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Subject: Re: [PATCH V4 6/6] i2c: tegra: remove BUG, BUG_ON
To:     Bitan Biswas <bbiswas@nvidia.com>,
        Laxman Dewangan <ldewangan@nvidia.com>,
        Thierry Reding <treding@nvidia.com>,
        Jonathan Hunter <jonathanh@nvidia.com>,
        linux-i2c@vger.kernel.org, linux-tegra@vger.kernel.org,
        linux-kernel@vger.kernel.org, Peter Rosin <peda@axentia.se>,
        Wolfram Sang <wsa@the-dreams.de>
Cc:     Shardar Mohammed <smohammed@nvidia.com>,
        Sowjanya Komatineni <skomatineni@nvidia.com>,
        Mantravadi Karthik <mkarthik@nvidia.com>
References: <1560186515-30797-1-git-send-email-bbiswas@nvidia.com>
 <1560186515-30797-6-git-send-email-bbiswas@nvidia.com>
From:   Dmitry Osipenko <digetx@gmail.com>
Message-ID: <06ab30b6-bf79-c628-0a04-d0307511a06f@gmail.com>
Date:   Mon, 10 Jun 2019 21:12:22 +0300
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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;
>