[core-for-CI PATCH] PCI: Revert the cfg_access_lock lockdep mechanism

[Imre Deak]

From: Dan Williams <dan.j.williams at intel.com>

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 at intel.com>
Closes: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_134186v1/shard-dg2-1/igt@device_reset@unbind-reset-rebind.html
Cc: Jani Saarinen <jani.saarinen at intel.com>
Cc: Dave Jiang <dave.jiang at intel.com>
Cc: Bjorn Helgaas <bhelgaas at google.com>
Signed-off-by: Dan Williams <dan.j.williams at intel.com>
Reviewed-by: Dave Jiang <dave.jiang at intel.com>
References: https://lore.kernel.org/all/ZlXP5oTnSApiDbD1@ideak-desk.fi.intel.com
References: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/11223
Signed-off-by: Imre Deak <imre.deak at intel.com>

---

This patch replaces [1] and [2], those not actually resolving the issue
described in the first References: link.

[1] https://lore.kernel.org/all/20240529102341.3928968-1-jani.nikula@intel.com
[2] https://lore.kernel.org/all/20240529114901.344655-1-imre.deak@intel.com

 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 30f031de9cfe8..b123da16b63ba 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 59e0949fb079d..35fb1f17a589c 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 8e696e547565c..5fbabb4e3425f 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 5e51b0de4c4b5..08b0d1d9d78b7 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 fb004fd4e8890..cafc5ab1cbcb4 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 */
-- 
2.43.3