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

[Peter Collingbourne <pcc@google.com>]

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.

Peter