Re: [PATCH 1/3] dma: xilinx_dpdma: Fix locking

[Tomi Valkeinen]

On 08/03/2024 23:00, Sean Anderson wrote:
> There are several places where either chan->lock or chan->vchan.lock was
> not held. Add appropriate locking. This fixes lockdep warnings like

Reviewed-by: Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx>

 Tomi

> [   31.077578] ------------[ cut here ]------------
> [   31.077831] WARNING: CPU: 2 PID: 40 at drivers/dma/xilinx/xilinx_dpdma.c:834 xilinx_dpdma_chan_queue_transfer+0x274/0x5e0
> [   31.077953] Modules linked in:
> [   31.078019] CPU: 2 PID: 40 Comm: kworker/u12:1 Not tainted 6.6.20+ #98
> [   31.078102] Hardware name: xlnx,zynqmp (DT)
> [   31.078169] Workqueue: events_unbound deferred_probe_work_func
> [   31.078272] pstate: 600000c5 (nZCv daIF -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> [   31.078377] pc : xilinx_dpdma_chan_queue_transfer+0x274/0x5e0
> [   31.078473] lr : xilinx_dpdma_chan_queue_transfer+0x270/0x5e0
> [   31.078550] sp : ffffffc083bb2e10
> [   31.078590] x29: ffffffc083bb2e10 x28: 0000000000000000 x27: ffffff880165a168
> [   31.078754] x26: ffffff880164e920 x25: ffffff880164eab8 x24: ffffff880164d480
> [   31.078920] x23: ffffff880165a148 x22: ffffff880164e988 x21: 0000000000000000
> [   31.079132] x20: ffffffc082aa3000 x19: ffffff880164e880 x18: 0000000000000000
> [   31.079295] x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000
> [   31.079453] x14: 0000000000000000 x13: ffffff8802263dc0 x12: 0000000000000001
> [   31.079613] x11: 0001ffc083bb2e34 x10: 0001ff880164e98f x9 : 0001ffc082aa3def
> [   31.079824] x8 : 0001ffc082aa3dec x7 : 0000000000000000 x6 : 0000000000000516
> [   31.079982] x5 : ffffffc7f8d43000 x4 : ffffff88003c9c40 x3 : ffffffffffffffff
> [   31.080147] x2 : ffffffc7f8d43000 x1 : 00000000000000c0 x0 : 0000000000000000
> [   31.080307] Call trace:
> [   31.080340]  xilinx_dpdma_chan_queue_transfer+0x274/0x5e0
> [   31.080518]  xilinx_dpdma_issue_pending+0x11c/0x120
> [   31.080595]  zynqmp_disp_layer_update+0x180/0x3ac
> [   31.080712]  zynqmp_dpsub_plane_atomic_update+0x11c/0x21c
> [   31.080825]  drm_atomic_helper_commit_planes+0x20c/0x684
> [   31.080951]  drm_atomic_helper_commit_tail+0x5c/0xb0
> [   31.081139]  commit_tail+0x234/0x294
> [   31.081246]  drm_atomic_helper_commit+0x1f8/0x210
> [   31.081363]  drm_atomic_commit+0x100/0x140
> [   31.081477]  drm_client_modeset_commit_atomic+0x318/0x384
> [   31.081634]  drm_client_modeset_commit_locked+0x8c/0x24c
> [   31.081725]  drm_client_modeset_commit+0x34/0x5c
> [   31.081812]  __drm_fb_helper_restore_fbdev_mode_unlocked+0x104/0x168
> [   31.081899]  drm_fb_helper_set_par+0x50/0x70
> [   31.081971]  fbcon_init+0x538/0xc48
> [   31.082047]  visual_init+0x16c/0x23c
> [   31.082207]  do_bind_con_driver.isra.0+0x2d0/0x634
> [   31.082320]  do_take_over_console+0x24c/0x33c
> [   31.082429]  do_fbcon_takeover+0xbc/0x1b0
> [   31.082503]  fbcon_fb_registered+0x2d0/0x34c
> [   31.082663]  register_framebuffer+0x27c/0x38c
> [   31.082767]  __drm_fb_helper_initial_config_and_unlock+0x5c0/0x91c
> [   31.082939]  drm_fb_helper_initial_config+0x50/0x74
> [   31.083012]  drm_fbdev_dma_client_hotplug+0xb8/0x108
> [   31.083115]  drm_client_register+0xa0/0xf4
> [   31.083195]  drm_fbdev_dma_setup+0xb0/0x1cc
> [   31.083293]  zynqmp_dpsub_drm_init+0x45c/0x4e0
> [   31.083431]  zynqmp_dpsub_probe+0x444/0x5e0
> [   31.083616]  platform_probe+0x8c/0x13c
> [   31.083713]  really_probe+0x258/0x59c
> [   31.083793]  __driver_probe_device+0xc4/0x224
> [   31.083878]  driver_probe_device+0x70/0x1c0
> [   31.083961]  __device_attach_driver+0x108/0x1e0
> [   31.084052]  bus_for_each_drv+0x9c/0x100
> [   31.084125]  __device_attach+0x100/0x298
> [   31.084207]  device_initial_probe+0x14/0x20
> [   31.084292]  bus_probe_device+0xd8/0xdc
> [   31.084368]  deferred_probe_work_func+0x11c/0x180
> [   31.084451]  process_one_work+0x3ac/0x988
> [   31.084643]  worker_thread+0x398/0x694
> [   31.084752]  kthread+0x1bc/0x1c0
> [   31.084848]  ret_from_fork+0x10/0x20
> [   31.084932] irq event stamp: 64549
> [   31.084970] hardirqs last  enabled at (64548): [<ffffffc081adf35c>] _raw_spin_unlock_irqrestore+0x80/0x90
> [   31.085157] hardirqs last disabled at (64549): [<ffffffc081adf010>] _raw_spin_lock_irqsave+0xc0/0xdc
> [   31.085277] softirqs last  enabled at (64503): [<ffffffc08001071c>] __do_softirq+0x47c/0x500
> [   31.085390] softirqs last disabled at (64498): [<ffffffc080017134>] ____do_softirq+0x10/0x1c
> [   31.085501] ---[ end trace 0000000000000000 ]---
>
> Fixes: 7cbb0c63de3f ("dmaengine: xilinx: dpdma: Add the Xilinx DisplayPort DMA engine driver")
> Signed-off-by: Sean Anderson <sean.anderson@xxxxxxxxx>
> ---
>
>   drivers/dma/xilinx/xilinx_dpdma.c | 13 ++++++++++---
>   1 file changed, 10 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/dma/xilinx/xilinx_dpdma.c b/drivers/dma/xilinx/xilinx_dpdma.c
> index b82815e64d24..eb0637d90342 100644
> --- a/drivers/dma/xilinx/xilinx_dpdma.c
> +++ b/drivers/dma/xilinx/xilinx_dpdma.c
> @@ -214,7 +214,8 @@ struct xilinx_dpdma_tx_desc {
>    * @running: true if the channel is running
>    * @first_frame: flag for the first frame of stream
>    * @video_group: flag if multi-channel operation is needed for video channels
> - * @lock: lock to access struct xilinx_dpdma_chan
> + * @lock: lock to access struct xilinx_dpdma_chan. Must be taken before
> + *        @vchan.lock, if both are to be held.
>    * @desc_pool: descriptor allocation pool
>    * @err_task: error IRQ bottom half handler
>    * @desc: References to descriptors being processed
> @@ -1097,12 +1098,14 @@ static void xilinx_dpdma_chan_vsync_irq(struct  xilinx_dpdma_chan *chan)
>   	 * Complete the active descriptor, if any, promote the pending
>   	 * descriptor to active, and queue the next transfer, if any.
>   	 */
> +	spin_lock(&chan->vchan.lock);
>   	if (chan->desc.active)
>   		vchan_cookie_complete(&chan->desc.active->vdesc);
>   	chan->desc.active = pending;
>   	chan->desc.pending = NULL;
>   
>   	xilinx_dpdma_chan_queue_transfer(chan);
> +	spin_unlock(&chan->vchan.lock);
>   
>   out:
>   	spin_unlock_irqrestore(&chan->lock, flags);
> @@ -1264,10 +1267,12 @@ static void xilinx_dpdma_issue_pending(struct dma_chan *dchan)
>   	struct xilinx_dpdma_chan *chan = to_xilinx_chan(dchan);
>   	unsigned long flags;
>   
> -	spin_lock_irqsave(&chan->vchan.lock, flags);
> +	spin_lock_irqsave(&chan->lock, flags);
> +	spin_lock(&chan->vchan.lock);
>   	if (vchan_issue_pending(&chan->vchan))
>   		xilinx_dpdma_chan_queue_transfer(chan);
> -	spin_unlock_irqrestore(&chan->vchan.lock, flags);
> +	spin_unlock(&chan->vchan.lock);
> +	spin_unlock_irqrestore(&chan->lock, flags);
>   }
>   
>   static int xilinx_dpdma_config(struct dma_chan *dchan,
> @@ -1495,7 +1500,9 @@ static void xilinx_dpdma_chan_err_task(struct tasklet_struct *t)
>   		    XILINX_DPDMA_EINTR_CHAN_ERR_MASK << chan->id);
>   
>   	spin_lock_irqsave(&chan->lock, flags);
> +	spin_lock(&chan->vchan.lock);
>   	xilinx_dpdma_chan_queue_transfer(chan);
> +	spin_unlock(&chan->vchan.lock);
>   	spin_unlock_irqrestore(&chan->lock, flags);
>   }
>