Hi Dave,
I have a query on below patch (commit-e81274cd6b52). It causes regression
in xilinx_dma driver and there is a reported kernel crash on rmmod.
commit e81274cd6b5264809384066e09a5253708822522
Author: Dave Jiang <dave.jiang@xxxxxxxxx>
Date: Tue Jan 21 16:43:53 2020 -0700
dmaengine: add support to dynamic register/unregister of channels
With the channel registration routines broken out, now add support code to
allow independent registering and unregistering of channels in a hotplug
fashion.
Crash on the unloading xilinx_dma module is reproducible after e81274cd6b526
mainline commit is added in the 5.6 kernel.
[ 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
Looking into e81274cd6b526 commit - It deletes channel device_node entry.
Same channel device_node entry is also deleted in
xilinx_dma_chan_remove as a result we see this crash.
@@ -993,12 +1007,22 @@ 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--;
I want to know some background for this change. In dmaengine driver -
we are adding channel device node entry so deleting it in the exit
the path should be done in dmaengine driver and not in _channel_unregister?
NOTE: This issue is reported in https://www.spinics.net/lists/dmaengine/msg24923.html
Thanks,
Radhey
