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SubjectRe: [PATCH V2 1/2] bdisp: Fix a possible sleep-in-atomic bug in bdisp_hw_reset
Date
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@gmail.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;
> }
>
> /**
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