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

[Christian Löhle]

>
>-----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.
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

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