[PATCH 4.12 16/84] tap: convert a mutex to a spinlock

From: Greg Kroah-Hartman
Date: Wed Jul 19 2017 - 06:04:57 EST


4.12-stable review patch. If anyone has any objections, please let me know.

------------------

From: WANG Cong <xiyou.wangcong@xxxxxxxxx>


[ Upstream commit ffa423fb3251f8737303ffc3b0659e86e501808e ]

We are not allowed to block on the RCU reader side, so can't
just hold the mutex as before. As a quick fix, convert it to
a spinlock.

Fixes: d9f1f61c0801 ("tap: Extending tap device create/destroy APIs")
Reported-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
Tested-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
Cc: Sainath Grandhi <sainath.grandhi@xxxxxxxxx>
Signed-off-by: Cong Wang <xiyou.wangcong@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/net/tap.c | 18 +++++++++---------
1 file changed, 9 insertions(+), 9 deletions(-)

--- a/drivers/net/tap.c
+++ b/drivers/net/tap.c
@@ -106,7 +106,7 @@ struct major_info {
struct rcu_head rcu;
dev_t major;
struct idr minor_idr;
- struct mutex minor_lock;
+ spinlock_t minor_lock;
const char *device_name;
struct list_head next;
};
@@ -416,15 +416,15 @@ int tap_get_minor(dev_t major, struct ta
goto unlock;
}

- mutex_lock(&tap_major->minor_lock);
- retval = idr_alloc(&tap_major->minor_idr, tap, 1, TAP_NUM_DEVS, GFP_KERNEL);
+ spin_lock(&tap_major->minor_lock);
+ retval = idr_alloc(&tap_major->minor_idr, tap, 1, TAP_NUM_DEVS, GFP_ATOMIC);
if (retval >= 0) {
tap->minor = retval;
} else if (retval == -ENOSPC) {
netdev_err(tap->dev, "Too many tap devices\n");
retval = -EINVAL;
}
- mutex_unlock(&tap_major->minor_lock);
+ spin_unlock(&tap_major->minor_lock);

unlock:
rcu_read_unlock();
@@ -442,12 +442,12 @@ void tap_free_minor(dev_t major, struct
goto unlock;
}

- mutex_lock(&tap_major->minor_lock);
+ spin_lock(&tap_major->minor_lock);
if (tap->minor) {
idr_remove(&tap_major->minor_idr, tap->minor);
tap->minor = 0;
}
- mutex_unlock(&tap_major->minor_lock);
+ spin_unlock(&tap_major->minor_lock);

unlock:
rcu_read_unlock();
@@ -467,13 +467,13 @@ static struct tap_dev *dev_get_by_tap_fi
goto unlock;
}

- mutex_lock(&tap_major->minor_lock);
+ spin_lock(&tap_major->minor_lock);
tap = idr_find(&tap_major->minor_idr, minor);
if (tap) {
dev = tap->dev;
dev_hold(dev);
}
- mutex_unlock(&tap_major->minor_lock);
+ spin_unlock(&tap_major->minor_lock);

unlock:
rcu_read_unlock();
@@ -1227,7 +1227,7 @@ static int tap_list_add(dev_t major, con
tap_major->major = MAJOR(major);

idr_init(&tap_major->minor_idr);
- mutex_init(&tap_major->minor_lock);
+ spin_lock_init(&tap_major->minor_lock);

tap_major->device_name = device_name;