On Wed, Jan 18 2023 at 10:22, Johan Hovold wrote:

On Tue, Jan 17, 2023 at 10:23:20PM +0100, Thomas Gleixner wrote:

quoted

On Mon, Jan 16 2023 at 14:50, Johan Hovold wrote:

quoted

The global irq_domain_mutex is now held in all paths that update the
revmap structures so there is no longer any need for the revmap mutex.

This can also go after the 3rd race fix, but ...

quoted

 static void irq_domain_clear_mapping(struct irq_domain *domain,
 				     irq_hw_number_t hwirq)
 {
+	lockdep_assert_held(&irq_domain_mutex);

these lockdep asserts want to be part of the [dis]association race
fixes. They are completely unrelated to the removal of the revmap_mutex.

No, they are very much related to the removal of the revmap_mutex. These
functions deal with the revmap structures which before this patch were
clearly only modified with the revmap_mutex held.

The lockdep assert is here to guarantee that my claim that all current
(and future) paths that end up modifying these structures do so under
the irq_domain_mutex instead.

quoted

Your race fixes change the locking and you want to ensure that all
callers comply right there, no?

I want to make sure that all callers of these function comply, yes.
That's why the asserts belong in this patch.

You can do this in a two step approach.

    1) Add the new locking and ensure that the lock is held when
       the functions are called

    2) Safely remove the revmap_mutex because you already established
       that revmap is protected by some other means

Thanks,

        tglx

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