On 2015/5/21 3:47, Bjorn Helgaas wrote:
> I think we have some issues with the e1000e usage of
> pci_disable_link_state_locked(), which Yinghai added with 9f728f53dd70
> ("PCI/e1000e: Add and use pci_disable_link_state_locked()").
>
> That fixed an AER deadlock in the following path, where pci_bus_sem is held
> by pci_walk_bus(), and we deadlocked when we tried to re-acquire it in
> pci_disable_link_state():
>
> do_recovery
> broadcast_error_message(..., report_slot_reset)
> pci_walk_bus
> down_read(&pci_bus_sem)
> cb(...) # report_slot_reset
> report_slot_reset
> dev->driver->err_handler->slot_reset # e1000_io_slot_reset
> e1000_io_slot_reset
> e1000e_disable_aspm
> pci_disable_link_state
> down_read(&pci_bus_sem)
>
> 9f728f53dd70 fixed that by changing e1000e_disable_aspm() to use
> pci_disable_link_state_locked() instead, which assumes pci_bus_sem is
> already held.
>
> That's fine for the e1000_io_slot_reset() path, where pci_bus_sem really
> *is* held. But e1000e_disable_aspm() is also called from e1000_probe() and
> __e1000_resume(), and in those paths, we *don't* hold pci_bus_sem.
>
> In effect, the caller of pci_disable_link_state_locked() is promising that
> pci_bus_sem is held, and __pci_disable_link_state() relies on that promise
> for its locking. But e1000e isn't upholding its end of the bargain.
>
> I'm not 100% sure __pci_disable_link_state() actually *needs* that locking:
> it is only called from a driver, and it should be impossible for a device
pci_disable_link_state()/pci_disable_link_state_locked() almost always be called in drivers,
one exception is a quirk function quirk_disable_aspm_l0s(). Since the final fixup is called
in pci_bus_add_device(), and we have big lock pci_rescan_remove_lock to protect the add/remove,
so I think it's still safe to call pci_disable_link_state() in quirk_disable_aspm_l0s() without
the pci_bus_sem lock.
/*
* The 82575 and 82598 may experience data corruption issues when transitioning
* out of L0S. To prevent this we need to disable L0S on the pci-e link
*/
static void quirk_disable_aspm_l0s(struct pci_dev *dev)
{
dev_info(&dev->dev, "Disabling L0s\n");
pci_disable_link_state(dev, PCIE_LINK_STATE_L0S);
}
DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_INTEL, 0x10a7, quirk_disable_aspm_l0s);
...
> or any upstream bridge to go away while a driver is bound to it. If
> somebody wanted to analyze this further and propose a patch to remove the
> locking (if it seems safe), that would be great.
>
> But in any case, __pci_disable_link_state() should be able to rely on its
> callers following the rules, so I'd like to see an e1000e change to use
> pci_disable_link_state() from the paths where pci_bus_sem is not held.
>
> Bjorn
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--
Thanks!
Yijing
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