[PATCH] PCI: Allow MSI to work on kexec kernel

We recently ran into a problem where the e1000 device failed to
work properly on the kexec kernel. MSI was enabled for the
device in the main kernel when it crashed. The e1000 driver
tried to enable MSI on the kexec kernel, but the code bailed
early when it found that MSI was already enabled in the hardware,
even though the software state was not properly set up in the
kexec'd kernel. This patch fixes the problem by moving the
early return to after making sure that the software state
is properly initialized.
Signed-off-by: NRajesh Shah <rajesh.shah@intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/pci/msi.c

@@ -940,14 +940,13 @@ int pci_enable_msi(struct pci_dev* dev)
 	if (!pos)
 		return -EINVAL;
 
-	pci_read_config_word(dev, msi_control_reg(pos), &control);
-	if (control & PCI_MSI_FLAGS_ENABLE)
-		return 0;			/* Already in MSI mode */
-
 	if (!msi_lookup_vector(dev, PCI_CAP_ID_MSI)) {
 		/* Lookup Sucess */
 		unsigned long flags;
 
+		pci_read_config_word(dev, msi_control_reg(pos), &control);
+		if (control & PCI_MSI_FLAGS_ENABLE)
+			return 0;	/* Already in MSI mode */
 		spin_lock_irqsave(&msi_lock, flags);
 		if (!vector_irq[dev->irq]) {
 			msi_desc[dev->irq]->msi_attrib.state = 0;