xfs: lockdep annotations for xfs_dqlock2

xfs_dqlock2 locks two xfs_dquots, which is fine as it always locks the
dquot with the lower id first.  Use mutex_lock_nested to tell lockdep
about this fact.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <david@fromorbit.com>

2 files changed, 24 insertions, 10 deletions

diff --git a/fs/xfs/quota/xfs_dquot.c b/fs/xfs/quota/xfs_dquot.c
index d68b4e1cf1d1..ebdf3c842dce 100644
--- a/fs/xfs/quota/xfs_dquot.c
+++ b/fs/xfs/quota/xfs_dquot.c
@@ -1383,6 +1383,12 @@ xfs_dqunlock_nonotify(
         mutex_unlock(&(dqp->q_qlock));
 }
 
+/*
+ * Lock two xfs_dquot structures.
+ *
+ * To avoid deadlocks we always lock the quota structure with
+ * the lowerd id first.
+ */
 void
 xfs_dqlock2(
         xfs_dquot_t     *d1,
@@ -1392,18 +1398,16 @@ xfs_dqlock2(
                 ASSERT(d1 != d2);
                 if (be32_to_cpu(d1->q_core.d_id) >
                     be32_to_cpu(d2->q_core.d_id)) {
-                        xfs_dqlock(d2);
-                        xfs_dqlock(d1);
+                        mutex_lock(&d2->q_qlock);
+                        mutex_lock_nested(&d1->q_qlock, XFS_QLOCK_NESTED);
                 } else {
-                        xfs_dqlock(d1);
-                        xfs_dqlock(d2);
-                }
-        } else {
-                if (d1) {
-                        xfs_dqlock(d1);
-                } else if (d2) {
-                        xfs_dqlock(d2);
+                        mutex_lock(&d1->q_qlock);
+                        mutex_lock_nested(&d2->q_qlock, XFS_QLOCK_NESTED);
                 }
+        } else if (d1) {
+                mutex_lock(&d1->q_qlock);
+        } else if (d2) {
+                mutex_lock(&d2->q_qlock);
         }
 }
 
diff --git a/fs/xfs/quota/xfs_dquot.h b/fs/xfs/quota/xfs_dquot.h
index 7e455337e2ba..d443e93b4331 100644
--- a/fs/xfs/quota/xfs_dquot.h
+++ b/fs/xfs/quota/xfs_dquot.h
@@ -97,6 +97,16 @@ typedef struct xfs_dquot {
 #define dq_hashlist     q_lists.dqm_hashlist
 #define dq_flags        q_lists.dqm_flags
 
+/*
+ * Lock hierachy for q_qlock:
+ *      XFS_QLOCK_NORMAL is the implicit default,
+ *      XFS_QLOCK_NESTED is the dquot with the higher id in xfs_dqlock2
+ */
+enum {
+        XFS_QLOCK_NORMAL = 0,
+        XFS_QLOCK_NESTED,
+};
+
 #define XFS_DQHOLD(dqp)         ((dqp)->q_nrefs++)
 
 #ifdef DEBUG