This is a note to let you know that I've just added the patch titled tap: convert a mutex to a spinlock to the 4.12-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: tap-convert-a-mutex-to-a-spinlock.patch and it can be found in the queue-4.12 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From foo@baz Mon Jul 17 18:46:41 CEST 2017 From: WANG Cong <xiyou.wangcong@xxxxxxxxx> Date: Mon, 10 Jul 2017 10:05:50 -0700 Subject: tap: convert a mutex to a spinlock 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; Patches currently in stable-queue which might be from xiyou.wangcong@xxxxxxxxx are queue-4.12/tap-convert-a-mutex-to-a-spinlock.patch