----- On 17 Aug, 2018, at 06:49, Benjamin Herrenschmidt benh@xxxxxxxxxxxxxxxxxxx wrote:
> This protects enable/disable operations using the state mutex to
> avoid races with, for example, concurrent enables on a bridge.
>
> The bus hierarchy is walked first before taking the lock to
> avoid lock nesting (though it would be ok if we ensured that
> we always nest them bottom-up, it is better to just avoid the
> issue alltogether, especially as we might find cases where
> we want to take it top-down later).
>
> Signed-off-by: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
>
> static void pci_enable_bridge(struct pci_dev *dev)
> {
> struct pci_dev *bridge;
> - int retval;
> + int retval, enabled;
>
> bridge = pci_upstream_bridge(dev);
> if (bridge)
> pci_enable_bridge(bridge);
>
> - if (pci_is_enabled(dev)) {
> - if (!dev->is_busmaster)
> - pci_set_master(dev);
> + /* Already enabled ? */
> + pci_dev_state_lock(dev);
> + enabled = pci_is_enabled(dev);
> + if (enabled && !dev->is_busmaster)
> + pci_set_master(dev);
> + pci_dev_state_unlock(dev);
> + if (enabled)
> return;
> - }
>
This looks complicated too me especially with the double locking. What do you
think about a function doing that check that used an unlocked version of
pcie_set_master?
Like:
dev_state_lock(dev);
enabled = pci_is_enabled(dev);
if (enabled && !dev->is_busmaster)
pci_set_master_unlocked();
pci_dev_state_unlock(dev);
BTW If I remember correctly the code today can set bus mastering multiple
times without checking if already done.
Marta
