Re: [PATCH V4 6/6] i2c: tegra: remove BUG, BUG_ON

Dmitry Osipenko
2019-06-10T18:12:28Z

10.06.2019 20:08, Bitan Biswas пишет:
> Remove redundant BUG_ON calls or replace with WARN_ON_ONCE
> as needed. Remove BUG() and make Rx and Tx case handling
> similar.
>
> Signed-off-by: Bitan Biswas <bbiswas@nvidia.com>
> ---
> drivers/i2c/busses/i2c-tegra.c | 11 ++++++-----
> 1 file changed, 6 insertions(+), 5 deletions(-)

Looks that this is still not correct. What if it transfer-complete flag
is set and buffer is full on RX? In this case the transfer will succeed
while it was a failure.

> diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
> index 4dfb4c1..30619d6 100644
> --- a/drivers/i2c/busses/i2c-tegra.c
> +++ b/drivers/i2c/busses/i2c-tegra.c
> @@ -515,7 +515,6 @@ static int tegra_i2c_empty_rx_fifo(struct tegra_i2c_dev *i2c_dev)
> * prevent overwriting past the end of buf
> */
> if (rx_fifo_avail > 0 && buf_remaining > 0) {
> - BUG_ON(buf_remaining > 3);

Actually error should be returned here since out-of-bounds memory
accesses must be avoided, hence:

if (WARN_ON_ONCE(buf_remaining > 3))
return -EINVAL;

> val = i2c_readl(i2c_dev, I2C_RX_FIFO);
> val = cpu_to_le32(val);
> memcpy(buf, &val, buf_remaining);
> @@ -523,7 +522,6 @@ static int tegra_i2c_empty_rx_fifo(struct tegra_i2c_dev *i2c_dev)
> rx_fifo_avail--;
> }
>
> - BUG_ON(rx_fifo_avail > 0 && buf_remaining > 0);

Better not to ignore this as well:

if (WARN_ON_ONCE(rx_fifo_avail > 0 &&
buf_remaining > 0))
return -EINVAL;

> i2c_dev->msg_buf_remaining = buf_remaining;
> i2c_dev->msg_buf = buf;
>
> @@ -581,7 +579,6 @@ static int tegra_i2c_fill_tx_fifo(struct tegra_i2c_dev *i2c_dev)
> * boundary and fault.
> */
> if (tx_fifo_avail > 0 && buf_remaining > 0) {
> - BUG_ON(buf_remaining > 3);

And here, cause this will corrupt stack:

if (WARN_ON_ONCE(buf_remaining > 3))
return -EINVAL;

> memcpy(&val, buf, buf_remaining);
> val = le32_to_cpu(val);
>
> @@ -850,7 +847,8 @@ static irqreturn_t tegra_i2c_isr(int irq, void *dev_id)
> if (i2c_dev->msg_buf_remaining)
> tegra_i2c_empty_rx_fifo(i2c_dev);
> else
> - BUG();
> + tegra_i2c_mask_irq(i2c_dev,
> + I2C_INT_RX_FIFO_DATA_REQ);

Then here:

if (WARN_ON_ONCE(!i2c_dev->msg_buf_remaining) ||
tegra_i2c_empty_rx_fifo(i2c_dev)) {
i2c_dev->msg_err |= I2C_ERR_UNKNOWN_INTERRUPT;
goto err;
}

> }
>
> if (!i2c_dev->msg_read && (status & I2C_INT_TX_FIFO_DATA_REQ)) {
> @@ -876,7 +874,10 @@ static irqreturn_t tegra_i2c_isr(int irq, void *dev_id)
> if (status & I2C_INT_PACKET_XFER_COMPLETE) {
> if (i2c_dev->is_curr_dma_xfer)
> i2c_dev->msg_buf_remaining = 0;
> - BUG_ON(i2c_dev->msg_buf_remaining);
> + if (WARN_ON_ONCE(i2c_dev->msg_buf_remaining)) {
> + i2c_dev->msg_err |= I2C_ERR_UNKNOWN_INTERRUPT;
> + goto err;
> + }
> complete(&i2c_dev->msg_complete);
> }
> goto done;
>