[PATCH AUTOSEL 4.19 51/60] md: fix for divide error in status_resync

Sasha Levin
2019-06-27T00:39:03Z

From: Mariusz Tkaczyk <mariusz.tkaczyk@intel.com>

[ Upstream commit 9642fa73d073527b0cbc337cc17a47d545d82cd2 ]

Stopping external metadata arrays during resync/recovery causes
retries, loop of interrupting and starting reconstruction, until it
hit at good moment to stop completely. While these retries
curr_mark_cnt can be small- especially on HDD drives, so subtraction
result can be smaller than 0. However it is casted to uint without
checking. As a result of it the status bar in /proc/mdstat while stopping
is strange (it jumps between 0% and 99%).

The real problem occurs here after commit 72deb455b5ec ("block: remove
CONFIG_LBDAF"). Sector_div() macro has been changed, now the
divisor is casted to uint32. For db = -8 the divisior(db/32-1) becomes 0.

Check if db value can be really counted and replace these macro by
div64_u64() inline.

Signed-off-by: Mariusz Tkaczyk <mariusz.tkaczyk@intel.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/md/md.c | 36 ++++++++++++++++++++++--------------
1 file changed, 22 insertions(+), 14 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index b924f62e2cd5..fb5d702e43b5 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -7625,9 +7625,9 @@ static void status_unused(struct seq_file *seq)
static int status_resync(struct seq_file *seq, struct mddev *mddev)
{
sector_t max_sectors, resync, res;
- unsigned long dt, db;
- sector_t rt;
- int scale;
+ unsigned long dt, db = 0;
+ sector_t rt, curr_mark_cnt, resync_mark_cnt;
+ int scale, recovery_active;
unsigned int per_milli;

if (test_bit(MD_RECOVERY_SYNC, &mddev->recovery) ||
@@ -7716,22 +7716,30 @@ static int status_resync(struct seq_file *seq, struct mddev *mddev)
* db: blocks written from mark until now
* rt: remaining time
*
- * rt is a sector_t, so could be 32bit or 64bit.
- * So we divide before multiply in case it is 32bit and close
- * to the limit.
- * We scale the divisor (db) by 32 to avoid losing precision
- * near the end of resync when the number of remaining sectors
- * is close to 'db'.
- * We then divide rt by 32 after multiplying by db to compensate.
- * The '+1' avoids division by zero if db is very small.
+ * rt is a sector_t, which is always 64bit now. We are keeping
+ * the original algorithm, but it is not really necessary.
+ *
+ * Original algorithm:
+ * So we divide before multiply in case it is 32bit and close
+ * to the limit.
+ * We scale the divisor (db) by 32 to avoid losing precision
+ * near the end of resync when the number of remaining sectors
+ * is close to 'db'.
+ * We then divide rt by 32 after multiplying by db to compensate.
+ * The '+1' avoids division by zero if db is very small.
*/
dt = ((jiffies - mddev->resync_mark) / HZ);
if (!dt) dt++;
- db = (mddev->curr_mark_cnt - atomic_read(&mddev->recovery_active))
- - mddev->resync_mark_cnt;
+
+ curr_mark_cnt = mddev->curr_mark_cnt;
+ recovery_active = atomic_read(&mddev->recovery_active);
+ resync_mark_cnt = mddev->resync_mark_cnt;
+
+ if (curr_mark_cnt >= (recovery_active + resync_mark_cnt))
+ db = curr_mark_cnt - (recovery_active + resync_mark_cnt);

rt = max_sectors - resync; /* number of remaining sectors */
- sector_div(rt, db/32+1);
+ rt = div64_u64(rt, db/32+1);
rt *= dt;
rt >>= 5;

--
2.20.1