Mark an emergency section within print_usage_bug(), where
lockdep bugs are printed. In this section, the CPU will not
perform console output for the printk() calls. Instead, a
flushing of the console output is triggered when exiting
the emergency section.
Signed-off-by: John Ogness <[email protected]>
---
kernel/locking/lockdep.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index e85b5ad3e206..00465373d358 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -56,6 +56,7 @@
#include <linux/kprobes.h>
#include <linux/lockdep.h>
#include <linux/context_tracking.h>
+#include <linux/console.h>
#include <asm/sections.h>
@@ -3970,6 +3971,8 @@ print_usage_bug(struct task_struct *curr, struct held_lock *this,
if (!debug_locks_off() || debug_locks_silent)
return;
+ nbcon_cpu_emergency_enter();
+
pr_warn("\n");
pr_warn("================================\n");
pr_warn("WARNING: inconsistent lock state\n");
@@ -3998,6 +4001,8 @@ print_usage_bug(struct task_struct *curr, struct held_lock *this,
pr_warn("\nstack backtrace:\n");
dump_stack();
+
+ nbcon_cpu_emergency_exit();
}
/*
--
2.39.2
On 2/18/24 13:57, John Ogness wrote:
> Mark an emergency section within print_usage_bug(), where
> lockdep bugs are printed. In this section, the CPU will not
> perform console output for the printk() calls. Instead, a
> flushing of the console output is triggered when exiting
> the emergency section.
>
> Signed-off-by: John Ogness <[email protected]>
> ---
> kernel/locking/lockdep.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index e85b5ad3e206..00465373d358 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -56,6 +56,7 @@
> #include <linux/kprobes.h>
> #include <linux/lockdep.h>
> #include <linux/context_tracking.h>
> +#include <linux/console.h>
>
> #include <asm/sections.h>
>
> @@ -3970,6 +3971,8 @@ print_usage_bug(struct task_struct *curr, struct held_lock *this,
> if (!debug_locks_off() || debug_locks_silent)
> return;
>
> + nbcon_cpu_emergency_enter();
> +
> pr_warn("\n");
> pr_warn("================================\n");
> pr_warn("WARNING: inconsistent lock state\n");
> @@ -3998,6 +4001,8 @@ print_usage_bug(struct task_struct *curr, struct held_lock *this,
>
> pr_warn("\nstack backtrace:\n");
> dump_stack();
> +
> + nbcon_cpu_emergency_exit();
> }
>
> /*
lockdep.c has multiple functions that print stuff to the console, like
- print_circular_bug_header()
- print_bad_irq_dependency()
- print_deadlock_bug()
- print_collision()
- print_usage_bug()
- print_irq_inversion_bug()
- print_lock_invalid_wait_context()
- print_lock_nested_lock_not_held()
- print_unlock_imbalance_bug()
- print_lock_contention_bug()
- print_freed_lock_bug()
- print_held_locks_bug()
- lockdep_rcu_suspicious()
So what is special about print_usage_bug() that it needs this emergency
treatment but not the other ones?
Cheers,
Longman
On 2024-02-18, Waiman Long <[email protected]> wrote:
> On 2/18/24 13:57, John Ogness wrote:
> lockdep.c has multiple functions that print stuff to the console, like
>
> - print_circular_bug_header()
> - print_bad_irq_dependency()
> - print_deadlock_bug()
> - print_collision()
> - print_usage_bug()
> - print_irq_inversion_bug()
> - print_lock_invalid_wait_context()
> - print_lock_nested_lock_not_held()
> - print_unlock_imbalance_bug()
> - print_lock_contention_bug()
> - print_freed_lock_bug()
> - print_held_locks_bug()
> - lockdep_rcu_suspicious()
>
> So what is special about print_usage_bug() that it needs this
> emergency treatment but not the other ones?
I do not expect to be able to identify all "emergency printing" paths in
the kernel from the beginning. This series initially marks some sections
that are IMHO interesting for the feature.
As you are implying, for lockdep probably all printing should be
considered emergency. Is it preferred to place the markers outside the
high-level print functions, for example:
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 00465373d358..7a4e4f4a9156 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -2182,10 +2182,12 @@ check_noncircular(struct held_lock *src, struct held_lock *target,
*trace = save_trace();
}
+ nbcon_cpu_emergency_enter();
if (src->class_idx == target->class_idx)
print_deadlock_bug(current, src, target);
else
print_circular_bug(&src_entry, target_entry, src, target);
+ nbcon_cpu_emergency_exit();
}
return ret;
Or is it preferred to put them directly around the various pr_warn()
blocks (as the patch in this series is doing)?
John Ogness
On 2/19/24 06:11, John Ogness wrote:
> On 2024-02-18, Waiman Long <[email protected]> wrote:
>> On 2/18/24 13:57, John Ogness wrote:
>> lockdep.c has multiple functions that print stuff to the console, like
>>
>> - print_circular_bug_header()
>> - print_bad_irq_dependency()
>> - print_deadlock_bug()
>> - print_collision()
>> - print_usage_bug()
>> - print_irq_inversion_bug()
>> - print_lock_invalid_wait_context()
>> - print_lock_nested_lock_not_held()
>> - print_unlock_imbalance_bug()
>> - print_lock_contention_bug()
>> - print_freed_lock_bug()
>> - print_held_locks_bug()
>> - lockdep_rcu_suspicious()
>>
>> So what is special about print_usage_bug() that it needs this
>> emergency treatment but not the other ones?
> I do not expect to be able to identify all "emergency printing" paths in
> the kernel from the beginning. This series initially marks some sections
> that are IMHO interesting for the feature.
That is what I like to see in the changelog. I am aware that this patch
is probably not complete, but you need to set the right expectation that
similar changes will have to be done elsewhere in lockdep to complete
the change. We can make the other necessary changes after this patch
series have been merged. It also helps if you can document what
undesirable thing may happen if printk() is called without setting the
emergency mode.
>
>
> As you are implying, for lockdep probably all printing should be
> considered emergency. Is it preferred to place the markers outside the
> high-level print functions, for example:
>
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index 00465373d358..7a4e4f4a9156 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -2182,10 +2182,12 @@ check_noncircular(struct held_lock *src, struct held_lock *target,
> *trace = save_trace();
> }
>
> + nbcon_cpu_emergency_enter();
> if (src->class_idx == target->class_idx)
> print_deadlock_bug(current, src, target);
> else
> print_circular_bug(&src_entry, target_entry, src, target);
> + nbcon_cpu_emergency_exit();
> }
>
> return ret;
>
> Or is it preferred to put them directly around the various pr_warn()
> blocks (as the patch in this series is doing)?
There are pros and cons for both. It will depend on how expensive is the
nbcon_cpu_emergency_{enter|exit}() call as printing won't happen if
lockdep is turned off somehow. Since lockdep is for debugging and
efficiency isn't that important, putting the emergency enter/exit
markers outside the high level print functions will make it a bit easier
to read.
My 2 cents.
Cheers,
Longman
>
> John Ogness
>
On Sun 2024-02-18 20:03:26, John Ogness wrote:
> Mark an emergency section within print_usage_bug(), where
> lockdep bugs are printed. In this section, the CPU will not
> perform console output for the printk() calls. Instead, a
> flushing of the console output is triggered when exiting
> the emergency section.
>
> Signed-off-by: John Ogness <[email protected]>
The patch looks fine from my POV. Well, I expect that you will send
another version addressing Waiman's concerns.
Best Regards,
Petr