linux-kernel - [PATCH 5.11 014/120] s390/pci: remove superfluous zdev->zbus check

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Date:   Mon, 22 Mar 2021 13:26:37 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, kernel test robot <lkp@...el.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Niklas Schnelle <schnelle@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>
Subject: [PATCH 5.11 014/120] s390/pci: remove superfluous zdev->zbus check

From: Niklas Schnelle <schnelle@...ux.ibm.com>

commit e1bff843cde62a45a287b7f9b4cd5e824e8e49e2 upstream.

Checking zdev->zbus for NULL in __zpci_event_availability() is
superfluous as it can never be NULL at this point. While harmless this
check causes smatch warnings because we later access zdev->zbus with
only having checked zdev != NULL which is sufficient.

The reason zdev->zbus can never be NULL is since with zdev != NULL given
we know the zdev came from get_zdev_by_fid() and thus the zpci_list.
Now on first glance at zpci_create_device() one may assume that there is
a window where the zdev is in the list without a zdev, however this
window can't overlap with __zpci_event_availability() as
zpci_create_device() either runs on the same kthread as part of
availability events, or during the initial CLP List PCI at which point
the __zpci_event_availability() is not yet called as zPCI is not yet
initialized.

Reported-by: kernel test robot <lkp@...el.com>
Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@...ux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/s390/pci/pci_event.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/s390/pci/pci_event.c
+++ b/arch/s390/pci/pci_event.c
@@ -80,7 +80,7 @@ static void __zpci_event_availability(st
 	enum zpci_state state;
 	int ret;

-	if (zdev && zdev->zbus && zdev->zbus->bus)
+	if (zdev && zdev->zbus->bus)
 		pdev = pci_get_slot(zdev->zbus->bus, zdev->devfn);

 	zpci_err("avail CCDF:\n");