On 07/05/2017 10:50 PM, Cong Wang wrote:
> 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>
> Cc: Sainath Grandhi <sainath.gran...@intel.com>
> Signed-off-by: Cong Wang <xiyou.wangc...@gmail.com>
Tested-by: Christian Borntraeger <borntrae...@de.ibm.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 4d4173d..d88ae3c 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();
> @@ -1227,7 +1227,7 @@ 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;
>
