Re: [PATCH v2 1/1] dma: actions: Fix lockdep splat for owl-dma

[Manivannan Sadhasivam]

On Wed, Apr 29, 2020 at 02:01:54PM +0300, Cristian Ciocaltea wrote:
> When the kernel is built 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 obvious fix would be to use 'spin_lock_init()' on 'pchan->lock'
> before attempting to call 'spin_lock_irqsave()' in 'owl_dma_get_pchan()'.
> 
> However, according to Manivannan Sadhasivam, 'pchan->lock' was supposed
> to only protect 'pchan->vchan' while 'od->lock' does a similar job in
> 'owl_dma_terminate_pchan'.
> 
> Therefore, this patch will simply substitute 'pchan->lock' with 'od->lock'
> and removes the 'lock' attribute in 'owl_dma_pchan' struct.
> 
> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@xxxxxxxxx>

Just one minor thing below, other than that,

Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx>

Thanks for doing this!

> ---
> Changes in v2:
> * Improve the fix as suggested by Manivannan Sadhasivam: substitute 
>   'pchan->lock' with 'od->lock' and get rid of the 'lock' attribute in
>   'owl_dma_pchan' struct
> * Update the commit message to reflect the changes
> 
>  drivers/dma/owl-dma.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/dma/owl-dma.c b/drivers/dma/owl-dma.c
> index c683051257fd..5b1c715a56c8 100644
> --- a/drivers/dma/owl-dma.c
> +++ b/drivers/dma/owl-dma.c
> @@ -181,7 +181,6 @@ struct owl_dma_pchan {
>  	u32			id;
>  	void __iomem		*base;
>  	struct owl_dma_vchan	*vchan;
> -	spinlock_t		lock;

You should also remove the kerneldoc comment for this lock.

Regards,
Mani

>  };
>  
>  /**
> @@ -437,14 +436,14 @@ static struct owl_dma_pchan *owl_dma_get_pchan(struct owl_dma *od,
>  	for (i = 0; i < od->nr_pchans; i++) {
>  		pchan = &od->pchans[i];
>  
> -		spin_lock_irqsave(&pchan->lock, flags);
> +		spin_lock_irqsave(&od->lock, flags);
>  		if (!pchan->vchan) {
>  			pchan->vchan = vchan;
> -			spin_unlock_irqrestore(&pchan->lock, flags);
> +			spin_unlock_irqrestore(&od->lock, flags);
>  			break;
>  		}
>  
> -		spin_unlock_irqrestore(&pchan->lock, flags);
> +		spin_unlock_irqrestore(&od->lock, flags);
>  	}
>  
>  	return pchan;
> -- 
> 2.26.2
>