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Date: Tue, 5 Mar 2019 15:44:42 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Alex Williamson <alex.williamson@...hat.com>
Cc: linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
hch@....de, okaya@...nel.org, myron.stowe@...hat.com
Subject: Re: [PATCH v2] PCI: Fix "try" semantics of bus and slot reset
On Mon, Feb 18, 2019 at 12:46:46PM -0700, Alex Williamson wrote:
> The commit referenced below introduced device locking around save and
> restore of state for each device during a PCI bus "try" reset, making
> it decidely non-"try" and prone to deadlock in the event that a device
> is already locked. Restore __pci_reset_bus() and __pci_reset_slot()
> to their advertised locking semantics by pushing the save and restore
> functions into the branch where the entire tree is already locked.
> Extend the helper function names with "_locked" and update the comment
> to reflect this calling requirement.
>
> Fixes: b014e96d1abb ("PCI: Protect pci_error_handlers->reset_notify() usage with device_lock()")
> Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
Applied with Sinan's reviewed-by to pci/misc for v5.1, thanks, Alex!
> ---
> drivers/pci/pci.c | 54 ++++++++++++++++++++++++++---------------------------
> 1 file changed, 26 insertions(+), 28 deletions(-)
>
> v2: White space only fix suggested by Myron Stowe, removing an additional
> empty line from __pci_reset_slot() after the restore call is moved.
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index c25acace7d91..2fb149216cde 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -5058,39 +5058,42 @@ static int pci_slot_trylock(struct pci_slot *slot)
> return 0;
> }
>
> -/* Save and disable devices from the top of the tree down */
> -static void pci_bus_save_and_disable(struct pci_bus *bus)
> +/*
> + * Save and disable devices from the top of the tree down while holding
> + * the @dev mutex lock for the entire tree.
> + */
> +static void pci_bus_save_and_disable_locked(struct pci_bus *bus)
> {
> struct pci_dev *dev;
>
> list_for_each_entry(dev, &bus->devices, bus_list) {
> - pci_dev_lock(dev);
> pci_dev_save_and_disable(dev);
> - pci_dev_unlock(dev);
> if (dev->subordinate)
> - pci_bus_save_and_disable(dev->subordinate);
> + pci_bus_save_and_disable_locked(dev->subordinate);
> }
> }
>
> /*
> - * Restore devices from top of the tree down - parent bridges need to be
> - * restored before we can get to subordinate devices.
> + * Restore devices from top of the tree down while holding @dev mutex lock
> + * for the entire tree. Parent bridges need to be restored before we can
> + * get to subordinate devices.
> */
> -static void pci_bus_restore(struct pci_bus *bus)
> +static void pci_bus_restore_locked(struct pci_bus *bus)
> {
> struct pci_dev *dev;
>
> list_for_each_entry(dev, &bus->devices, bus_list) {
> - pci_dev_lock(dev);
> pci_dev_restore(dev);
> - pci_dev_unlock(dev);
> if (dev->subordinate)
> - pci_bus_restore(dev->subordinate);
> + pci_bus_restore_locked(dev->subordinate);
> }
> }
>
> -/* Save and disable devices from the top of the tree down */
> -static void pci_slot_save_and_disable(struct pci_slot *slot)
> +/*
> + * Save and disable devices from the top of the tree down while holding
> + * the @dev mutex lock for the entire tree.
> + */
> +static void pci_slot_save_and_disable_locked(struct pci_slot *slot)
> {
> struct pci_dev *dev;
>
> @@ -5099,26 +5102,25 @@ static void pci_slot_save_and_disable(struct pci_slot *slot)
> continue;
> pci_dev_save_and_disable(dev);
> if (dev->subordinate)
> - pci_bus_save_and_disable(dev->subordinate);
> + pci_bus_save_and_disable_locked(dev->subordinate);
> }
> }
>
> /*
> - * Restore devices from top of the tree down - parent bridges need to be
> - * restored before we can get to subordinate devices.
> + * Restore devices from top of the tree down while holding @dev mutex lock
> + * for the entire tree. Parent bridges need to be restored before we can
> + * get to subordinate devices.
> */
> -static void pci_slot_restore(struct pci_slot *slot)
> +static void pci_slot_restore_locked(struct pci_slot *slot)
> {
> struct pci_dev *dev;
>
> list_for_each_entry(dev, &slot->bus->devices, bus_list) {
> if (!dev->slot || dev->slot != slot)
> continue;
> - pci_dev_lock(dev);
> pci_dev_restore(dev);
> - pci_dev_unlock(dev);
> if (dev->subordinate)
> - pci_bus_restore(dev->subordinate);
> + pci_bus_restore_locked(dev->subordinate);
> }
> }
>
> @@ -5177,17 +5179,15 @@ static int __pci_reset_slot(struct pci_slot *slot)
> if (rc)
> return rc;
>
> - pci_slot_save_and_disable(slot);
> -
> if (pci_slot_trylock(slot)) {
> + pci_slot_save_and_disable_locked(slot);
> might_sleep();
> rc = pci_reset_hotplug_slot(slot->hotplug, 0);
> + pci_slot_restore_locked(slot);
> pci_slot_unlock(slot);
> } else
> rc = -EAGAIN;
>
> - pci_slot_restore(slot);
> -
> return rc;
> }
>
> @@ -5273,17 +5273,15 @@ static int __pci_reset_bus(struct pci_bus *bus)
> if (rc)
> return rc;
>
> - pci_bus_save_and_disable(bus);
> -
> if (pci_bus_trylock(bus)) {
> + pci_bus_save_and_disable_locked(bus);
> might_sleep();
> rc = pci_bridge_secondary_bus_reset(bus->self);
> + pci_bus_restore_locked(bus);
> pci_bus_unlock(bus);
> } else
> rc = -EAGAIN;
>
> - pci_bus_restore(bus);
> -
> return rc;
> }
>
>
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