On 5/30/24 6:04 PM, Dan Williams wrote:
> While the experiment did reveal that there are additional places that
> are missing the lock during secondary bus reset, one of the places that
> needs to take cfg_access_lock (pci_bus_lock()) is not prepared for
> lockdep annotation.
>
> Specifically, pci_bus_lock() takes pci_dev_lock() recursively and is
> currently dependent on the fact that the device_lock() is marked
> lockdep_set_novalidate_class(&dev->mutex). Otherwise, without that
> annotation, pci_bus_lock() would need to use something like a new
> pci_dev_lock_nested() helper, a scheme to track a PCI device's depth in
> the topology, and a hope that the depth of a PCI tree never exceeds the
> max value for a lockdep subclass.
>
> The alternative to ripping out the lockdep coverage would be to deploy a
> dynamic lock key for every PCI device. Unfortunately, there is evidence
> that increasing the number of keys that lockdep needs to track to be
> per-PCI-device is prohibitively expensive for something like the
> cfg_access_lock.
>
> The main motivation for adding the annotation in the first place was to
> catch unlocked secondary bus resets, not necessarily catch lock ordering
> problems between cfg_access_lock and other locks. Solve that narrower
> problem with follow-on patches, and just due to targeted revert for now.
>
> Fixes: 7e89efc6e9e4 ("PCI: Lock upstream bridge for pci_reset_function()")
> Reported-by: Imre Deak <imre.deak@xxxxxxxxx>
> Closes: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_134186v1/shard-dg2-1/igt@device_reset@xxxxxxxxxxxxxxxxxxxxxxxx
> Cc: Jani Saarinen <jani.saarinen@xxxxxxxxx>
> Cc: Dave Jiang <dave.jiang@xxxxxxxxx>
> Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Reviewed-by: Dave Jiang <dave.jiang@xxxxxxxxx>
> ---
> drivers/pci/access.c | 4 ----
> drivers/pci/pci.c | 1 -
> drivers/pci/probe.c | 3 ---
> include/linux/lockdep.h | 5 -----
> include/linux/pci.h | 2 --
> 5 files changed, 15 deletions(-)
>
> diff --git a/drivers/pci/access.c b/drivers/pci/access.c
> index 30f031de9cfe..b123da16b63b 100644
> --- a/drivers/pci/access.c
> +++ b/drivers/pci/access.c
> @@ -289,8 +289,6 @@ void pci_cfg_access_lock(struct pci_dev *dev)
> {
> might_sleep();
>
> - lock_map_acquire(&dev->cfg_access_lock);
> -
> raw_spin_lock_irq(&pci_lock);
> if (dev->block_cfg_access)
> pci_wait_cfg(dev);
> @@ -345,8 +343,6 @@ void pci_cfg_access_unlock(struct pci_dev *dev)
> raw_spin_unlock_irqrestore(&pci_lock, flags);
>
> wake_up_all(&pci_cfg_wait);
> -
> - lock_map_release(&dev->cfg_access_lock);
> }
> EXPORT_SYMBOL_GPL(pci_cfg_access_unlock);
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 59e0949fb079..35fb1f17a589 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -4883,7 +4883,6 @@ void __weak pcibios_reset_secondary_bus(struct pci_dev *dev)
> */
> int pci_bridge_secondary_bus_reset(struct pci_dev *dev)
> {
> - lock_map_assert_held(&dev->cfg_access_lock);
> pcibios_reset_secondary_bus(dev);
>
> return pci_bridge_wait_for_secondary_bus(dev, "bus reset");
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 8e696e547565..5fbabb4e3425 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -2546,9 +2546,6 @@ void pci_device_add(struct pci_dev *dev, struct pci_bus *bus)
> dev->dev.dma_mask = &dev->dma_mask;
> dev->dev.dma_parms = &dev->dma_parms;
> dev->dev.coherent_dma_mask = 0xffffffffull;
> - lockdep_register_key(&dev->cfg_access_key);
> - lockdep_init_map(&dev->cfg_access_lock, dev_name(&dev->dev),
> - &dev->cfg_access_key, 0);
>
> dma_set_max_seg_size(&dev->dev, 65536);
> dma_set_seg_boundary(&dev->dev, 0xffffffff);
> diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
> index 5e51b0de4c4b..08b0d1d9d78b 100644
> --- a/include/linux/lockdep.h
> +++ b/include/linux/lockdep.h
> @@ -297,9 +297,6 @@ extern void lock_unpin_lock(struct lockdep_map *lock, struct pin_cookie);
> .wait_type_inner = _wait_type, \
> .lock_type = LD_LOCK_WAIT_OVERRIDE, }
>
> -#define lock_map_assert_held(l) \
> - lockdep_assert(lock_is_held(l) != LOCK_STATE_NOT_HELD)
> -
> #else /* !CONFIG_LOCKDEP */
>
> static inline void lockdep_init_task(struct task_struct *task)
> @@ -391,8 +388,6 @@ extern int lockdep_is_held(const void *);
> #define DEFINE_WAIT_OVERRIDE_MAP(_name, _wait_type) \
> struct lockdep_map __maybe_unused _name = {}
>
> -#define lock_map_assert_held(l) do { (void)(l); } while (0)
> -
> #endif /* !LOCKDEP */
>
> #ifdef CONFIG_PROVE_LOCKING
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index fb004fd4e889..cafc5ab1cbcb 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -413,8 +413,6 @@ struct pci_dev {
> struct resource driver_exclusive_resource; /* driver exclusive resource ranges */
>
> bool match_driver; /* Skip attaching driver */
> - struct lock_class_key cfg_access_key;
> - struct lockdep_map cfg_access_lock;
>
> unsigned int transparent:1; /* Subtractive decode bridge */
> unsigned int io_window:1; /* Bridge has I/O window */
>
