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    Subject[PATCH 5.0 064/238] mmc:fix a bug when max_discard is 0
    Date
    5.0-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Jiong Wu <lohengrin1024@gmail.com>

    commit d4721339dcca7def04909a8e60da43c19a24d8bf upstream.

    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@gmail.com>
    Fixes: b305882fbc87 (mmc: core: optimize mmc_calc_max_discard)
    Cc: stable@vger.kernel.org # v4.17+
    Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/mmc/core/core.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    --- a/drivers/mmc/core/core.c
    +++ b/drivers/mmc/core/core.c
    @@ -2381,9 +2381,9 @@ unsigned int mmc_calc_max_discard(struct
    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;

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