[PATCH 5.0 064/238] mmc:fix a bug when max_discard is 0

[Greg Kroah-Hartman]

5.0-stable review patch.  If anyone has any objections, please let me know.

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

From: Jiong Wu <lohengrin1024@xxxxxxxxx>

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@xxxxxxxxx>
Fixes: b305882fbc87 (mmc: core: optimize mmc_calc_max_discard)
Cc: stable@xxxxxxxxxxxxxxx # v4.17+
Signed-off-by: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 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;