[PATCH] staging: lustre: fix lock imbalance

[PATCH] staging: lustre: fix lock imbalance

[Joshua Clayton]

nrs_resource_put_safe() might hold a lock one one struct
while operating on the other.
There are 2 levels of structures.
Use nrs_policy_put(), which has locking baked in.

sparse gives the following warning:
drivers/staging/lustre//lustre/ptlrpc/nrs.c:498:39:
warning: context imbalance in 'nrs_resource_put_safe' -
  different lock contexts for basic block
---
 drivers/staging/lustre/lustre/ptlrpc/nrs.c | 13 ++-----------
 1 file changed, 2 insertions(+), 11 deletions(-)

diff --git a/drivers/staging/lustre/lustre/ptlrpc/nrs.c b/drivers/staging/lustre/lustre/ptlrpc/nrs.c
index 7044e1f..9028b12 100644
--- a/drivers/staging/lustre/lustre/ptlrpc/nrs.c
+++ b/drivers/staging/lustre/lustre/ptlrpc/nrs.c
@@ -496,18 +496,9 @@ static void nrs_resource_put_safe(struct ptlrpc_nrs_resource **resp)
 	}
 
 	for (i = 0; i < NRS_RES_MAX; i++) {
-		if (pols[i] == NULL)
-			continue;
-
-		if (nrs == NULL) {
-			nrs = pols[i]->pol_nrs;
-			spin_lock(&nrs->nrs_lock);
-		}
-		nrs_policy_put_locked(pols[i]);
+		if (pols[i])
+			nrs_policy_put(pols[i]);
 	}
-
-	if (nrs != NULL)
-		spin_unlock(&nrs->nrs_lock);
 }
 
 /**
-- 
2.6.4

Re: [PATCH] staging: lustre: fix lock imbalance

[kbuild test robot]

[-- Attachment #1: Type: text/plain, Size: 2810 bytes --]

[if your patch is applied to the wrong git tree, please drop us a note to help improving the system]
Hi Joshua,

[auto build test WARNING on staging/staging-testing]
[also build test WARNING on v4.4-rc6 next-20151223]

url:    https://github.com/0day-ci/linux/commits/Joshua-Clayton/staging-lustre-fix-lock-imbalance/20151227-131137
config: x86_64-allyesconfig (attached as .config)
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

All warnings (new ones prefixed by >>):

   drivers/staging/lustre/lustre/ptlrpc/nrs.c: In function 'nrs_resource_put_safe':
>> drivers/staging/lustre/lustre/ptlrpc/nrs.c:485:21: warning: unused variable 'nrs' [-Wunused-variable]
     struct ptlrpc_nrs *nrs = NULL;
                        ^

vim +/nrs +485 drivers/staging/lustre/lustre/ptlrpc/nrs.c

d7e09d039 Peng Tao 2013-05-02  469  			nrs_policy_put(primary);
d7e09d039 Peng Tao 2013-05-02  470  	}
d7e09d039 Peng Tao 2013-05-02  471  }
d7e09d039 Peng Tao 2013-05-02  472  
d7e09d039 Peng Tao 2013-05-02  473  /**
d7e09d039 Peng Tao 2013-05-02  474   * Releases references to resource hierarchies and policies, because they are no
d7e09d039 Peng Tao 2013-05-02  475   * longer required; used when request handling has been completed, or the
d7e09d039 Peng Tao 2013-05-02  476   * request is moving to the high priority NRS head.
d7e09d039 Peng Tao 2013-05-02  477   *
d7e09d039 Peng Tao 2013-05-02  478   * \param resp	the resource hierarchy that is being released
d7e09d039 Peng Tao 2013-05-02  479   *
d7e09d039 Peng Tao 2013-05-02  480   * \see ptlrpc_nrs_req_finalize()
d7e09d039 Peng Tao 2013-05-02  481   */
d7e09d039 Peng Tao 2013-05-02  482  static void nrs_resource_put_safe(struct ptlrpc_nrs_resource **resp)
d7e09d039 Peng Tao 2013-05-02  483  {
d7e09d039 Peng Tao 2013-05-02  484  	struct ptlrpc_nrs_policy *pols[NRS_RES_MAX];
d7e09d039 Peng Tao 2013-05-02 @485  	struct ptlrpc_nrs *nrs = NULL;
d7e09d039 Peng Tao 2013-05-02  486  	int i;
d7e09d039 Peng Tao 2013-05-02  487  
d7e09d039 Peng Tao 2013-05-02  488  	for (i = 0; i < NRS_RES_MAX; i++) {
d7e09d039 Peng Tao 2013-05-02  489  		if (resp[i] != NULL) {
d7e09d039 Peng Tao 2013-05-02  490  			pols[i] = resp[i]->res_policy;
d7e09d039 Peng Tao 2013-05-02  491  			nrs_resource_put(resp[i]);
d7e09d039 Peng Tao 2013-05-02  492  			resp[i] = NULL;
d7e09d039 Peng Tao 2013-05-02  493  		} else {

:::::: The code at line 485 was first introduced by commit
:::::: d7e09d0397e84eefbabfd9cb353221f3c6448d83 staging: add Lustre file system client support

:::::: TO: Peng Tao <bergwolf@gmail.com>
:::::: CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

[-- Attachment #2: .config.gz --]
[-- Type: application/octet-stream, Size: 51410 bytes --]

[PATCH v2] staging: lustre: fix lock imbalance

[Joshua Clayton]

nrs_resource_put_safe() might hold a lock one one struct
while operating on the other.
There are 2 levels of structures.
Use nrs_policy_put(), which has locking baked in.

sparse gives the following warning:
drivers/staging/lustre//lustre/ptlrpc/nrs.c:498:39:
warning: context imbalance in 'nrs_resource_put_safe' -
  different lock contexts for basic block

Signed-off-by: Joshua Clayton <stillcompiling@gmail.com>
---
changed for v2:
- remove unused nrs variable

 drivers/staging/lustre/lustre/ptlrpc/nrs.c | 14 ++------------
 1 file changed, 2 insertions(+), 12 deletions(-)

diff --git a/drivers/staging/lustre/lustre/ptlrpc/nrs.c b/drivers/staging/lustre/lustre/ptlrpc/nrs.c
index 7044e1f..57acf8c 100644
--- a/drivers/staging/lustre/lustre/ptlrpc/nrs.c
+++ b/drivers/staging/lustre/lustre/ptlrpc/nrs.c
@@ -482,7 +482,6 @@ static void nrs_resource_get_safe(struct ptlrpc_nrs *nrs,
 static void nrs_resource_put_safe(struct ptlrpc_nrs_resource **resp)
 {
 	struct ptlrpc_nrs_policy *pols[NRS_RES_MAX];
-	struct ptlrpc_nrs *nrs = NULL;
 	int i;
 
 	for (i = 0; i < NRS_RES_MAX; i++) {
@@ -496,18 +495,9 @@ static void nrs_resource_put_safe(struct ptlrpc_nrs_resource **resp)
 	}
 
 	for (i = 0; i < NRS_RES_MAX; i++) {
-		if (pols[i] == NULL)
-			continue;
-
-		if (nrs == NULL) {
-			nrs = pols[i]->pol_nrs;
-			spin_lock(&nrs->nrs_lock);
-		}
-		nrs_policy_put_locked(pols[i]);
+		if (pols[i])
+			nrs_policy_put(pols[i]);
 	}
-
-	if (nrs != NULL)
-		spin_unlock(&nrs->nrs_lock);
 }
 
 /**
-- 
2.6.4