From: Mr NeilBrown <neilb@suse.de>
Date: Thu, 2 Jul 2020 21:43:45 +0000 (+1000)
Subject: LU-9679 lov: annotate nested locking of obd_dev_mutex
X-Git-Tag: 2.13.55~19
X-Git-Url: https://git.whamcloud.com/?p=fs%2Flustre-release.git;a=commitdiff_plain;h=10dae4c3b68ebc2509d7089037eccc9f4460c08f

LU-9679 lov: annotate nested locking of obd_dev_mutex

obd_statfs() can call lmv_statfs() with ->obd_dev_mutex helds.
lmv_statfs will then call obd_statfs() on a different device
and ->obd_dev_mutex will be taken again.  This is a *different*
mutex, but lockdep cannot see the difference, so it complains.

We can tell lockdep not to worry in this case using
mutex_lock_interruptible_nested().

Test-Parameters: trivial
Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: I0776407b722dd29ab1321289953b63f76fce7ceb
Reviewed-on: https://review.whamcloud.com/39248
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
---

diff --git a/lustre/include/obd_class.h b/lustre/include/obd_class.h
index 2b2f2fa..d624c27 100644
--- a/lustre/include/obd_class.h
+++ b/lustre/include/obd_class.h
@@ -41,13 +41,17 @@
 #include <uapi/linux/lustre/lustre_idl.h>
 #include <lprocfs_status.h>
 
-#define OBD_STATFS_NODELAY      0x0001  /* requests should be send without delay
-                                         * and resends for avoid deadlocks */
-#define OBD_STATFS_FROM_CACHE   0x0002  /* the statfs callback should not update
-                                         * obd_osfs_age */
+#define OBD_STATFS_NODELAY	0x0001	/* requests should be send without delay
+					 * and resends for avoid deadlocks */
+#define OBD_STATFS_FROM_CACHE	0x0002	/* the statfs callback should not update
+					 * obd_osfs_age */
 #define OBD_STATFS_FOR_MDT0	0x0004	/* The statfs is only for retrieving
 					 * information from MDT0. */
 #define OBD_STATFS_SUM		0x0008	/* get aggregated statfs from MDT */
+#define OBD_STATFS_NESTED	0x0010	/* Call while already holding
+					 * obd_dev_mutex of a difference
+					 * device.
+					 */
 
 extern rwlock_t obd_dev_lock;
 
@@ -1063,7 +1067,9 @@ static inline int obd_statfs(const struct lu_env *env, struct obd_export *exp,
 	    ((obd->obd_osfs.os_state & OS_STATFS_SUM) &&
 	     !(flags & OBD_STATFS_SUM))) {
 		/* the RPC will block anyway, so avoid sending many at once */
-		rc = mutex_lock_interruptible(&obd->obd_dev_mutex);
+		rc = mutex_lock_interruptible_nested(&obd->obd_dev_mutex,
+						     (flags & OBD_STATFS_NESTED)
+						     ? SINGLE_DEPTH_NESTING : 0);
 		if (rc)
 			RETURN(rc);
 		if (obd->obd_osfs_age < max_age ||
diff --git a/lustre/lmv/lmv_obd.c b/lustre/lmv/lmv_obd.c
index 1f470b3..9c4da99 100644
--- a/lustre/lmv/lmv_obd.c
+++ b/lustre/lmv/lmv_obd.c
@@ -1256,7 +1256,8 @@ static int lmv_statfs(const struct lu_env *env, struct obd_export *exp,
 		if (!tgt || !tgt->ltd_exp)
 			continue;
 
-		rc = obd_statfs(env, tgt->ltd_exp, temp, max_age, flags);
+		rc = obd_statfs(env, tgt->ltd_exp, temp, max_age,
+				flags | OBD_STATFS_NESTED);
 		if (rc) {
 			CERROR("%s: can't stat MDS #%d: rc = %d\n",
 			       tgt->ltd_exp->exp_obd->obd_name, i, rc);