linux-kernel - Re: [PATCH v2] media: sti: bdisp: fix a possible sleep-in-atomic-context bug in bdisp_device

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Date:   Thu, 19 Dec 2019 11:14:26 +0000
From:   Fabien DESSENNE <fabien.dessenne@...com>
To:     Jia-Ju Bai <baijiaju1990@...il.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] media: sti: bdisp: fix a possible
 sleep-in-atomic-context bug in bdisp_device_run()

Thank you!


On 19/12/2019 11:34 AM, Jia-Ju Bai wrote:
> The driver may sleep while holding a spinlock.
> The function call path (from bottom to top) in Linux 4.19 is:
>
> drivers/media/platform/sti/bdisp/bdisp-hw.c, 385:
>      msleep in bdisp_hw_reset
> drivers/media/platform/sti/bdisp/bdisp-v4l2.c, 341:
>      bdisp_hw_reset in bdisp_device_run
> drivers/media/platform/sti/bdisp/bdisp-v4l2.c, 317:
>      _raw_spin_lock_irqsave in bdisp_device_run
>
> To fix this bug, msleep() is replaced with udelay().
>
> This bug is found by a static analysis tool STCheck written by myself.
>
> Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>


Reviewed-by: Fabien Dessenne <fabien.dessenne@...com>


> ---
> v2:
> * Use udelay() instead of mdelay().
>    Thank Fabien for good advice.
>
> ---
>   drivers/media/platform/sti/bdisp/bdisp-hw.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/media/platform/sti/bdisp/bdisp-hw.c b/drivers/media/platform/sti/bdisp/bdisp-hw.c
> index 4372abbb5950..a74e9fd65238 100644
> --- a/drivers/media/platform/sti/bdisp/bdisp-hw.c
> +++ b/drivers/media/platform/sti/bdisp/bdisp-hw.c
> @@ -14,8 +14,8 @@
>   #define MAX_SRC_WIDTH           2048
>   
>   /* Reset & boot poll config */
> -#define POLL_RST_MAX            50
> -#define POLL_RST_DELAY_MS       20
> +#define POLL_RST_MAX            500
> +#define POLL_RST_DELAY_MS       2
>   
>   enum bdisp_target_plan {
>   	BDISP_RGB,
> @@ -382,7 +382,7 @@ int bdisp_hw_reset(struct bdisp_dev *bdisp)
>   	for (i = 0; i < POLL_RST_MAX; i++) {
>   		if (readl(bdisp->regs + BLT_STA1) & BLT_STA1_IDLE)
>   			break;
> -		msleep(POLL_RST_DELAY_MS);
> +		udelay(POLL_RST_DELAY_MS * 1000);
>   	}
>   	if (i == POLL_RST_MAX)
>   		dev_err(bdisp->dev, "Reset timeout\n");