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md: fix for divide error in status_resync

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[ 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>
This commit is contained in:
Mariusz Tkaczyk 2019-06-13 16:11:41 +02:00 committed by Greg Kroah-Hartman
parent 44aa12109c
commit 50e8a09f55
1 changed files with 22 additions and 14 deletions
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36
drivers/md/md.c
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@ -7226,9 +7226,9 @@ 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) ||
@ -7298,22 +7298,30 @@ 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;