Re: [PATCH 03/19] lockdep: improve scenario messages for RECLAIM_FS errors.

Peter Zijlstra
2014-04-16T07:22:12Z

On Wed, Apr 16, 2014 at 02:03:36PM +1000, NeilBrown wrote:
> lockdep can check for locking problems involving reclaim using
> the same infrastructure as used for interrupts.
>
> However a number of the messages still refer to interrupts even
> if it was actually a reclaim-related problem.
>
> So determine where the problem was caused by reclaim or irq and adjust
> messages accordingly.
>
> Signed-off-by: NeilBrown <neilb@suse.de>
> ---
> kernel/locking/lockdep.c | 43 ++++++++++++++++++++++++++++++++-----------
> 1 file changed, 32 insertions(+), 11 deletions(-)
>
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index e05b82e92373..33d2ac7519dc 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -1423,7 +1423,8 @@ static void
> print_irq_lock_scenario(struct lock_list *safe_entry,
> struct lock_list *unsafe_entry,
> struct lock_class *prev_class,
> - struct lock_class *next_class)
> + struct lock_class *next_class,
> + int reclaim)

I would rather we just pass enum lock_usage_bit along from the
callsites.

> {
> struct lock_class *safe_class = safe_entry->class;
> struct lock_class *unsafe_class = unsafe_entry->class;

> @@ -1487,6 +1495,8 @@ print_bad_irq_dependency(struct task_struct *curr,
> enum lock_usage_bit bit2,
> const char *irqclass)
> {
> + int reclaim = strncmp(irqclass, "RECLAIM", 7) == 0;
> +

irqclass := state_name(bit2), so instead of relying on the unreliable,
why not use the lock_usage_bit ?

> if (!debug_locks_off_graph_unlock() || debug_locks_silent)
> return 0;
>
> @@ -1528,7 +1538,7 @@ print_bad_irq_dependency(struct task_struct *curr,
>
> printk("\nother info that might help us debug this:\n\n");
> print_irq_lock_scenario(backwards_entry, forwards_entry,
> - hlock_class(prev), hlock_class(next));
> + hlock_class(prev), hlock_class(next), reclaim);

So that would become bit2.

>
> lockdep_print_held_locks(curr);
>
> @@ -2200,7 +2210,7 @@ static void check_chain_key(struct task_struct *curr)
> }
>
> static void
> -print_usage_bug_scenario(struct held_lock *lock)
> +print_usage_bug_scenario(struct held_lock *lock, enum lock_usage_bit new_bit)

Like you did here.

> {
> struct lock_class *class = hlock_class(lock);
>
> @@ -2210,7 +2220,11 @@ print_usage_bug_scenario(struct held_lock *lock)
> printk(" lock(");
> __print_lock_name(class);
> printk(");\n");
> - printk(" <Interrupt>\n");
> + if (new_bit == LOCK_USED_IN_RECLAIM_FS ||
> + new_bit == LOCK_USED_IN_RECLAIM_FS_READ)

And if we're going to do this all over, we might want a helper for this
condition.

> + printk(" <Memory allocation/reclaim>\n");
> + else
> + printk(" <Interrupt>\n");
> printk(" lock(");
> __print_lock_name(class);
> printk(");\n");

Same for the rest I think..