linux-kernel - Re: [PATCH] mmc: dw_mmc: Don't enable interrupts until we're ready

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Date:	Thu, 04 Sep 2014 14:21:53 +0900
From:	Jaehoon Chung <jh80.chung@...sung.com>
To:	Doug Anderson <dianders@...omium.org>,
	Seungwon Jeon <tgih.jun@...sung.com>,
	Jaehoon Chung <jh80.chung@...sung.com>,
	Ulf Hansson <ulf.hansson@...aro.org>
Cc:	Addy Ke <addy.ke@...k-chips.com>, linux-kernel@...r.kernel.org,
	linux-mmc@...r.kernel.org, chris@...ntf.net,
	Sonny Rao <sonnyrao@...omium.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] mmc: dw_mmc: Don't enable interrupts until we're ready

Hi Doug

On 09/03/2014 08:37 AM, Doug Anderson wrote:
> On dw_mmc there's a small race if you happen to get a card detect
> interrupt at just the wrong time during probe.  You may have enabled
> the interrupt but host->slot[0] may be NULL.
> 
> Fix the race by enabling interrupts all the way at the end of the
> probe.  We can also use free_irq() instead of dw_mmc specific masking
> to mask the IRQ at removal time.  Note that since we're now managing
> freeing of the irq ourselves, there's no need to use devm.
> 
> FYI, the crash would look like:
>   dwmmc_rockchip ff0c0000.dwmmc: DW MMC controller at irq 64, 32 bit host data width, 256 deep fifo
>   Unable to handle kernel NULL pointer dereference at virtual address 00000000
>   pgd = c0004000
>   [00000000] *pgd=00000000
>   ...
>   ...
>   [<c0499380>] (dw_mci_work_routine_card) from [<c0134b94>] (process_one_work+0x260/0x3c4)
>   [<c0134b94>] (process_one_work) from [<c0135b10>] (worker_thread+0x240/0x3a8)
>   [<c0135b10>] (worker_thread) from [<c013b64c>] (kthread+0x100/0x118)
>   [<c013b64c>] (kthread) from [<c0106418>] (ret_from_fork+0x14/0x20)
> 
> Signed-off-by: Doug Anderson <dianders@...omium.org>
> ---
> FYI: making dw_mmc into a module and trying module removal was not
> tested.  I'd appreciate any testing that folks can do there.  This
> code should be the equivalent and makes the error case of probe match
> the removal case more closely now.
> 
>  drivers/mmc/host/dw_mmc.c | 17 +++++++++++------
>  1 file changed, 11 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
> index 7f227e9..540ba3c 100644
> --- a/drivers/mmc/host/dw_mmc.c
> +++ b/drivers/mmc/host/dw_mmc.c
> @@ -2577,10 +2577,6 @@ int dw_mci_probe(struct dw_mci *host)
>  		goto err_dmaunmap;
>  	}
>  	INIT_WORK(&host->card_work, dw_mci_work_routine_card);
> -	ret = devm_request_irq(host->dev, host->irq, dw_mci_interrupt,
> -			       host->irq_flags, "dw-mci", host);
> -	if (ret)
> -		goto err_workqueue;
>  
>  	if (host->pdata->num_slots)
>  		host->num_slots = host->pdata->num_slots;
> @@ -2619,11 +2615,21 @@ int dw_mci_probe(struct dw_mci *host)
>  		goto err_workqueue;
>  	}
>  
> +	ret = request_irq(host->irq, dw_mci_interrupt, host->irq_flags,
> +			  "dw-mci", host);
> +	if (ret)
> +		goto err_initted;

I didn't test and consider race condition yet.
But if located "request_irq" at here, we can be confused something,
since there is "dev_info(host->dev, "%d slots initialized\n", init_slots)" message at above.

I think you can relocate this.

Best Regards,
Jaehoon Chung

> +
>  	if (host->quirks & DW_MCI_QUIRK_IDMAC_DTO)
>  		dev_info(host->dev, "Internal DMAC interrupt fix enabled.\n");
>  
>  	return 0;
>  
> +err_initted:
> +	for (i = 0; i < host->num_slots; i++)
> +		if (host->slot[i])
> +			dw_mci_cleanup_slot(host->slot[i], i);
> +
>  err_workqueue:
>  	destroy_workqueue(host->card_workqueue);
>  
> @@ -2649,8 +2655,7 @@ void dw_mci_remove(struct dw_mci *host)
>  {
>  	int i;
>  
> -	mci_writel(host, RINTSTS, 0xFFFFFFFF);
> -	mci_writel(host, INTMASK, 0); /* disable all mmc interrupt first */
> +	free_irq(host->irq, host);
>  
>  	for (i = 0; i < host->num_slots; i++) {
>  		dev_dbg(host->dev, "remove slot %d\n", i);
> 

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