Re: Coverity CID 142811: pci_set_vga_state() operands don't affect result

[Bjorn Helgaas <bhelgaas@google.com>]

On Thu, Apr 03, 2014 at 02:43:05PM -0600, Bjorn Helgaas wrote:
> Coverity complains about this in drivers/pci/pci.c:
> 
> CID 142811 (#1 of 1): Operands don't affect result (CONSTANT_EXPRESSION_RESULT)
> result_independent_of_operands: flags & (2U /* 1 << 1 */) &
> (command_bits & 4294967292U /* ~(1 | 2) */) is always 0 regardless of
> the values of its operands. This occurs as the logical operand of if.
> 
> 4128        WARN_ON((flags & PCI_VGA_STATE_CHANGE_DECODES) &
> (command_bits & ~(PCI_COMMAND_IO|PCI_COMMAND_MEMORY)));
> 
> This is a result of 3448a19da479 "vgaarb: use bridges to control VGA
> routing where possible."
> 
> I wonder if that middle "&" was intended to be "&&"?

I propose the following patch for this.  Unless there's objection, I'll
queue this for v3.16.  I took the liberty of interpreting your email
responses as acks.


PCI: Fix incorrect vgaarb conditional in WARN_ON()

From: Bjorn Helgaas <bhelgaas@google.com>

3448a19da479 "vgaarb: use bridges to control VGA routing where possible"
added the "flags & PCI_VGA_STATE_CHANGE_DECODES" condition to an existing
WARN_ON(), but used bitwise AND (&) instead of logical AND (&&), so the
condition is never true.  Replace with logical AND.

Found by Coverity (CID 142811).

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Yinghai Lu <yinghai@kernel.org>
Acked-by: David Airlie <airlied@redhat.com>
---
 drivers/pci/pci.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 7325d43bf030..39012831867e 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -4125,7 +4125,7 @@ int pci_set_vga_state(struct pci_dev *dev, bool decode,
 	u16 cmd;
 	int rc;
 
-	WARN_ON((flags & PCI_VGA_STATE_CHANGE_DECODES) & (command_bits & ~(PCI_COMMAND_IO|PCI_COMMAND_MEMORY)));
+	WARN_ON((flags & PCI_VGA_STATE_CHANGE_DECODES) && (command_bits & ~(PCI_COMMAND_IO|PCI_COMMAND_MEMORY)));
 
 	/* ARCH specific VGA enables */
 	rc = pci_set_vga_state_arch(dev, decode, command_bits, flags);