[PATCHv2 1/2] mmc: block: Remove error check of hw_reset on reset

[PATCHv2 1/2] mmc: block: Remove error check of hw_reset on reset

[Christian Löhle]

Before switching back to the right partition in mmc_blk_reset
there used to be a check if hw_reset was even supported.
This return value was removed, so there is no reason to check.

Fixes: fefdd3c91e0a ("mmc: core: Drop superfluous validations in mmc_hw|sw_reset()")
Cc: stable@vger.kernel.org

Signed-off-by: Christian Loehle <cloehle@hyperstone.com>
---
-v2: Do not attempt to switch partitions if reset failed

 drivers/mmc/core/block.c | 28 +++++++++++++---------------
 1 file changed, 13 insertions(+), 15 deletions(-)

diff --git a/drivers/mmc/core/block.c b/drivers/mmc/core/block.c
index ce89611a136e..8db72cba2bbe 100644
--- a/drivers/mmc/core/block.c
+++ b/drivers/mmc/core/block.c
@@ -991,29 +991,27 @@ static int mmc_blk_reset(struct mmc_blk_data *md, struct mmc_host *host,
 			 int type)
 {
 	int err;
+	struct mmc_blk_data *main_md = dev_get_drvdata(&host->card->dev);
+	int part_err;
 
 	if (md->reset_done & type)
 		return -EEXIST;
 
 	md->reset_done |= type;
 	err = mmc_hw_reset(host->card);
+	if (err)
+		return err;
 	/* Ensure we switch back to the correct partition */
-	if (err) {
-		struct mmc_blk_data *main_md =
-			dev_get_drvdata(&host->card->dev);
-		int part_err;
-
-		main_md->part_curr = main_md->part_type;
-		part_err = mmc_blk_part_switch(host->card, md->part_type);
-		if (part_err) {
-			/*
-			 * We have failed to get back into the correct
-			 * partition, so we need to abort the whole request.
-			 */
-			return -ENODEV;
-		}
+	main_md->part_curr = main_md->part_type;
+	part_err = mmc_blk_part_switch(host->card, md->part_type);
+	if (part_err) {
+		/*
+		 * We have failed to get back into the correct
+		 * partition, so we need to abort the whole request.
+		 */
+		return -ENODEV;
 	}
-	return err;
+	return 0;
 }
 
 static inline void mmc_blk_reset_success(struct mmc_blk_data *md, int type)
-- 
2.37.3

Hyperstone GmbH | Reichenaustr. 39a  | 78467 Konstanz
Managing Director: Dr. Jan Peter Berns.
Commercial register of local courts: Freiburg HRB381782

Re: [PATCHv2 1/2] mmc: block: Remove error check of hw_reset on reset

[Adrian Hunter]

On 7/10/22 18:42, Christian Löhle wrote:
> Before switching back to the right partition in mmc_blk_reset
> there used to be a check if hw_reset was even supported.
> This return value was removed, so there is no reason to check.
> 
> Fixes: fefdd3c91e0a ("mmc: core: Drop superfluous validations in mmc_hw|sw_reset()")
> Cc: stable@vger.kernel.org
> 
> Signed-off-by: Christian Loehle <cloehle@hyperstone.com>
> ---
> -v2: Do not attempt to switch partitions if reset failed
> 
>  drivers/mmc/core/block.c | 28 +++++++++++++---------------
>  1 file changed, 13 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/mmc/core/block.c b/drivers/mmc/core/block.c
> index ce89611a136e..8db72cba2bbe 100644
> --- a/drivers/mmc/core/block.c
> +++ b/drivers/mmc/core/block.c
> @@ -991,29 +991,27 @@ static int mmc_blk_reset(struct mmc_blk_data *md, struct mmc_host *host,
>  			 int type)
>  {
>  	int err;
> +	struct mmc_blk_data *main_md = dev_get_drvdata(&host->card->dev);
> +	int part_err;
>  
>  	if (md->reset_done & type)
>  		return -EEXIST;
>  
>  	md->reset_done |= type;
>  	err = mmc_hw_reset(host->card);
> +	if (err)
> +		return err;

This could be a potential source of data corruption.

There is no guarantee that a subsequent I/O will fail just because
the reset failed.  Reading / writing the wrong partition would be
disastrous, so we should always try to get back to the correct
partition.

I haven't looked at the possibility of just flagging the partition
as invalid - need to be sure any subsequent I/O attempts still go
through a path that switches the partition.

>  	/* Ensure we switch back to the correct partition */
> -	if (err) {
> -		struct mmc_blk_data *main_md =
> -			dev_get_drvdata(&host->card->dev);
> -		int part_err;
> -
> -		main_md->part_curr = main_md->part_type;
> -		part_err = mmc_blk_part_switch(host->card, md->part_type);
> -		if (part_err) {
> -			/*
> -			 * We have failed to get back into the correct
> -			 * partition, so we need to abort the whole request.
> -			 */
> -			return -ENODEV;
> -		}
> +	main_md->part_curr = main_md->part_type;
> +	part_err = mmc_blk_part_switch(host->card, md->part_type);
> +	if (part_err) {
> +		/*
> +		 * We have failed to get back into the correct
> +		 * partition, so we need to abort the whole request.
> +		 */
> +		return -ENODEV;
>  	}
> -	return err;
> +	return 0;
>  }
>  
>  static inline void mmc_blk_reset_success(struct mmc_blk_data *md, int type)

RE: [PATCHv2 1/2] mmc: block: Remove error check of hw_reset on reset

[Christian Löhle]

>
>-----Original Message-----
>From: Adrian Hunter <adrian.hunter@intel.com> 
>Sent: Samstag, 8. Oktober 2022 10:38
>To: Christian Löhle <CLoehle@hyperstone.com>; Ulf Hansson <ulf.hansson@linaro.org>; Linux MMC List <linux-mmc@vger.kernel.org>; linux-kernel@vger.kernel.org
>Subject: Re: [PATCHv2 1/2] mmc: block: Remove error check of hw_reset on reset
>
>On 7/10/22 18:42, Christian Löhle wrote:
>> Before switching back to the right partition in mmc_blk_reset there 
>> used to be a check if hw_reset was even supported.
>> This return value was removed, so there is no reason to check.
>> 
>> Fixes: fefdd3c91e0a ("mmc: core: Drop superfluous validations in 
>> mmc_hw|sw_reset()")
>> Cc: stable@vger.kernel.org
>> 
>> Signed-off-by: Christian Loehle <cloehle@hyperstone.com>
>> ---
>> -v2: Do not attempt to switch partitions if reset failed
>> 
>>  drivers/mmc/core/block.c | 28 +++++++++++++---------------
>>  1 file changed, 13 insertions(+), 15 deletions(-)
>> 
>> diff --git a/drivers/mmc/core/block.c b/drivers/mmc/core/block.c index 
>> ce89611a136e..8db72cba2bbe 100644
>> --- a/drivers/mmc/core/block.c
>> +++ b/drivers/mmc/core/block.c
>> @@ -991,29 +991,27 @@ static int mmc_blk_reset(struct mmc_blk_data *md, struct mmc_host *host,
>>  			 int type)
>>  {
>>  	int err;
>> +	struct mmc_blk_data *main_md = dev_get_drvdata(&host->card->dev);
>> +	int part_err;
>>  
>>  	if (md->reset_done & type)
>>  		return -EEXIST;
>>  
>>  	md->reset_done |= type;
>>  	err = mmc_hw_reset(host->card);
>> +	if (err)
>> +		return err;
> 
> This could be a potential source of data corruption.
> 
> There is no guarantee that a subsequent I/O will fail just because the reset failed.  Reading / writing the wrong partition would be disastrous, so we should always try to get back to the correct partition.
> 
> I haven't looked at the possibility of just flagging the partition as invalid - need to be sure any subsequent I/O attempts still go through a path that switches the partition.

I can see where youre coming from, but similarly a failing mmc_blk_part_switch doesn't imply all subsequent IO will fail.
Flagging the partition as invalid can be seen as rendering the system to a potentially useless state, which is a bit overboard for e.g. one CRC7 failure on the switch.
Not sure yet what the ideal behavior is, but either way I would go with v1 1/2 and v2 2/2 for now? That already fixes imo the most relevant potential data corruptions. (successful reset -> no switch)
Then we can come up with a a good handling for mmc_blk_reset or even around mmc_blk_part_switch.
Or what do you suggest?

Regards,
Christian

Hyperstone GmbH | Reichenaustr. 39a  | 78467 Konstanz
Managing Director: Dr. Jan Peter Berns.
Commercial register of local courts: Freiburg HRB381782

Re: [PATCHv2 1/2] mmc: block: Remove error check of hw_reset on reset

[Adrian Hunter]

On 10/10/22 11:08, Christian Löhle wrote:
> 
>>
>> -----Original Message-----
>> From: Adrian Hunter <adrian.hunter@intel.com> 
>> Sent: Samstag, 8. Oktober 2022 10:38
>> To: Christian Löhle <CLoehle@hyperstone.com>; Ulf Hansson <ulf.hansson@linaro.org>; Linux MMC List <linux-mmc@vger.kernel.org>; linux-kernel@vger.kernel.org
>> Subject: Re: [PATCHv2 1/2] mmc: block: Remove error check of hw_reset on reset
>>
>> On 7/10/22 18:42, Christian Löhle wrote:
>>> Before switching back to the right partition in mmc_blk_reset there 
>>> used to be a check if hw_reset was even supported.
>>> This return value was removed, so there is no reason to check.
>>>
>>> Fixes: fefdd3c91e0a ("mmc: core: Drop superfluous validations in 
>>> mmc_hw|sw_reset()")
>>> Cc: stable@vger.kernel.org
>>>
>>> Signed-off-by: Christian Loehle <cloehle@hyperstone.com>
>>> ---
>>> -v2: Do not attempt to switch partitions if reset failed
>>>
>>>  drivers/mmc/core/block.c | 28 +++++++++++++---------------
>>>  1 file changed, 13 insertions(+), 15 deletions(-)
>>>
>>> diff --git a/drivers/mmc/core/block.c b/drivers/mmc/core/block.c index 
>>> ce89611a136e..8db72cba2bbe 100644
>>> --- a/drivers/mmc/core/block.c
>>> +++ b/drivers/mmc/core/block.c
>>> @@ -991,29 +991,27 @@ static int mmc_blk_reset(struct mmc_blk_data *md, struct mmc_host *host,
>>>  			 int type)
>>>  {
>>>  	int err;
>>> +	struct mmc_blk_data *main_md = dev_get_drvdata(&host->card->dev);
>>> +	int part_err;
>>>  
>>>  	if (md->reset_done & type)
>>>  		return -EEXIST;
>>>  
>>>  	md->reset_done |= type;
>>>  	err = mmc_hw_reset(host->card);
>>> +	if (err)
>>> +		return err;
>>
>> This could be a potential source of data corruption.
>>
>> There is no guarantee that a subsequent I/O will fail just because the reset failed.  Reading / writing the wrong partition would be disastrous, so we should always try to get back to the correct partition.
>>
>> I haven't looked at the possibility of just flagging the partition as invalid - need to be sure any subsequent I/O attempts still go through a path that switches the partition.
> 
> I can see where youre coming from, but similarly a failing mmc_blk_part_switch doesn't imply all subsequent IO will fail.
> Flagging the partition as invalid can be seen as rendering the system to a potentially useless state, which is a bit overboard for e.g. one CRC7 failure on the switch.

I wasn't clear sorry.  I meant setting main_md->part_curr to a value
that doesn't match any partition, thereby forcing the next I/O to
switch partition first.

> Not sure yet what the ideal behavior is, but either way I would go with v1 1/2 and v2 2/2 for now? That already fixes imo the most relevant potential data corruptions. (successful reset -> no switch)
> Then we can come up with a a good handling for mmc_blk_reset or even around mmc_blk_part_switch.
> Or what do you suggest?

What about what I just described above.

Re: [PATCHv2 1/2] mmc: block: Remove error check of hw_reset on reset

[Ulf Hansson]

On Mon, 10 Oct 2022 at 14:36, Adrian Hunter <adrian.hunter@intel.com> wrote:
>
> On 10/10/22 11:08, Christian Löhle wrote:
> >
> >>
> >> -----Original Message-----
> >> From: Adrian Hunter <adrian.hunter@intel.com>
> >> Sent: Samstag, 8. Oktober 2022 10:38
> >> To: Christian Löhle <CLoehle@hyperstone.com>; Ulf Hansson <ulf.hansson@linaro.org>; Linux MMC List <linux-mmc@vger.kernel.org>; linux-kernel@vger.kernel.org
> >> Subject: Re: [PATCHv2 1/2] mmc: block: Remove error check of hw_reset on reset
> >>
> >> On 7/10/22 18:42, Christian Löhle wrote:
> >>> Before switching back to the right partition in mmc_blk_reset there
> >>> used to be a check if hw_reset was even supported.
> >>> This return value was removed, so there is no reason to check.
> >>>
> >>> Fixes: fefdd3c91e0a ("mmc: core: Drop superfluous validations in
> >>> mmc_hw|sw_reset()")
> >>> Cc: stable@vger.kernel.org
> >>>
> >>> Signed-off-by: Christian Loehle <cloehle@hyperstone.com>
> >>> ---
> >>> -v2: Do not attempt to switch partitions if reset failed
> >>>
> >>>  drivers/mmc/core/block.c | 28 +++++++++++++---------------
> >>>  1 file changed, 13 insertions(+), 15 deletions(-)
> >>>
> >>> diff --git a/drivers/mmc/core/block.c b/drivers/mmc/core/block.c index
> >>> ce89611a136e..8db72cba2bbe 100644
> >>> --- a/drivers/mmc/core/block.c
> >>> +++ b/drivers/mmc/core/block.c
> >>> @@ -991,29 +991,27 @@ static int mmc_blk_reset(struct mmc_blk_data *md, struct mmc_host *host,
> >>>                      int type)
> >>>  {
> >>>     int err;
> >>> +   struct mmc_blk_data *main_md = dev_get_drvdata(&host->card->dev);
> >>> +   int part_err;
> >>>
> >>>     if (md->reset_done & type)
> >>>             return -EEXIST;
> >>>
> >>>     md->reset_done |= type;
> >>>     err = mmc_hw_reset(host->card);
> >>> +   if (err)
> >>> +           return err;
> >>
> >> This could be a potential source of data corruption.
> >>
> >> There is no guarantee that a subsequent I/O will fail just because the reset failed.  Reading / writing the wrong partition would be disastrous, so we should always try to get back to the correct partition.
> >>
> >> I haven't looked at the possibility of just flagging the partition as invalid - need to be sure any subsequent I/O attempts still go through a path that switches the partition.
> >
> > I can see where youre coming from, but similarly a failing mmc_blk_part_switch doesn't imply all subsequent IO will fail.
> > Flagging the partition as invalid can be seen as rendering the system to a potentially useless state, which is a bit overboard for e.g. one CRC7 failure on the switch.
>
> I wasn't clear sorry.  I meant setting main_md->part_curr to a value
> that doesn't match any partition, thereby forcing the next I/O to
> switch partition first.

If I understand correctly, you are suggesting to ignore the return
code from mmc_hw_reset() and then always try to switch to the correct
partition. If we end up failing to switch the partition, then we
should set an invalid value in main_md->part_curr and return an error
code?

>
> > Not sure yet what the ideal behavior is, but either way I would go with v1 1/2 and v2 2/2 for now? That already fixes imo the most relevant potential data corruptions. (successful reset -> no switch)
> > Then we can come up with a a good handling for mmc_blk_reset or even around mmc_blk_part_switch.
> > Or what do you suggest?
>
> What about what I just described above.
>

It seems reasonable to me (assuming I have understood correctly).

One additional thing though. I would appreciate some comments in the
code, so it becomes clear of what goes on.

Kind regards
Uffe