[RESEND PATCH net] tap: convert a mutex to a spinlock

[Cong Wang]

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 <borntrae...@de.ibm.com>
Tested-by: Christian Borntraeger <borntrae...@de.ibm.com>
Cc: Sainath Grandhi <sainath.gran...@intel.com>
Signed-off-by: Cong Wang <xiyou.wangc...@gmail.com>
---
 drivers/net/tap.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/drivers/net/tap.c b/drivers/net/tap.c
index 9af3239..3570c75 100644
--- 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 tap_dev *tap)
                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 tap_dev *tap)
                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_file(int major, int 
minor)
                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();
@@ -1244,7 +1244,7 @@ static int tap_list_add(dev_t major, const char 
*device_name)
        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;
 
-- 
2.5.5