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@xxxxxxxxx> 
>> Sent: Samstag, 8. Oktober 2022 10:38
>> To: Christian Löhle <CLoehle@xxxxxxxxxxxxxx>; Ulf Hansson <ulf.hansson@xxxxxxxxxx>; Linux MMC List <linux-mmc@xxxxxxxxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx
>> 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@xxxxxxxxxxxxxxx
>>>
>>> Signed-off-by: Christian Loehle <cloehle@xxxxxxxxxxxxxx>
>>> ---
>>> -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.