PCI: Revert the cfg_access_lock lockdep mechanism

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.

Link: https://lore.kernel.org/r/171711746402.1628941.14575335981264103013.stgit@dwillia2-xfh.jf.intel.com
Fixes: 7e89efc ("PCI: Lock upstream bridge for pci_reset_function()")
Reported-by: Imre Deak <[email protected]>
Closes: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_134186v1/shard-dg2-1/igt@[email protected]
Signed-off-by: Dan Williams <[email protected]>
Signed-off-by: Bjorn Helgaas <[email protected]>
Tested-by: Hans de Goede <[email protected]>
Tested-by: Kalle Valo <[email protected]>
Reviewed-by: Dave Jiang <[email protected]>
Cc: Jani Saarinen <[email protected]>

Author: djbw

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);
 

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");

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);

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

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 */