From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bitan Biswas Subject: Re: [PATCH V4 6/6] i2c: tegra: remove BUG, BUG_ON Date: Tue, 11 Jun 2019 00:38:03 -0700 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"; format=flowed Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Dmitry Osipenko , 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 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 drivers/i2c/busses/i2c-tegra.c | 11 ++++++----- >>>> =C2=A0 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) >>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * prevent overwriting past the e= nd of buf >>>> =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_remaining= > 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=A0if (WARN_ON_ONCE(buf_remaining > 3)) >>> =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/i2c-= tegra.c#L520 >> >=20 > Ah yes, indeed! >=20 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-teg= ra.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-teg= ra.c#L515 I shall add the check for less than 3 in both RX and TX cases in a=20 separate patch in this series. >> >>> >>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 val =3D i2c_re= adl(i2c_dev, I2C_RX_FIFO); >>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 val =3D cpu_to= _le32(val); >>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 memcpy(buf, &v= al, buf_remaining); >>>> @@ -523,7 +522,6 @@ 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=C2=A0=C2=A0 rx_fifo_avail-= -; >>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } >>>> =C2=A0 -=C2=A0=C2=A0=C2=A0 BUG_ON(rx_fifo_avail > 0 && buf_remaining = > 0); >>> >>> Better not to ignore this as well: >>> >>> =C2=A0=C2=A0=C2=A0=C2=A0if (WARN_ON_ONCE(rx_fifo_avail > 0 && >>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0 buf_remaining > 0)) >>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 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: >=20 > [1] Okay, but it doesn't ensure about rx_fifo_avail. So it could be: >=20 > if (WARN_ON_ONCE(rx_fifo_avail)) > return -EINVAL; I shall add the WARN_ON_ONCE. >=20 >>>> -=C2=A0=C2=A0=C2=A0 BUG_ON(rx_fifo_avail > 0 && buf_remaining > 0); >> >>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 i2c_dev->msg_buf_remaining =3D buf_rem= aining; >>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 i2c_dev->msg_buf =3D buf; >>>> =C2=A0 @@ -581,7 +579,6 @@ static int tegra_i2c_fill_tx_fifo(struct >>>> tegra_i2c_dev *i2c_dev) >>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * boundary and fault. >>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 */ >>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (tx_fifo_avail > 0 && buf_remaining= > 0) { >>>> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 BUG_ON(buf_remaining > 3); >>> >>> And here, cause this will corrupt stack: >>> >>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (WARN_ON_ONCE(buf_remain= ing > 3)) >>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ret= urn -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. >=20 > Okay, agree here. >=20 >>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 memcpy(&val, b= uf, buf_remaining); >>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 val =3D le32_t= o_cpu(val); >>>> =C2=A0 @@ -850,7 +847,8 @@ static irqreturn_t tegra_i2c_isr(int irq, = void >>>> *dev_id) >>>> =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 (i2c_dev->msg_buf_remaining) >>>> =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=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=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0 else >>>> -=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 BUG(); >>>> +=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 tegra_i2c_mask_irq(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=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0 I2C_INT_RX_FIFO_DATA_REQ); >>> >>> Then here: >>> >>> =C2=A0=C2=A0=C2=A0=C2=A0if (WARN_ON_ONCE(!i2c_dev->msg_buf_remaining) = || >>> =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 i2c_dev->msg_err |=3D I2C_E= RR_UNKNOWN_INTERRUPT; >>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 goto err; >>> =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 if (WARN_ON_ONCE(!i2c_dev->msg_buf_remaining)= || >>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 tegra_i2c_empty_rx_fi= fo(i2c_dev)) { >=20 > 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. >=20 > 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: >=20 > if (tegra_i2c_empty_rx_fifo(i2c_dev)) { > i2c_dev->msg_err |=3D I2C_ERR_UNKNOWN_INTERRUPT; > goto err; > } >=20 In the case "if (status & I2C_INT_PACKET_XFER_COMPLETE) {" , we do not=20 have any tegra_i2c_empty_rx_fifo call today. In this current driver I do=20 not see any code that checks for the buffer space and prevents RX FIFO=20 from being drained. The transfer complete when seen must have already=20 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-teg= ra.c#L860 So we can put the "WARN_ON_ONCE(i2c_dev->msg_buf_remaining) with msg_err=20 assignment and goto err" to confirm if some corner case is not handled. Planning to share updated patch. -Thanks, Bitan