Re: [PATCH] mtd: spi-nor: Reschedule in spi_nor_wait_till_ready()

[Bart Van Assche <bvanassche@acm.org>]

On 11/6/26 1:04 PM, Bart Van Assche wrote:
> In spi_nor_wait_till_ready_with_timeout(), cond_resched() is only
> called after spi_nor_ready() returns 0. If the flash is already ready on
> the first status check, the function returns before reaching
> cond_resched(). This happens e.g. under QEMU, where SPI NOR page
> programs and sector erases complete synchronously during the MMIO write,
> combined with a controller driver that polls without sleeping.
> Consequently, multi-sector erases in spi_nor_erase() and multi-page
> writes in spi_nor_write() may iterate over thousands of sectors or pages
> without ever yielding the CPU on kernels built without
> CONFIG_PREEMPTION, e.g. ARM32 kernels with CONFIG_PREEMPT_VOLUNTARY=y.
> This triggers soft lockup and RCU stall reports.
> 
> Move cond_resched() to the start of the polling loop such that every
> call reschedules if needed, even if the flash is ready on the first
> check. Doing this in the shared wait helper instead of in the
> spi_nor_erase() and spi_nor_write() loops covers all callers that wait
> for a program or erase operation to complete.
> 
> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
> ---
>   drivers/mtd/spi-nor/core.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
> index 90524c58602e..3e3b727d262e 100644
> --- a/drivers/mtd/spi-nor/core.c
> +++ b/drivers/mtd/spi-nor/core.c
> @@ -653,6 +653,8 @@ static int spi_nor_wait_till_ready_with_timeout(struct spi_nor *nor,
>   	deadline = jiffies + timeout_jiffies;
>   
>   	while (!timeout) {
> +		cond_resched();
> +
>   		if (time_after_eq(jiffies, deadline))
>   			timeout = 1;
>   
> @@ -661,8 +663,6 @@ static int spi_nor_wait_till_ready_with_timeout(struct spi_nor *nor,
>   			return ret;
>   		if (ret)
>   			return 0;
> -
> -		cond_resched();
>   	}
>   
>   	dev_dbg(nor->dev, "flash operation timed out\n");

(+Brian)

The following probably should be added to the above patch:

Fixes: a95ce92e4b28 ("mtd: spi-nor: improve wait-till-ready timeout loop").

Bart.