ieee1394: dv1394: fix possible deadlock in multithreaded clients

[firefly-linux-kernel-4.4.55.git] / drivers / ieee1394 / dv1394.c

diff --git a/drivers/ieee1394/dv1394.c b/drivers/ieee1394/dv1394.c
index df70f51279d85db8d21b1731c9d7b3b96ca8e668..53329972c7dba580df1b8bd830c8cf8a85545b47 100644 (file)
--- a/drivers/ieee1394/dv1394.c
+++ b/drivers/ieee1394/dv1394.c
@@ -1270,8 +1270,14 @@ static int dv1394_mmap(struct file *file, struct vm_area_struct *vma)
        struct video_card *video = file_to_video_card(file);
        int retval = -EINVAL;
 
-       /* serialize mmap */
-       mutex_lock(&video->mtx);
+       /*
+        * We cannot use the blocking variant mutex_lock here because .mmap
+        * is called with mmap_sem held, while .ioctl, .read, .write acquire
+        * video->mtx and subsequently call copy_to/from_user which will
+        * grab mmap_sem in case of a page fault.
+        */
+       if (!mutex_trylock(&video->mtx))
+               return -EAGAIN;
 
        if ( ! video_card_initialized(video) ) {
                retval = do_dv1394_init_default(video);