[PATCH 6/6] md/raid5: Don't check crossing reshape when reshape hasn't started

[Xiao Ni <xni@redhat.com>]

stripe_ahead_of_reshape is used to check if a stripe region cross the
reshape position. So first, change the function name to
stripe_across_reshape to describe the usage of this function.

For reshape backwards, it starts reshape from the end of array and conf->
reshape_progress is init to raid5_size. During reshape, if previous is true
(set in make_stripe_request) and max_sector >= conf->reshape_progress, ios
should wait until reshape window moves forward. But ios don't need to wait
if max_sector is raid5_size.

And put the conditions into the function directly to make understand the
codes easily.

This can be reproduced easily by lvm2 test shell/lvconvert-raid-reshape.sh
For dm raid reshape, before starting sync thread, it needs to reload table
some times. In one time dm raid uses MD_RECOVERY_WAIT to delay reshape and
it doesn't start sync thread this time. Then one io comes in and it waits
because stripe_ahead_of_reshape returns true because it's a backward
reshape and max_sectors > conf->reshape_progress. But the reshape hasn't
started. So skip this check when reshape_progress is raid5_size

Fixes: 486f60558607 ("md/raid5: Check all disks in a stripe_head for reshape progress")
Signed-off-by: Xiao Ni <xni@redhat.com>
---
 drivers/md/raid5.c | 22 ++++++++++------------
 1 file changed, 10 insertions(+), 12 deletions(-)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 8497880135ee..965991a3104f 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -5832,17 +5832,12 @@ static bool ahead_of_reshape(struct mddev *mddev, sector_t sector,
 					  sector >= reshape_sector;
 }
 
-static bool range_ahead_of_reshape(struct mddev *mddev, sector_t min,
-				   sector_t max, sector_t reshape_sector)
-{
-	return mddev->reshape_backwards ? max < reshape_sector :
-					  min >= reshape_sector;
-}
-
-static bool stripe_ahead_of_reshape(struct mddev *mddev, struct r5conf *conf,
+static sector_t raid5_size(struct mddev *mddev, sector_t sectors, int raid_disks);
+static bool stripe_across_reshape(struct mddev *mddev, struct r5conf *conf,
 				    struct stripe_head *sh)
 {
 	sector_t max_sector = 0, min_sector = MaxSector;
+	sector_t reshape_pos = 0;
 	bool ret = false;
 	int dd_idx;
 
@@ -5856,9 +5851,12 @@ static bool stripe_ahead_of_reshape(struct mddev *mddev, struct r5conf *conf,
 
 	spin_lock_irq(&conf->device_lock);
 
-	if (!range_ahead_of_reshape(mddev, min_sector, max_sector,
-				     conf->reshape_progress))
-		/* mismatch, need to try again */
+	reshape_pos = conf->reshape_progress;
+	if (mddev->reshape_backwards) {
+		if (max_sector >= reshape_pos &&
+		    reshape_pos != raid5_size(mddev, 0, 0))
+			ret = true;
+	} else if (min_sector < reshape_pos)
 		ret = true;
 
 	spin_unlock_irq(&conf->device_lock);
@@ -5969,7 +5967,7 @@ static enum stripe_result make_stripe_request(struct mddev *mddev,
 	}
 
 	if (unlikely(previous) &&
-	    stripe_ahead_of_reshape(mddev, conf, sh)) {
+	    stripe_across_reshape(mddev, conf, sh)) {
 		/*
 		 * Expansion moved on while waiting for a stripe.
 		 * Expansion could still move past after this
-- 
2.32.0 (Apple Git-132)