dmaengine: move channel device_node deletion to driver

Channel device_node deletion is managed by the device driver rather than
the dmaengine core. The deletion was accidentally introduced when making
channel unregister dynamic. It causes xilinx_dma module to crash on unload
as reported by Radhey. Remove chan->device_node delete in dmaengine and
also fix up idxd driver.

[   42.142705] Internal error: Oops: 96000044 [#1] SMP
[   42.147566] Modules linked in: xilinx_dma(-) clk_xlnx_clock_wizard uio_pdrv_genirq
[   42.155139] CPU: 1 PID: 2075 Comm: rmmod Not tainted 5.10.1-00026-g3a2e6dd7a05-dirty #192
[   42.163302] Hardware name: Enclustra XU5 SOM (DT)
[   42.167992] pstate: 40000005 (nZcv daif -PAN -UAO -TCO BTYPE=--)
[   42.173996] pc : xilinx_dma_chan_remove+0x74/0xa0 [xilinx_dma]
[   42.179815] lr : xilinx_dma_chan_remove+0x70/0xa0 [xilinx_dma]
[   42.185636] sp : ffffffc01112bca0
[   42.188935] x29: ffffffc01112bca0 x28: ffffff80402ea640

xilinx_dma_chan_remove+0x74/0xa0:
__list_del at ./include/linux/list.h:112 (inlined by)
__list_del_entry at./include/linux/list.h:135 (inlined by)
list_del at ./include/linux/list.h:146 (inlined by)
xilinx_dma_chan_remove at drivers/dma/xilinx/xilinx_dma.c:2546

Fixes: e81274cd6b ("dmaengine: add support to dynamic register/unregister of channels")
Reported-by: Radhey Shyam Pandey <radheys@xilinx.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Tested-by: Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>
Link: https://lore.kernel.org/r/161099092469.2495902.5064826526660062342.stgit@djiang5-desk3.ch.intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Cc: stable@vger.kernel.org # 5.9+

drivers/dma/dmaengine.c

@@ -1110,7 +1110,6 @@ static void __dma_async_device_channel_unregister(struct dma_device *device,
 		  "%s called while %d clients hold a reference\n",
 		  __func__, chan->client_count);
 	mutex_lock(&dma_list_mutex);
-	list_del(&chan->device_node);
 	device->chancnt--;
 	chan->dev->chan = NULL;
 	mutex_unlock(&dma_list_mutex);

drivers/dma/idxd/dma.c

@@ -205,5 +205,8 @@ int idxd_register_dma_channel(struct idxd_wq *wq)
 
 void idxd_unregister_dma_channel(struct idxd_wq *wq)
 {
-	dma_async_device_channel_unregister(&wq->idxd->dma_dev, &wq->dma_chan);
+	struct dma_chan *chan = &wq->dma_chan;
+
+	dma_async_device_channel_unregister(&wq->idxd->dma_dev, chan);
+	list_del(&chan->device_node);
 }