mei: remove support for broken parallel read

commit cb97fbbcac15982406e0c74cd5512a8b6fcf10b3 upstream.

Parallel reads from multiple threads on a file descriptor
are not well defined and racy. It is safer to return to original
behavior and simply fail the additional read.
The solution is to remove request for next read credit.

Fixes: ff1586a7ea57 ("mei: enqueue consecutive reads")
Signed-off-by: Alexander Usyskin <alexander.usyskin@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/misc/mei/main.c b/drivers/misc/mei/main.c
index fa50635512e88985328849e216923785316ef79e..41f318631c6d808ee8f3e85ffd4c76c52d9e2368 100644 (file)
--- a/drivers/misc/mei/main.c
+++ b/drivers/misc/mei/main.c
@@ -182,32 +182,36 @@ static ssize_t mei_read(struct file *file, char __user *ubuf,
                goto out;
        }
 
-       if (rets == -EBUSY &&
-           !mei_cl_enqueue_ctrl_wr_cb(cl, length, MEI_FOP_READ, file)) {
-               rets = -ENOMEM;
-               goto out;
-       }
 
-       do {
-               mutex_unlock(&dev->device_lock);
-
-               if (wait_event_interruptible(cl->rx_wait,
-                                            (!list_empty(&cl->rd_completed)) ||
-                                            (!mei_cl_is_connected(cl)))) {
+again:
+       mutex_unlock(&dev->device_lock);
+       if (wait_event_interruptible(cl->rx_wait,
+                                    !list_empty(&cl->rd_completed) ||
+                                    !mei_cl_is_connected(cl))) {
+               if (signal_pending(current))
+                       return -EINTR;
+               return -ERESTARTSYS;
+       }
+       mutex_lock(&dev->device_lock);
 
-                       if (signal_pending(current))
-                               return -EINTR;
-                       return -ERESTARTSYS;
-               }
+       if (!mei_cl_is_connected(cl)) {
+               rets = -ENODEV;
+               goto out;
+       }
 
-               mutex_lock(&dev->device_lock);
-               if (!mei_cl_is_connected(cl)) {
-                       rets = -ENODEV;
-                       goto out;
-               }
+       cb = mei_cl_read_cb(cl, file);
+       if (!cb) {
+               /*
+                * For amthif all the waiters are woken up,
+                * but only fp with matching cb->fp get the cb,
+                * the others have to return to wait on read.
+                */
+               if (cl == &dev->iamthif_cl)
+                       goto again;
 
-               cb = mei_cl_read_cb(cl, file);
-       } while (!cb);
+               rets = 0;
+               goto out;
+       }
 
 copy_buffer:
        /* now copy the data to user space */