[PATCH v2] w1: keep balance of mutex locks and refcnts

[Alexey Khoroshilov]

w1_therm_eeprom() and w1_DS18B20_precision() decrement THERM_REFCNT
on error paths, while they did not increment it yet.

read_therm() unlocks bus mutex on some error paths,
while it is not acquired.

The patch makes sure all the functions keep the balance in usage of
the mutex and the THERM_REFCNT.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@xxxxxxxxx>
---
v2: Implement suggestions of Evgeniy Polyakov.
Make use single exit point and not a mix of returns in the body of the function.
Switch to nested locking: grab the reference earlier and then try to lock the bus.

 drivers/w1/slaves/w1_therm.c | 59 +++++++++++++++++++++++---------------------
 1 file changed, 31 insertions(+), 28 deletions(-)

diff --git a/drivers/w1/slaves/w1_therm.c b/drivers/w1/slaves/w1_therm.c
index 259525c3382a..3c350dfbcd0b 100644
--- a/drivers/w1/slaves/w1_therm.c
+++ b/drivers/w1/slaves/w1_therm.c
@@ -268,17 +268,18 @@ static inline int w1_therm_eeprom(struct device *device)
 	int ret, max_trying = 10;
 	u8 *family_data = sl->family_data;
 
-	ret = mutex_lock_interruptible(&dev->bus_mutex);
-	if (ret != 0)
-		goto post_unlock;
-
 	if (!sl->family_data) {
 		ret = -ENODEV;
-		goto pre_unlock;
+		goto error;
 	}
 
 	/* prevent the slave from going away in sleep */
 	atomic_inc(THERM_REFCNT(family_data));
+
+	ret = mutex_lock_interruptible(&dev->bus_mutex);
+	if (ret != 0)
+		goto dec_refcnt;
+
 	memset(rom, 0, sizeof(rom));
 
 	while (max_trying--) {
@@ -306,17 +307,17 @@ static inline int w1_therm_eeprom(struct device *device)
 				sleep_rem = msleep_interruptible(tm);
 				if (sleep_rem != 0) {
 					ret = -EINTR;
-					goto post_unlock;
+					goto dec_refcnt;
 				}
 
 				ret = mutex_lock_interruptible(&dev->bus_mutex);
 				if (ret != 0)
-					goto post_unlock;
+					goto dec_refcnt;
 			} else if (!w1_strong_pullup) {
 				sleep_rem = msleep_interruptible(tm);
 				if (sleep_rem != 0) {
 					ret = -EINTR;
-					goto pre_unlock;
+					goto mt_unlock;
 				}
 			}
 
@@ -324,11 +325,11 @@ static inline int w1_therm_eeprom(struct device *device)
 		}
 	}
 
-pre_unlock:
+mt_unlock:
 	mutex_unlock(&dev->bus_mutex);
-
-post_unlock:
+dec_refcnt:
 	atomic_dec(THERM_REFCNT(family_data));
+error:
 	return ret;
 }
 
@@ -350,20 +351,22 @@ static inline int w1_DS18B20_precision(struct device *device, int val)
 
 	if (val > 12 || val < 9) {
 		pr_warn("Unsupported precision\n");
-		return -1;
+		ret = -EINVAL;
+		goto error;
 	}
 
-	ret = mutex_lock_interruptible(&dev->bus_mutex);
-	if (ret != 0)
-		goto post_unlock;
-
 	if (!sl->family_data) {
 		ret = -ENODEV;
-		goto pre_unlock;
+		goto error;
 	}
 
 	/* prevent the slave from going away in sleep */
 	atomic_inc(THERM_REFCNT(family_data));
+
+	ret = mutex_lock_interruptible(&dev->bus_mutex);
+	if (ret != 0)
+		goto dec_refcnt;
+
 	memset(rom, 0, sizeof(rom));
 
 	/* translate precision to bitmask (see datasheet page 9) */
@@ -411,11 +414,10 @@ static inline int w1_DS18B20_precision(struct device *device, int val)
 		}
 	}
 
-pre_unlock:
 	mutex_unlock(&dev->bus_mutex);
-
-post_unlock:
+dec_refcnt:
 	atomic_dec(THERM_REFCNT(family_data));
+error:
 	return ret;
 }
 
@@ -490,17 +492,18 @@ static ssize_t read_therm(struct device *device,
 	int ret, max_trying = 10;
 	u8 *family_data = sl->family_data;
 
-	ret = mutex_lock_interruptible(&dev->bus_mutex);
-	if (ret != 0)
-		goto error;
-
 	if (!family_data) {
 		ret = -ENODEV;
-		goto mt_unlock;
+		goto error;
 	}
 
 	/* prevent the slave from going away in sleep */
 	atomic_inc(THERM_REFCNT(family_data));
+
+	ret = mutex_lock_interruptible(&dev->bus_mutex);
+	if (ret != 0)
+		goto dec_refcnt;
+
 	memset(info->rom, 0, sizeof(info->rom));
 
 	while (max_trying--) {
@@ -542,7 +545,7 @@ static ssize_t read_therm(struct device *device,
 				sleep_rem = msleep_interruptible(tm);
 				if (sleep_rem != 0) {
 					ret = -EINTR;
-					goto dec_refcnt;
+					goto mt_unlock;
 				}
 			}
 
@@ -567,10 +570,10 @@ static ssize_t read_therm(struct device *device,
 			break;
 	}
 
-dec_refcnt:
-	atomic_dec(THERM_REFCNT(family_data));
 mt_unlock:
 	mutex_unlock(&dev->bus_mutex);
+dec_refcnt:
+	atomic_dec(THERM_REFCNT(family_data));
 error:
 	return ret;
 }
-- 
2.7.4