1 files changed, 14 insertions, 4 deletions

diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index 4a5863b79de9..fa053151fa96 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -421,6 +421,16 @@ static int kernfs_file_mmap(struct file *file, struct vm_area_struct *vma)
         const struct kernfs_ops *ops;
         int rc;
 
+        /*
+         * mmap path and of->mutex are prone to triggering spurious lockdep
+         * warnings and we don't want to add spurious locking dependency
+         * between the two.  Check whether mmap is actually implemented
+         * without grabbing @of->mutex by testing HAS_MMAP flag.  See the
+         * comment in kernfs_file_open() for more details.
+         */
+        if (!(of->sd->s_flags & SYSFS_FLAG_HAS_MMAP))
+                return -ENODEV;
+
         mutex_lock(&of->mutex);
 
         rc = -ENODEV;
@@ -428,10 +438,7 @@ static int kernfs_file_mmap(struct file *file, struct vm_area_struct *vma)
                 goto out_unlock;
 
         ops = kernfs_ops(of->sd);
-        if (ops->mmap)
-                rc = ops->mmap(of, vma);
-        if (rc)
-                goto out_put;
+        rc = ops->mmap(of, vma);
 
         /*
          * PowerPC's pci_mmap of legacy_mem uses shmem_zero_setup()
@@ -596,6 +603,9 @@ static int kernfs_file_open(struct inode *inode, struct file *file)
          * happen on the same file.  At this point, we can't easily give
          * each file a separate locking class.  Let's differentiate on
          * whether the file has mmap or not for now.
+         *
+         * Both paths of the branch look the same.  They're supposed to
+         * look that way and give @of->mutex different static lockdep keys.
          */
         if (has_mmap)
                 mutex_init(&of->mutex);