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Date:   Sat, 2 May 2020 20:35:00 +0300
From:   Cristian Ciocaltea <cristian.ciocaltea@...il.com>
To:     Vinod Koul <vkoul@...nel.org>
Cc:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Andreas Färber <afaerber@...e.de>,
        Dan Williams <dan.j.williams@...el.com>,
        dmaengine@...r.kernel.org, linux-actions@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/1] dma: actions: Fix lockdep splat for owl-dma

On Sat, May 02, 2020 at 05:53:33PM +0530, Vinod Koul wrote:
> 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.
>

Hi Vinod,

Thank you for reviewing and sorry for the mistakes! I'll be more careful
next time with all those details.

I've submitted the updated patch: [PATCH v4 1/1] dmaengine: owl: Use
correct lock in owl_dma_get_pchan()

Kind regards,
Cristi

> > 
> > [    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@...il.com>
> > Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> > ---
> > 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

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