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

On Wed, Jan 13, 2021 at 10:11 PM Adrian Hunter [off-list ref] wrote:

On 13/01/21 9:46 pm, Peter Collingbourne wrote:

quoted

On Wed, Jan 13, 2021 at 2:43 AM Adrian Hunter [off-list ref] wrote:

quoted

On 12/01/21 11:09 pm, Peter Collingbourne wrote:

quoted

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.

quoted

quoted

Signed-off-by: Peter Collingbourne <redacted>
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.

Okay, I did that in v2.

Peter