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From: Bitan Biswas Message-ID: Date: Tue, 11 Jun 2019 11:22:49 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: X-Originating-IP: [10.124.1.5] X-ClientProxiedBy: HQMAIL101.nvidia.com (172.20.187.10) To HQMAIL107.nvidia.com (172.20.187.13) Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: quoted-printable DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1560277377; bh=Siey2IXCghQc1b+HjTOt8qDeeFID6nmkd3olmUxb5OY=; h=X-PGP-Universal:Subject:To:CC:References:From:Message-ID:Date: User-Agent:MIME-Version:In-Reply-To:X-Originating-IP: X-ClientProxiedBy:Content-Type:Content-Language: Content-Transfer-Encoding; b=CFAPmI/LgnAHMDhGQvW+GWcfzeKIqHr0L1N4KWE3LW3eDvTvuPSsYe/P3n6Ab6Bi6 HP7+K+pq7ve+uhbweTMadJIobofaeVy7C0qhihGdqfNWF5Uo+9vn/hCMKyf7UibQHp ryJo7D8GqWOUuYKoJGYyeQfGGErtWgtIiY41Q6/jEp9bjCWR0wvU47BHkxpVIZIU3n FN5e/xEeBY7sFM9JQPXABUbCv46fcHbPb+LokUQ1SAau0yMyhJMkCgypkg3ykHpN+7 CTfBK3A6DucXwvU8N2ByYGBfW1N+TI3jhFg48fn+gRZi9FBA81U8ZyaFAP/LbgcEMh DDRbDHtVpyraA== Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/11/19 4:34 AM, Dmitry Osipenko wrote: > 11.06.2019 10:38, Bitan Biswas =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >> >> >> On 6/10/19 2:00 PM, Dmitry Osipenko wrote: >>> 10.06.2019 22:41, Bitan Biswas =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >>>> >>>> >>>> On 6/10/19 11:12 AM, Dmitry Osipenko wrote: >>>>> 10.06.2019 20:08, Bitan Biswas =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >>>>>> 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 >>>>>> --- >>>>>> =C2=A0=C2=A0 drivers/i2c/busses/i2c-tegra.c | 11 ++++++----- >>>>>> =C2=A0=C2=A0 1 file changed, 6 insertions(+), 5 deletions(-) >>>>> >>>>> Looks that this is still not correct. What if it transfer-complete fl= ag >>>>> is set and buffer is full on RX? In this case the transfer will succe= ed >>>>> 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) >>>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * prevent overwriting pa= st the end of buf >>>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 */ >>>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (rx_fifo_avail > 0 && buf_r= emaining > 0) { >>>>>> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 BUG_ON(buf_remaining > 3= ); >>>>> >>>>> Actually error should be returned here since out-of-bounds memory >>>>> accesses must be avoided, hence: >>>>> >>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0if (WARN_ON_ONCE(buf_remaining > 3)) >>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 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/i2= c-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. >=20 > When word_to_transfer is more than rx_fifo_avail, then the rx_fifo_avail > becomes zero and hence the nibbles won't be copied. Please take a closer > look, the current code is correct, but the buf_remaining > 3 is unneeded > because it can't ever happen. >=20 > The code is structured the way that it's difficult to follow, apparently > the person who added the BUG_ON check in the first place couldn't follow > it either. Maybe it's worth to invest some more effort into refactoring > at least that part of the code. At minimum a clarifying comments would > be helpful. >=20 I shall try to add some comments near the BUG_ON check. > [snip] >=20 >>>>> Then here: >>>>> >>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0if (WARN_ON_ONCE(!i2c_dev->msg_buf_rem= aining) || >>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 tegra_i2c_empty_rx_= fifo(i2c_dev)) { >>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 i2c_dev->msg_err |= =3D I2C_ERR_UNKNOWN_INTERRUPT; >>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 goto err; >>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0} >>>>> >>>> Can you please elaborate why the condition needs to be as follows >>>> instead of " if (WARN_ON_ONCE(i2c_dev->msg_buf_remaining)) " ? >>>> >>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (WARN_ON_ONCE(!i2c_dev->msg_buf_re= maining) || >>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 tegra_i2c_emp= ty_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 anothe= r >>> 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: >>> >>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (tegra_i2c_empty_r= x_fifo(i2c_dev)) { >>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0 i2c_dev->msg_err |=3D I2C_ERR_UNKNOWN_INTERRUPT= ; >>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0 goto err; >>> =C2=A0=C2=A0=C2=A0=C2=A0} >>> >> 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. >=20 > There are two possible error conditions: >=20 > 1) Underflow: the XFER_COMPLETE happens before message is fully sent. >=20 > 2) Overflow: message is fully sent, but there is no XFER_COMPLETE and > then hardware asks to transfer more. >=20 > We are addressing the second case here, while you seems are confusing it > with the first case. >=20 Is the Overflow case pointed above corresponding to when=20 msg_buf_remaining is zero? If no, what indicates that message is fully=20 sent? I see that if msg_buf_remaining is already zero, the call=20 tegra_i2c_empty_rx_fifo will not do any copy of the bytes from FIFO to buf. One more point that is not clear to me is are the above suggestions you=20 made is corresponding to replacing below line in linux-next ? https://elixir.bootlin.com/linux/v5.2-rc4/source/drivers/i2c/busses/i2c-teg= ra.c#L888 Can you please also review the newly added patch "V5 6/7 "that was newly=20 posted? I think it is needed. -regards, Bitan