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PCI: Revert the cfg_access_lock lockdep mechanism

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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: 7e89efc6e9 ("PCI: Lock upstream bridge for pci_reset_function()")
Reported-by: Imre Deak <imre.deak@intel.com>
Closes: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_134186v1/shard-dg2-1/igt@device_reset@unbind-reset-rebind.html
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Hans de Goede <hdegoede@redhat.com>
Tested-by: Kalle Valo <kvalo@kernel.org>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Cc: Jani Saarinen <jani.saarinen@intel.com>
This commit is contained in:
Dan Williams 2024-05-30 18:04:24 -07:00 committed by Bjorn Helgaas
parent 1613e604df
commit c9d52fb313
5 changed files with 0 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
drivers/pci/access.c
View File

@ -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);

1
drivers/pci/pci.c
View File

@ -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");

3
drivers/pci/probe.c
View File

@ -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);

5
include/linux/lockdep.h
View File

@ -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

2
include/linux/pci.h
View File

@ -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 */