On Thu, 28 Feb 2019 at 17:19, Jiong Wu <lohengrin1024@xxxxxxxxx> wrote:
>
> From: Jiong Wu <lohengrin1024@xxxxxxxxx>
>
> 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 <Lohengrin1024@xxxxxxxxx>
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: stable@xxxxxxxxxxxxxxx # 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
>
