Unlocking a mutex twice is wrong. Hence modify blkcg_policy_register()
such that blkcg_pol_mutex is unlocked once if cpd == NULL. This patch
avoids that smatch reports the following error:

block/blk-cgroup.c:1378: blkcg_policy_register() error: double unlock 
'mutex:&blkcg_pol_mutex'

Signed-off-by: Bart Van Assche <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: <[email protected]>
---
 block/blk-cgroup.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index dd38e5c..cdbca1c 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1327,8 +1327,10 @@ int blkcg_policy_register(struct blkcg_policy *pol)
        for (i = 0; i < BLKCG_MAX_POLS; i++)
                if (!blkcg_policy[i])
                        break;
-       if (i >= BLKCG_MAX_POLS)
+       if (i >= BLKCG_MAX_POLS) {
+               mutex_unlock(&blkcg_pol_mutex);
                goto err_unlock;
+       }
 
        /* register @pol */
        pol->plid = i;
@@ -1374,8 +1376,8 @@ err_free_cpds:
                }
        }
        blkcg_policy[pol->plid] = NULL;
+
 err_unlock:
-       mutex_unlock(&blkcg_pol_mutex);
        mutex_unlock(&blkcg_pol_register_mutex);
        return ret;
 }
-- 
2.10.0

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