Re: [PATCH 1/1] dma: actions: Fix lockdep splat for owl-dma

[Cristian Ciocaltea <cristian.ciocaltea@gmail.com>]

On Tue, Apr 28, 2020 at 10:19:21PM +0530, Manivannan Sadhasivam wrote:
> Hi,
> 
> On Tue, Apr 28, 2020 at 01:56:12PM +0300, Cristian Ciocaltea wrote:
> > When the kernel is build with lockdep support and the owl-dma driver is
> > used, the following message is shown:
> > 
> > [    2.496939] INFO: trying to register non-static key.
> > [    2.501889] the code is fine but needs lockdep annotation.
> > [    2.507357] turning off the locking correctness validator.
> > [    2.512834] CPU: 0 PID: 12 Comm: kworker/0:1 Not tainted 5.6.3+ #15
> > [    2.519084] Hardware name: Generic DT based system
> > [    2.523878] Workqueue: events_freezable mmc_rescan
> > [    2.528681] [<801127f0>] (unwind_backtrace) from [<8010da58>] (show_stack+0x10/0x14)
> > [    2.536420] [<8010da58>] (show_stack) from [<8080fbe8>] (dump_stack+0xb4/0xe0)
> > [    2.543645] [<8080fbe8>] (dump_stack) from [<8017efa4>] (register_lock_class+0x6f0/0x718)
> > [    2.551816] [<8017efa4>] (register_lock_class) from [<8017b7d0>] (__lock_acquire+0x78/0x25f0)
> > [    2.560330] [<8017b7d0>] (__lock_acquire) from [<8017e5e4>] (lock_acquire+0xd8/0x1f4)
> > [    2.568159] [<8017e5e4>] (lock_acquire) from [<80831fb0>] (_raw_spin_lock_irqsave+0x3c/0x50)
> > [    2.576589] [<80831fb0>] (_raw_spin_lock_irqsave) from [<8051b5fc>] (owl_dma_issue_pending+0xbc/0x120)
> > [    2.585884] [<8051b5fc>] (owl_dma_issue_pending) from [<80668cbc>] (owl_mmc_request+0x1b0/0x390)
> > [    2.594655] [<80668cbc>] (owl_mmc_request) from [<80650ce0>] (mmc_start_request+0x94/0xbc)
> > [    2.602906] [<80650ce0>] (mmc_start_request) from [<80650ec0>] (mmc_wait_for_req+0x64/0xd0)
> > [    2.611245] [<80650ec0>] (mmc_wait_for_req) from [<8065aa10>] (mmc_app_send_scr+0x10c/0x144)
> > [    2.619669] [<8065aa10>] (mmc_app_send_scr) from [<80659b3c>] (mmc_sd_setup_card+0x4c/0x318)
> > [    2.628092] [<80659b3c>] (mmc_sd_setup_card) from [<80659f0c>] (mmc_sd_init_card+0x104/0x430)
> > [    2.636601] [<80659f0c>] (mmc_sd_init_card) from [<8065a3e0>] (mmc_attach_sd+0xcc/0x16c)
> > [    2.644678] [<8065a3e0>] (mmc_attach_sd) from [<8065301c>] (mmc_rescan+0x3ac/0x40c)
> > [    2.652332] [<8065301c>] (mmc_rescan) from [<80143244>] (process_one_work+0x2d8/0x780)
> > [    2.660239] [<80143244>] (process_one_work) from [<80143730>] (worker_thread+0x44/0x598)
> > [    2.668323] [<80143730>] (worker_thread) from [<8014b5f8>] (kthread+0x148/0x150)
> > [    2.675708] [<8014b5f8>] (kthread) from [<801010b4>] (ret_from_fork+0x14/0x20)
> > [    2.682912] Exception stack(0xee8fdfb0 to 0xee8fdff8)
> > [    2.687954] dfa0:                                     00000000 00000000 00000000 00000000
> > [    2.696118] dfc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
> > [    2.704277] dfe0: 00000000 00000000 00000000 00000000 00000013 00000000
> > 
> > The required fix is to use spin_lock_init() on the pchan lock before
> > attempting to call any spin_lock_irqsave() in owl_dma_get_pchan().
> > 
> 
> Right, this is a bug. But while looking at the code now, I feel that we don't
> need 'pchan->lock'. The idea was to protect 'pchan->vchan', but I think
> 'od->lock' is the better candidate for that since it already protects it in
> 'owl_dma_terminate_pchan'.
> 
> So I'd be happy if you remove the lock from 'pchan' and just directly use the
> one in 'od'.
> 
> Out of curiosity, on which platform you're testing this?
> 
> Thanks,
> Mani
> 

Hi Mani,

Totally agree, I will send a new patch revision as soon as I do some
more testing.

I'm currently experimenting on an Actions S500 based board (Roseapple Pi)
trying to extend, if possible, the existing mainline support for those
SoCs. I don't have much progress so far, since I started quite recently
and I also lack experience in the kernel development area, but I do my
best to come back with more patches once I get a consistent functionality.

Thanks a lot for your support,
Cristi

> > Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@gmail.com>
> > ---
> >  drivers/dma/owl-dma.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/drivers/dma/owl-dma.c b/drivers/dma/owl-dma.c
> > index c683051257fd..d9d0f0488e70 100644
> > --- a/drivers/dma/owl-dma.c
> > +++ b/drivers/dma/owl-dma.c
> > @@ -1131,6 +1131,7 @@ static int owl_dma_probe(struct platform_device *pdev)
> >  
> >  		pchan->id = i;
> >  		pchan->base = od->base + OWL_DMA_CHAN_BASE(i);
> > +		spin_lock_init(&pchan->lock);
> >  	}
> >  
> >  	/* Init virtual channel */
> > -- 
> > 2.26.2
> >