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patch "w1_therm reference count family data" added to char-misc-testing

PATCH [email protected] 1 participant 1 message May 24, 2015

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This is a note to let you know that I've just added the patch titled

w1_therm reference count family data

to my char-misc git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git
in the char-misc-testing branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will be merged to the char-misc-next branch sometime soon, after it passes testing, and the merge window is open.

If you have any questions about this process, please let me know.

Quoted 1 line

From f7134eea05b2fb4a2c0935f8a540539fff01f3eb Mon Sep 17 00:00:00 2001

From: David Fries <[email protected]>
Date: Fri, 8 May 2015 19:51:50 -0500
Subject: w1_therm reference count family data

A temperature conversion can take 750 ms and when possible the w1_therm slave driver drops the bus_mutex to allow other bus operations, but that includes operations such as a periodic slave search, which can remove this slave when it is no longer detected. If that happens the sl->family_data will be freed and set to NULL causing w1_slave_show to crash when it wakes up.

Signed-off-by David Fries <[email protected]>
Reported-By Thorsten Bschorr <[email protected]>
Tested-by Thorsten Bschorr <[email protected]>
Acked-by Evgeniy Polyakov <[email protected]>
Cc stable <[email protected]>
Signed-off-by Greg Kroah-Hartman <[email protected]>
---
 drivers/w1/slaves/w1_therm.c | 62 +++++++++++++++++++++++++++++++++-----------
 1 file changed, 47 insertions(+), 15 deletions(-)
drivers/w1/slaves/w1_therm.c +47 -15
index 1f11a20a8ab9..55eb86c9e214 100644
@@ -59,16 +59,32 @@ MODULE_ALIAS("w1-family-" __stringify(W1_THERM_DS28EA00));
 static int w1_strong_pullup = 1;
 module_param_named(strong_pullup, w1_strong_pullup, int, 0);
 
+struct w1_therm_family_data {
+	uint8_t rom[9];
+	atomic_t refcnt;
+};
+
+/* return the address of the refcnt in the family data */
+#define THERM_REFCNT(family_data) \
+	(&((struct w1_therm_family_data*)family_data)->refcnt)
+
 static int w1_therm_add_slave(struct w1_slave *sl)
 {
-	sl->family_data = kzalloc(9, GFP_KERNEL);
+	sl->family_data = kzalloc(sizeof(struct w1_therm_family_data),
+		GFP_KERNEL);
 	if (!sl->family_data)
 		return -ENOMEM;
+	atomic_set(THERM_REFCNT(sl->family_data), 1);
 	return 0;
 }
 
 static void w1_therm_remove_slave(struct w1_slave *sl)
 {
+	int refcnt = atomic_sub_return(1, THERM_REFCNT(sl->family_data));
+	while(refcnt) {
+		msleep(1000);
+		refcnt = atomic_read(THERM_REFCNT(sl->family_data));
+	}
 	kfree(sl->family_data);
 	sl->family_data = NULL;
 }

@@ -194,13 +210,22 @@ static ssize_t w1_slave_show(struct device *device,
 	struct w1_slave *sl = dev_to_w1_slave(device);
 	struct w1_master *dev = sl->master;
 	u8 rom[9], crc, verdict, external_power;
-	int i, max_trying = 10;
+	int i, ret, max_trying = 10;
 	ssize_t c = PAGE_SIZE;
+	u8 *family_data = sl->family_data;
+
+	ret = mutex_lock_interruptible(&dev->bus_mutex);
+	if (ret != 0)
+		goto post_unlock;
 
-	i = mutex_lock_interruptible(&dev->bus_mutex);
-	if (i != 0)
-		return i;
+	if(!sl->family_data)
+	{
+		ret = -ENODEV;
+		goto pre_unlock;
+	}
 
+	/* prevent the slave from going away in sleep */
+	atomic_inc(THERM_REFCNT(family_data));
 	memset(rom, 0, sizeof(rom));
 
 	while (max_trying--) {

@@ -230,17 +255,19 @@ static ssize_t w1_slave_show(struct device *device,
 				mutex_unlock(&dev->bus_mutex);
 
 				sleep_rem = msleep_interruptible(tm);
-				if (sleep_rem != 0)
-					return -EINTR;
+				if (sleep_rem != 0) {
+					ret = -EINTR;
+					goto post_unlock;
+				}
 
-				i = mutex_lock_interruptible(&dev->bus_mutex);
-				if (i != 0)
-					return i;
+				ret = mutex_lock_interruptible(&dev->bus_mutex);
+				if (ret != 0)
+					goto post_unlock;
 			} else if (!w1_strong_pullup) {
 				sleep_rem = msleep_interruptible(tm);
 				if (sleep_rem != 0) {
-					mutex_unlock(&dev->bus_mutex);
-					return -EINTR;
+					ret = -EINTR;
+					goto pre_unlock;
 				}
 			}
 

@@ -269,19 +296,24 @@ static ssize_t w1_slave_show(struct device *device,
 	c -= snprintf(buf + PAGE_SIZE - c, c, ": crc=%02x %s\n",
 			   crc, (verdict) ? "YES" : "NO");
 	if (verdict)
-		memcpy(sl->family_data, rom, sizeof(rom));
+		memcpy(family_data, rom, sizeof(rom));
 	else
 		dev_warn(device, "Read failed CRC check\n");
 
 	for (i = 0; i < 9; ++i)
 		c -= snprintf(buf + PAGE_SIZE - c, c, "%02x ",
-			      ((u8 *)sl->family_data)[i]);
+			      ((u8 *)family_data)[i]);
 
 	c -= snprintf(buf + PAGE_SIZE - c, c, "t=%d\n",
 		w1_convert_temp(rom, sl->family->fid));
+	ret = PAGE_SIZE - c;
+
+pre_unlock:
 	mutex_unlock(&dev->bus_mutex);
 
-	return PAGE_SIZE - c;
+post_unlock:
+	atomic_dec(THERM_REFCNT(family_data));
+	return ret;
 }
 
 static int __init w1_therm_init(void)
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