Messages in this thread Patch in this message | | | Subject | Re: [PATCH V4 6/6] i2c: tegra: remove BUG, BUG_ON | From | Bitan Biswas <> | Date | Tue, 11 Jun 2019 00:38:03 -0700 |
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On 6/10/19 2:00 PM, Dmitry Osipenko wrote: > 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 <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; >> 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! > I see that I am wrong and buf_remaining > 3 needs to be prevented at
https://elixir.bootlin.com/linux/v5.2-rc4/source/drivers/i2c/busses/i2c-tegra.c#L528
because of word_to_transfer is limited to rx_fifo_avail:
https://elixir.bootlin.com/linux/v5.2-rc4/source/drivers/i2c/busses/i2c-tegra.c#L515
I shall add the check for less than 3 in both RX and TX cases in a separate patch in this series.
>> >>> >>>> 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; I shall add the WARN_ON_ONCE.
> >>>> - 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; > } > In the case "if (status & I2C_INT_PACKET_XFER_COMPLETE) {" , we do not have any tegra_i2c_empty_rx_fifo call today. In this current driver I do not see any code that checks for the buffer space and prevents RX FIFO from being drained. The transfer complete when seen must have already consumed all bytes of msg_buf_remaining in the call at the line
https://elixir.bootlin.com/linux/v5.2-rc4/source/drivers/i2c/busses/i2c-tegra.c#L860
So we can put the "WARN_ON_ONCE(i2c_dev->msg_buf_remaining) with msg_err assignment and goto err" to confirm if some corner case is not handled.
Planning to share updated patch.
-Thanks, Bitan
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