4.4-stable review patch. If anyone has any objections, please let me know.
------------------
[ Upstream commit 4c127fd16e6b33ecb7badc091480c84ea9aebeb6 ]
Right now, if stm device removal has to unbind from a policy (that is, an stm device that has STP policy, gets removed), it will trigger a nested lock on the stm device's policy mutex.
This patch fixes the problem by moving the locking from the policy unbinding to policy removal (configfs path), where it's actually needed; the other caller of the policy unbinding function already takes the mutex around the call.
Signed-off-by: Alexander Shishkin alexander.shishkin@linux.intel.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/hwtracing/stm/policy.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-)
diff --git a/drivers/hwtracing/stm/policy.c b/drivers/hwtracing/stm/policy.c index 11ab6d01adf6..94d3abfb737a 100644 --- a/drivers/hwtracing/stm/policy.c +++ b/drivers/hwtracing/stm/policy.c @@ -272,13 +272,17 @@ void stp_policy_unbind(struct stp_policy *policy) { struct stm_device *stm = policy->stm;
+ /* + * stp_policy_release() will not call here if the policy is already + * unbound; other users should not either, as no link exists between + * this policy and anything else in that case + */ if (WARN_ON_ONCE(!policy->stm)) return;
- mutex_lock(&stm->policy_mutex); - stm->policy = NULL; - mutex_unlock(&stm->policy_mutex); + lockdep_assert_held(&stm->policy_mutex);
+ stm->policy = NULL; policy->stm = NULL;
stm_put_device(stm); @@ -287,8 +291,16 @@ void stp_policy_unbind(struct stp_policy *policy) static void stp_policy_release(struct config_item *item) { struct stp_policy *policy = to_stp_policy(item); + struct stm_device *stm = policy->stm;
+ /* a policy *can* be unbound and still exist in configfs tree */ + if (!stm) + return; + + mutex_lock(&stm->policy_mutex); stp_policy_unbind(policy); + mutex_unlock(&stm->policy_mutex); + kfree(policy); }