linux-kernel - Re: [PATCH V2 1/2] bdisp: Fix a possible sleep-in-atomic bug in bdisp_hw

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Date:   Tue, 19 Dec 2017 10:43:22 +0000
From:   Fabien DESSENNE <fabien.dessenne@...com>
To:     Jia-Ju Bai <baijiaju1990@...il.com>,
        "hverkuil@...all.nl" <hverkuil@...all.nl>,
        Benjamin GAIGNARD <benjamin.gaignard@...com>,
        "mchehab@...nel.org" <mchehab@...nel.org>
CC:     "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 1/2] bdisp: Fix a possible sleep-in-atomic bug in
 bdisp_hw_reset

Hi,


On 16/12/17 12:54, Jia-Ju Bai wrote:
> The driver may sleep under a spinlock.
> The function call path is:
> bdisp_device_run (acquire the spinlock)
>    bdisp_hw_reset
>      msleep --> may sleep
>
> To fix it, readl_poll_timeout_atomic is used to replace msleep.
>
> This bug is found by my static analysis tool(DSAC) and
> checked by my code review.
>
> Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
> ---
>   drivers/media/platform/sti/bdisp/bdisp-hw.c |   16 ++++++++--------
>   1 file changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/media/platform/sti/bdisp/bdisp-hw.c b/drivers/media/platform/sti/bdisp/bdisp-hw.c
> index b7892f3..e94a371 100644
> --- a/drivers/media/platform/sti/bdisp/bdisp-hw.c
> +++ b/drivers/media/platform/sti/bdisp/bdisp-hw.c
> @@ -5,6 +5,7 @@
>    */
>   
>   #include <linux/delay.h>

This delay.h include is no more needed, remove it.

> +#include <linux/iopoll.h>
>   
>   #include "bdisp.h"
>   #include "bdisp-filter.h"
> @@ -366,7 +367,7 @@ struct bdisp_filter_addr {
>    */
>   int bdisp_hw_reset(struct bdisp_dev *bdisp)
>   {
> -	unsigned int i;
> +	u32 tmp;
>   
>   	dev_dbg(bdisp->dev, "%s\n", __func__);
>   
> @@ -379,15 +380,14 @@ int bdisp_hw_reset(struct bdisp_dev *bdisp)
>   	writel(0, bdisp->regs + BLT_CTL);
>   
>   	/* Wait for reset done */
> -	for (i = 0; i < POLL_RST_MAX; i++) {
> -		if (readl(bdisp->regs + BLT_STA1) & BLT_STA1_IDLE)
> -			break;
> -		msleep(POLL_RST_DELAY_MS);
> -	}
> -	if (i == POLL_RST_MAX)

As recommended by Mauro, please add this comment:
Despite the large timeout, most of the time the reset happens without 
needing any delays

> +	if (readl_poll_timeout_atomic(bdisp->regs + BLT_STA1, tmp,
> +		(tmp & BLT_STA1_IDLE), POLL_RST_DELAY_MS,
> +			POLL_RST_DELAY_MS * POLL_RST_MAX)) {

read_poll_timeout expects US timings, not MS.

>   		dev_err(bdisp->dev, "Reset timeout\n");
> +		return -EAGAIN;
> +	}
>   
> -	return (i == POLL_RST_MAX) ? -EAGAIN : 0;
> +	return 0;
>   }
>   
>   /**