1);
> - seq_printf(m, " redundant softirq offs: %11llu\n", sr2);
> #endif
> }
>
>

--
Alexey

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