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PCI: Avoid possible deadlock on pci_lock and p->pi_lock

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pci_lock is an IRQ-safe spinlock that protects all accesses to PCI
configuration space (see PCI_OP_READ() and PCI_OP_WRITE() in pci/access.c).

The pci_cfg_access_unlock() path acquires pci_lock, then p->pi_lock (inside
wake_up_all()).  According to lockdep, there is a possible path involving
snbep_uncore_pci_read_counter() that could acquire them in the reverse
order: acquiring p->pi_lock, then pci_lock, which could result in a
deadlock.  Lockdep details are in the bugzilla below.

Avoid the possible deadlock by dropping pci_lock before waking up any
config access waiters.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=192901
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
This commit is contained in:
Bjorn Helgaas 2017-01-13 18:05:12 -06:00
parent 53762ba810
commit cdcb33f982
1 changed files with 2 additions and 1 deletions
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3
drivers/pci/access.c
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@ -684,8 +684,9 @@ void pci_cfg_access_unlock(struct pci_dev *dev)
WARN_ON(!dev->block_cfg_access);
dev->block_cfg_access = 0;
wake_up_all(&pci_cfg_wait);
raw_spin_unlock_irqrestore(&pci_lock, flags);
wake_up_all(&pci_cfg_wait);
}
EXPORT_SYMBOL_GPL(pci_cfg_access_unlock);