linux-kernel - [PATCH 4/5] PCI: don't touch enable_cnt in pci_device

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Date:	Fri, 18 Jan 2013 15:42:26 +0400
From:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
To:	linux-kernel@...r.kernel.org
Cc:	e1000-devel@...ts.sourceforge.net, linux-pci@...r.kernel.org,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Khalid Aziz <khalid.aziz@...com>
Subject: [PATCH 4/5] PCI: don't touch enable_cnt in pci_device_shutdown()

comment in commit b566a22c23327f18ce941ffad0ca907e50a53d41
("PCI: disable Bus Master on PCI device shutdown") says:

| Disable Bus Master bit on the device in pci_device_shutdown() to ensure PCI
| devices do not continue to DMA data after shutdown.  This can cause memory
| corruption in case of a kexec where the current kernel shuts down and
| transfers control to a new kernel while a PCI device continues to DMA to
| memory that does not belong to it any more in the new kernel.

Seems like pci_clear_master() must be used here instead of pci_disable_device(),
because it disables Bus Muster unconditionally and doesn't changes enable_cnt.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@...nvz.org>
Cc: linux-pci@...r.kernel.org
Cc: Bjorn Helgaas <bhelgaas@...gle.com>
Cc: Khalid Aziz <khalid.aziz@...com>
---
 drivers/pci/pci-driver.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
index 030dbf0..853d605 100644
--- a/drivers/pci/pci-driver.c
+++ b/drivers/pci/pci-driver.c
@@ -392,7 +392,7 @@ static void pci_device_shutdown(struct device *dev)
 	 * Turn off Bus Master bit on the device to tell it to not
 	 * continue to do DMA
 	 */
-	pci_disable_device(pci_dev);
+	pci_clear_master(pci_dev);
 }
 
 #ifdef CONFIG_PM

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