linux-kernel - Re: [PATCH V3 1/2] bdisp: Fix a possible sleep-in-atomic bug in bdisp_hw

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Date:   Tue, 19 Dec 2017 16:18:30 +0000
From:   Fabien DESSENNE <fabien.dessenne@...com>
To:     Jia-Ju Bai <baijiaju1990@...il.com>,
        "mchehab@...nel.org" <mchehab@...nel.org>,
        Benjamin GAIGNARD <benjamin.gaignard@...com>,
        "hverkuil@...all.nl" <hverkuil@...all.nl>
CC:     "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V3 1/2] bdisp: Fix a possible sleep-in-atomic bug in
 bdisp_hw_reset

Hi,


It's almost good!

You have to fix these checkpatch Warning/Check:

WARNING: Block comments use a trailing */ on a separate line
#36: FILE: drivers/media/platform/sti/bdisp/bdisp-hw.c:383:
+     * needing any delays */

CHECK: Alignment should match open parenthesis
#38: FILE: drivers/media/platform/sti/bdisp/bdisp-hw.c:385:
+    if (readl_poll_timeout_atomic(bdisp->regs + BLT_STA1, tmp,
+        (tmp & BLT_STA1_IDLE), POLL_RST_DELAY_MS,


 From kernel documentation in the "Posting patches" chapter:

"You should always run patches through scripts/checkpatch.pl and address 
the complaints it comes up with."

And, please use the --strict option

Thanks for your understanding.

BR

Fabien

On 19/12/17 14:57, 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 |   23 ++++++++++++-----------
>   1 file changed, 12 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/media/platform/sti/bdisp/bdisp-hw.c b/drivers/media/platform/sti/bdisp/bdisp-hw.c
> index b7892f3..b63d9c9 100644
> --- a/drivers/media/platform/sti/bdisp/bdisp-hw.c
> +++ b/drivers/media/platform/sti/bdisp/bdisp-hw.c
> @@ -4,7 +4,7 @@
>    * License terms:  GNU General Public License (GPL), version 2
>    */
>   
> -#include <linux/delay.h>
> +#include <linux/iopoll.h>
>   
>   #include "bdisp.h"
>   #include "bdisp-filter.h"
> @@ -15,7 +15,7 @@
>   
>   /* Reset & boot poll config */
>   #define POLL_RST_MAX            50
> -#define POLL_RST_DELAY_MS       20
> +#define POLL_RST_DELAY_US       20000
>   
>   enum bdisp_target_plan {
>   	BDISP_RGB,
> @@ -366,7 +366,7 @@ struct bdisp_filter_addr {
>    */
>   int bdisp_hw_reset(struct bdisp_dev *bdisp)
>   {
> -	unsigned int i;
> +	u32 tmp;
>   
>   	dev_dbg(bdisp->dev, "%s\n", __func__);
>   
> @@ -378,16 +378,17 @@ int bdisp_hw_reset(struct bdisp_dev *bdisp)
>   	       bdisp->regs + BLT_CTL);
>   	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)
> +	/* Wait for reset done.
> +	 * Despite the large timeout, most of the time the reset happens without
> +	 * needing any delays */

shall be

+	 * needing any delays

+	 */

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

shall be:

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

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