[PATCH] MAX1111: Fix race condition causing NULL pointer exception

[linux@arm.linux.org.uk (Russell King - ARM Linux)]

On Wed, May 18, 2011 at 05:18:38PM +0200, Pavel Herrmann wrote:
> spi_sync call uses its spi_message parameter to keep completion information,
> having this structure static is not thread-safe, potentially causing one
> thread having pointers to memory on or above other threads stack. use
> per-call spi_message on stack to fix this

I assume this has not been tested with DMA debugging enabled.

The DMA API does not like mapping memory from the stack, which is what
you're potentially doing with this:

> +	uint8_t rx_buf[2] = {0, 0};
> +	uint8_t tx_buf = (channel << MAX1111_CTRL_SEL_SH) |
> +			MAX1111_CTRL_PD0 | MAX1111_CTRL_PD1 |
> +			MAX1111_CTRL_SGL | MAX1111_CTRL_UNI |
> +			MAX1111_CTRL_STR;
> +
> +	spi_message_init(&m);
> +	memset(t, 0, sizeof(t));
> +
> +	t[0].tx_buf = &tx_buf;
> +	t[0].len = 1;
> +	spi_message_add_tail(&t[0], &m);
> +
> +	t[1].rx_buf = rx_buf;
> +	t[1].len = 2;
> +	spi_message_add_tail(&t[1], &m);