From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dmitry Osipenko Subject: Re: [PATCH V4 6/6] i2c: tegra: remove BUG, BUG_ON Date: Tue, 11 Jun 2019 00:00:24 +0300 Message-ID: References: <1560186515-30797-1-git-send-email-bbiswas@nvidia.com> <1560186515-30797-6-git-send-email-bbiswas@nvidia.com> <06ab30b6-bf79-c628-0a04-d0307511a06f@gmail.com> <851d7837-5b98-228e-d8c9-3c41be1fb2e0@nvidia.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <851d7837-5b98-228e-d8c9-3c41be1fb2e0@nvidia.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Bitan Biswas , Laxman Dewangan , Thierry Reding , Jonathan Hunter , linux-i2c@vger.kernel.org, linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org, Peter Rosin , Wolfram Sang Cc: Shardar Mohammed , Sowjanya Komatineni , Mantravadi Karthik List-Id: linux-tegra@vger.kernel.org 10.06.2019 22:41, Bitan Biswas пишет: > > > On 6/10/19 11:12 AM, Dmitry Osipenko wrote: >> 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 >>> --- >>>   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; > buf_remaining will be less than equal to 3 because of the expression > earlier > https://elixir.bootlin.com/linux/v5.2-rc4/source/drivers/i2c/busses/i2c-tegra.c#L520 > Ah yes, indeed! > >> >>>           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; >> > Please check below line. > https://elixir.bootlin.com/linux/v5.2-rc4/source/drivers/i2c/busses/i2c-tegra.c#L532 > > > It ensures that buf_remaining will be 0 and we never hit the BUG_ON as > follows: [1] Okay, but it doesn't ensure about rx_fifo_avail. So it could be: if (WARN_ON_ONCE(rx_fifo_avail)) return -EINVAL; >>> -    BUG_ON(rx_fifo_avail > 0 && buf_remaining > 0); > >>>       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; >> > Please check the line > https://elixir.bootlin.com/linux/v5.2-rc4/source/drivers/i2c/busses/i2c-tegra.c#L576 > > > It ensures buf_remaining will be less or equal to 3. Okay, agree here. >>>           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; >>     } >> > Can you please elaborate why the condition needs to be as follows > instead of " if (WARN_ON_ONCE(i2c_dev->msg_buf_remaining)) " ? > >>     if (WARN_ON_ONCE(!i2c_dev->msg_buf_remaining) || >>         tegra_i2c_empty_rx_fifo(i2c_dev)) { Because this is a "receive" transfer and hence it is a error condition if the data-message was already fully received and then there is another request from hardware to receive more data. So "!i2c_dev->msg_buf_remaining" is the error condition here because there is no more space in the buffer. Looking at this again, seems checking for "if (WARN_ON_ONCE(rx_fifo_avail))" in the above hunk [1] will be already enough since a not fully drained RX FIFO means that there is no enough space in the buffer. Then it could be: if (tegra_i2c_empty_rx_fifo(i2c_dev)) { i2c_dev->msg_err |= I2C_ERR_UNKNOWN_INTERRUPT; goto err; }