Re: [PATCH] mmc: core: don't initialize block size from ext_csd if not present

[Adrian Hunter <adrian.hunter@intel.com>]

On 13/01/21 9:46 pm, Peter Collingbourne wrote:
> On Wed, Jan 13, 2021 at 2:43 AM Adrian Hunter <adrian.hunter@intel.com> wrote:
>>
>> On 12/01/21 11:09 pm, Peter Collingbourne wrote:
>>> If extended CSD was not available, the eMMC driver would incorrectly
>>> set the block size to 0, as the data_sector_size field of ext_csd
>>> was never initialized. This issue was exposed by commit 817046ecddbc
>>> ("block: Align max_hw_sectors to logical blocksize") which caused
>>> max_sectors and max_hw_sectors to be set to 0 after setting the block
>>> size to 0, resulting in a kernel panic in bio_split when attempting
>>> to read from the device. Fix it by only reading the block size from
>>> ext_csd if it is available.
>>>
>>> Fixes: 817046ecddbc ("block: Align max_hw_sectors to logical blocksize")
>>
>> I would go with the original commit i.e.
>>
>> Fixes: a5075eb94837 ("mmc: block: Allow disabling 512B sector size emulation")
> 
> Sure, makes sense.
> 
>>> Signed-off-by: Peter Collingbourne <pcc@google.com>
>>> Link: https://linux-review.googlesource.com/id/If244d178da4d86b52034459438fec295b02d6e60
>>> ---
>>>  drivers/mmc/core/queue.c | 3 ++-
>>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/mmc/core/queue.c b/drivers/mmc/core/queue.c
>>> index de7cb0369c30..735cdbf1145c 100644
>>> --- a/drivers/mmc/core/queue.c
>>> +++ b/drivers/mmc/core/queue.c
>>> @@ -20,6 +20,7 @@
>>>  #include "core.h"
>>>  #include "card.h"
>>>  #include "host.h"
>>> +#include "mmc_ops.h"
>>>
>>>  #define MMC_DMA_MAP_MERGE_SEGMENTS   512
>>>
>>> @@ -384,7 +385,7 @@ static void mmc_setup_queue(struct mmc_queue *mq, struct mmc_card *card)
>>>                    "merging was advertised but not possible");
>>>       blk_queue_max_segments(mq->queue, mmc_get_max_segments(host));
>>>
>>> -     if (mmc_card_mmc(card))
>>> +     if (mmc_card_mmc(card) && mmc_can_ext_csd(card))
>>>               block_size = card->ext_csd.data_sector_size;
>>
>> Might as well be:
>>
>>         if (mmc_card_mmc(card) && card->ext_csd.data_sector_size)
>>                 block_size = card->ext_csd.data_sector_size;
> 
> Can we rely on this data structure to be zero initialized? I suppose
> so, provided that it was allocated with mmc_alloc_card which uses
> kzalloc. But it isn't entirely obvious and I figure it may be a little
> better to be explicit in our intent here. But either way works for me.

The only valid values are 512 and 4096, so you could add WARN_ON(block_size
!= 512 && block_size != 4096) if you want.