[PATCH] w1: Introduce a slave mutex for serializing IO.

[NeilBrown <neilb@suse.de>]

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w1 devices need a mutex to serial IO.
Most use master->mutex.

However that is used for other purposes and they can conflict.

In particular master->mutex is held while w1_attach_slave_device is
called.

For bq27000, this registers a 'powersupply' device which tries to
read the current status.  The attempt to read will cause a deadlock on
master->mutex.

So create a new per-slave mutex and use that for serializing IO for
bq27000.

Signed-off-by: NeilBrown <neilb@suse.de>
---
 drivers/w1/slaves/w1_bq27000.c |    4 ++--
 drivers/w1/w1.c                |    1 +
 drivers/w1/w1.h                |    1 +
 3 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/w1/slaves/w1_bq27000.c b/drivers/w1/slaves/w1_bq27000.c
index 52ad812..8755478 100644
--- a/drivers/w1/slaves/w1_bq27000.c
+++ b/drivers/w1/slaves/w1_bq27000.c
@@ -31,10 +31,10 @@ static int w1_bq27000_read(struct device *dev, unsigned int reg)
 	u8 val;
 	struct w1_slave *sl = container_of(dev->parent, struct w1_slave, dev);
 
-	mutex_lock(&sl->master->mutex);
+	mutex_lock(&sl->mutex);
 	w1_write_8(sl->master, HDQ_CMD_READ | reg);
 	val = w1_read_8(sl->master);
-	mutex_unlock(&sl->master->mutex);
+	mutex_unlock(&sl->mutex);
 
 	return val;
 }
diff --git a/drivers/w1/w1.c b/drivers/w1/w1.c
index 9761950..2173f83 100644
--- a/drivers/w1/w1.c
+++ b/drivers/w1/w1.c
@@ -688,6 +688,7 @@ static int w1_attach_slave_device(struct w1_master *dev, struct w1_reg_num *rn)
 	memcpy(&sl->reg_num, rn, sizeof(sl->reg_num));
 	atomic_set(&sl->refcnt, 0);
 	init_completion(&sl->released);
+	mutex_init(&sl->mutex);
 
 	spin_lock(&w1_flock);
 	f = w1_family_registered(rn->family);
diff --git a/drivers/w1/w1.h b/drivers/w1/w1.h
index 4d012ca..8c8be38 100644
--- a/drivers/w1/w1.h
+++ b/drivers/w1/w1.h
@@ -75,6 +75,7 @@ struct w1_slave
 	void			*family_data;
 	struct device		dev;
 	struct completion	released;
+	struct mutex		mutex;
 };
 
 typedef void (*w1_slave_found_callback)(struct w1_master *, u64);
-- 
1.7.10


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