linux-kernel - [PATCH AUTOSEL 4.14 08/25] media: cobalt: fix race condition in setting HPD

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Message-Id: <20210704231123.1491517-8-sashal@kernel.org>
Date:   Sun,  4 Jul 2021 19:11:06 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Hans Verkuil <hverkuil-cisco@...all.nl>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Sasha Levin <sashal@...nel.org>, linux-media@...r.kernel.org
Subject: [PATCH AUTOSEL 4.14 08/25] media: cobalt: fix race condition in setting HPD

From: Hans Verkuil <hverkuil-cisco@...all.nl>

[ Upstream commit 3d37ef41bed0854805ab9af22c422267510e1344 ]

The cobalt_s_bit_sysctrl reads the old register value over PCI,
then changes a bit and sets writes the new value to the register.

This is used among other things for setting the HPD output pin.

But if the HPD is changed for multiple inputs at the same time,
then this causes a race condition where a stale value is read.

Serialize this function with a mutex.

Signed-off-by: Hans Verkuil <hverkuil-cisco@...all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/media/pci/cobalt/cobalt-driver.c | 1 +
 drivers/media/pci/cobalt/cobalt-driver.h | 7 ++++++-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/media/pci/cobalt/cobalt-driver.c b/drivers/media/pci/cobalt/cobalt-driver.c
index 98b6cb9505d1..0c827f488317 100644
--- a/drivers/media/pci/cobalt/cobalt-driver.c
+++ b/drivers/media/pci/cobalt/cobalt-driver.c
@@ -687,6 +687,7 @@ static int cobalt_probe(struct pci_dev *pci_dev,
 		return -ENOMEM;
 	cobalt->pci_dev = pci_dev;
 	cobalt->instance = i;
+	mutex_init(&cobalt->pci_lock);
 
 	retval = v4l2_device_register(&pci_dev->dev, &cobalt->v4l2_dev);
 	if (retval) {
diff --git a/drivers/media/pci/cobalt/cobalt-driver.h b/drivers/media/pci/cobalt/cobalt-driver.h
index 00f773ec359a..9f8db7eaa43c 100644
--- a/drivers/media/pci/cobalt/cobalt-driver.h
+++ b/drivers/media/pci/cobalt/cobalt-driver.h
@@ -262,6 +262,8 @@ struct cobalt {
 	int instance;
 	struct pci_dev *pci_dev;
 	struct v4l2_device v4l2_dev;
+	/* serialize PCI access in cobalt_s_bit_sysctrl() */
+	struct mutex pci_lock;
 
 	void __iomem *bar0, *bar1;
 
@@ -331,10 +333,13 @@ static inline u32 cobalt_g_sysctrl(struct cobalt *cobalt)
 static inline void cobalt_s_bit_sysctrl(struct cobalt *cobalt,
 					int bit, int val)
 {
-	u32 ctrl = cobalt_read_bar1(cobalt, COBALT_SYS_CTRL_BASE);
+	u32 ctrl;
 
+	mutex_lock(&cobalt->pci_lock);
+	ctrl = cobalt_read_bar1(cobalt, COBALT_SYS_CTRL_BASE);
 	cobalt_write_bar1(cobalt, COBALT_SYS_CTRL_BASE,
 			(ctrl & ~(1UL << bit)) | (val << bit));
+	mutex_unlock(&cobalt->pci_lock);
 }
 
 static inline u32 cobalt_g_sysstat(struct cobalt *cobalt)
-- 
2.30.2