w1: introduce a slave mutex for serializing IO

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>
Cc: Evgeniy Polyakov <zbr@ioremap.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

3 files changed, 4 insertions, 2 deletions

diff --git a/drivers/w1/slaves/w1_bq27000.c b/drivers/w1/slaves/w1_bq27000.c
index 52ad812fa1e7..87554788fa32 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 2f2e894ea0c8..69075c3dfc73 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 4d012ca3f32c..8c8be380a98a 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);