Re: [PATCH v3 1/1] dma: actions: Fix lockdep splat for owl-dma

[Vinod Koul]

Hi Cristian,

On 29-04-20, 18:28, Cristian Ciocaltea wrote:
> When the kernel is built with lockdep support and the owl-dma driver is
> used, the following message is shown:

First the patch title needs upate, we describe the patch in the title
and not the cause. So use correct lock, or use od lock might be better
titles, pls revise.

Second, the susbsystem is named dmaengine:... not dma:.. You can always
check that by using git log on the respective file

Pls do add fixes and further acks received on next iteration.

> 
> [    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>
> Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx>
> ---
> Changes in v3:
> * Get rid of the kerneldoc comment for the removed struct attribute
> * Add the Reviewed-by tag in the commit message
> 
> 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 | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/dma/owl-dma.c b/drivers/dma/owl-dma.c
> index c683051257fd..66ef70b00ec0 100644
> --- a/drivers/dma/owl-dma.c
> +++ b/drivers/dma/owl-dma.c
> @@ -175,13 +175,11 @@ struct owl_dma_txd {
>   * @id: physical index to this channel
>   * @base: virtual memory base for the dma channel
>   * @vchan: the virtual channel currently being served by this physical channel
> - * @lock: a lock to use when altering an instance of this struct
>   */
>  struct owl_dma_pchan {
>  	u32			id;
>  	void __iomem		*base;
>  	struct owl_dma_vchan	*vchan;
> -	spinlock_t		lock;
>  };
>  
>  /**
> @@ -437,14 +435,14 @@ 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

-- 
~Vinod