habanalabs: all FD must be closed before removing device

This patch fixes a bug in the implementation of the function that removes
the device.

The bug can happen when the device is removed but not the driver itself
(e.g. remove by the OS due to PCI freeze in Power architecture).

In that case, there maybe open users that are calling IOCTLs while the
device is removed. This is a possible race condition that the driver must
handle. Otherwise, a kernel panic may occur.

This race is prevented in the hard-reset flow, because the driver makes
sure the users are closed before continuing with the hard-reset. This
race can not occur when the driver itself is removed because the OS makes
sure all the file descriptors are closed.

The fix is to make sure the open users close their file descriptors and if
they don't (after a certain amount of time), the driver sends them a
SIGKILL, because the remove of the device can't be stopped.

The patch re-uses the same code that is called from the hard-reset flow.

Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>

drivers/misc/habanalabs/device.c

@@ -513,11 +513,8 @@ disable_device:
 	return rc;
 }
 
-static void hl_device_hard_reset_pending(struct work_struct *work)
+static void device_kill_open_processes(struct hl_device *hdev)
 {
-	struct hl_device_reset_work *device_reset_work =
-		container_of(work, struct hl_device_reset_work, reset_work);
-	struct hl_device *hdev = device_reset_work->hdev;
 	u16 pending_total, pending_cnt;
 	struct task_struct *task = NULL;
 
@@ -552,6 +549,12 @@ static void hl_device_hard_reset_pending(struct work_struct *work)
 		}
 	}
 
+	/* We killed the open users, but because the driver cleans up after the
+	 * user contexts are closed (e.g. mmu mappings), we need to wait again
+	 * to make sure the cleaning phase is finished before continuing with
+	 * the reset
+	 */
+
 	pending_cnt = pending_total;
 
 	while ((atomic_read(&hdev->fd_open_cnt)) && (pending_cnt)) {
@@ -567,6 +570,16 @@ static void hl_device_hard_reset_pending(struct work_struct *work)
 
 	mutex_unlock(&hdev->fd_open_cnt_lock);
 
+}
+
+static void device_hard_reset_pending(struct work_struct *work)
+{
+	struct hl_device_reset_work *device_reset_work =
+		container_of(work, struct hl_device_reset_work, reset_work);
+	struct hl_device *hdev = device_reset_work->hdev;
+
+	device_kill_open_processes(hdev);
+
 	hl_device_reset(hdev, true, true);
 
 	kfree(device_reset_work);
@@ -650,7 +663,7 @@ again:
 		 * from a dedicated work
 		 */
 		INIT_WORK(&device_reset_work->reset_work,
-				hl_device_hard_reset_pending);
+				device_hard_reset_pending);
 		device_reset_work->hdev = hdev;
 		schedule_work(&device_reset_work->reset_work);
 
@@ -1049,6 +1062,15 @@ void hl_device_fini(struct hl_device *hdev)
 	/* Mark device as disabled */
 	hdev->disabled = true;
 
+	/*
+	 * Flush anyone that is inside the critical section of enqueue
+	 * jobs to the H/W
+	 */
+	hdev->asic_funcs->hw_queues_lock(hdev);
+	hdev->asic_funcs->hw_queues_unlock(hdev);
+
+	device_kill_open_processes(hdev);
+
 	hl_hwmon_fini(hdev);
 
 	device_late_fini(hdev);