mmc:fix a bug when max_discard is 0

Commit Message

Jiong Wu Feb. 28, 2019, 4:18 p.m. UTC

From: Jiong Wu <[e-mail]>

The original purpose of the code I fix is to replace max_discard with
max_trim if max_trim is less than max_discard. When max_discard is 0
we should replace max_discard with max_trim as well, because
max_discard equals 0 happens only when the max_do_calc_max_discard
process is overflowed, so if mmc_can_trim(card) is true, max_discard
should be replaced by an available max_trim.
However, in the original code, there are two lines of code interfere
the right process.
1) if (max_discard && mmc_can_trim(card))
when max_discard is 0, it skips the process checking if max_discard
needs to be replaced with max_trim.
2) if (max_trim < max_discard)
the condition is false when max_discard is 0. it also skips the process
that replaces max_discard with max_trim, in fact, we should replace the
0-valued max_discard with max_trim.

Signed-off-by: Jiong Wu <[e-mail]>
---
 drivers/mmc/core/core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Comments

Ulf Hansson March 1, 2019, 8:51 a.m. UTC | #1

On Thu, 28 Feb 2019 at 17:19, Jiong Wu <[e-mail]> wrote:
>
> From: Jiong Wu <[e-mail]>
>
> The original purpose of the code I fix is to replace max_discard with
> max_trim if max_trim is less than max_discard. When max_discard is 0
> we should replace max_discard with max_trim as well, because
> max_discard equals 0 happens only when the max_do_calc_max_discard
> process is overflowed, so if mmc_can_trim(card) is true, max_discard
> should be replaced by an available max_trim.
> However, in the original code, there are two lines of code interfere
> the right process.
> 1) if (max_discard && mmc_can_trim(card))
> when max_discard is 0, it skips the process checking if max_discard
> needs to be replaced with max_trim.
> 2) if (max_trim < max_discard)
> the condition is false when max_discard is 0. it also skips the process
> that replaces max_discard with max_trim, in fact, we should replace the
> 0-valued max_discard with max_trim.
>
> Signed-off-by: Jiong Wu <[e-mail]>

Yes, this makes sense to me now. However, it's too late for me to pick
this a fix for 5.0, but I have queued it for 5.1 and added the
following tags:

Fixes: b305882fbc87 (mmc: core: optimize mmc_calc_max_discard)
Cc: [e-mail] # v4.17+

If you want to patch older kernels and manual backport needs to be
submitted to stable.

Thanks and kind regards
Uffe

> ---
>  drivers/mmc/core/core.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> index 5bd58b9..caaefc0 100644
> --- a/drivers/mmc/core/core.c
> +++ b/drivers/mmc/core/core.c
> @@ -2381,9 +2381,9 @@ unsigned int mmc_calc_max_discard(struct mmc_card *card)
>                 return card->pref_erase;
>
>         max_discard = mmc_do_calc_max_discard(card, MMC_ERASE_ARG);
> -       if (max_discard && mmc_can_trim(card)) {
> +       if (mmc_can_trim(card)) {
>                 max_trim = mmc_do_calc_max_discard(card, MMC_TRIM_ARG);
> -               if (max_trim < max_discard)
> +               if (max_trim < max_discard || max_discard == 0)
>                         max_discard = max_trim;
>         } else if (max_discard < card->erase_size) {
>                 max_discard = 0;
> --
> 2.7.4
>

Patch

diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index 5bd58b9..caaefc0 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -2381,9 +2381,9 @@  unsigned int mmc_calc_max_discard(struct mmc_card *card)
 		return card->pref_erase;
 
 	max_discard = mmc_do_calc_max_discard(card, MMC_ERASE_ARG);
-	if (max_discard && mmc_can_trim(card)) {
+	if (mmc_can_trim(card)) {
 		max_trim = mmc_do_calc_max_discard(card, MMC_TRIM_ARG);
-		if (max_trim < max_discard)
+		if (max_trim < max_discard || max_discard == 0)
 			max_discard = max_trim;
 	} else if (max_discard < card->erase_size) {
 		max_discard = 0;