Patch "PCI: Avoid possible deadlock on pci_lock and p->pi_lock" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

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

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
pci-avoid-possible-deadlock-on-pci_lock-and-p-pi_lock.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Bjorn Helgaas <[email protected]>
Date: Sat, 7 Oct 2017 22:37:34 +0000
Subject: PCI: Avoid possible deadlock on pci_lock and p->pi_lock

From: Bjorn Helgaas <[email protected]>

[ Upstream commit cdcb33f9824429a926b971bf041a6cec238f91ff ]

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.

---
 drivers/pci/access.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

@@ -672,8 +672,9 @@ void pci_cfg_access_unlock(struct pci_de
 	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);
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/pci-msi-return-failure-when-msix_setup_entries-fails.patch queue-4.9/pci-avoid-possible-deadlock-on-pci_lock-and-p-pi_lock.patch