PCI/MSI: Prevent recursive locking in pci_msix_write_tph_tag()

pci_msix_write_tph_tag() takes the per device MSI descriptor mutex and then
invokes msi_domain_get_virq(), which takes the same mutex again. That
obviously results in a system hang which is exposed by a softlockup or
lockdep warning.

Move the lock guard after the invocation of msi_domain_get_virq() to fix
this.

[ tglx: Massage changelog by adding a proper explanation and removing the
  	not really useful stacktrace ]

Fixes: d5124a9 ("PCI/MSI: Provide a sane mechanism for TPH")
Reported-by: Jorge Lopez <[email protected]>
Suggested-by: Thomas Gleixner <[email protected]>
Signed-off-by: Himanshu Madhani <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Tested-by: Jorge Lopez <[email protected]>
Link: https://lore.kernel.org/all/[email protected]

Author: hmadhani

drivers/pci/msi/msi.c

@@ -934,10 +934,12 @@ int pci_msix_write_tph_tag(struct pci_dev *pdev, unsigned int index, u16 tag)
 	if (!pdev->msix_enabled)
 		return -ENXIO;
 
-	guard(msi_descs_lock)(&pdev->dev);
 	virq = msi_get_virq(&pdev->dev, index);
 	if (!virq)
 		return -ENXIO;
+
+	guard(msi_descs_lock)(&pdev->dev);
+
 	/*
 	 * This is a horrible hack, but short of implementing a PCI
 	 * specific interrupt chip callback and a huge pile of