linux-kernel - [PATCH AUTOSEL 5.10 10/51] btrfs: fix async discard stall

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Message-Id: <20210112125534.70280-10-sashal@kernel.org>
Date:   Tue, 12 Jan 2021 07:54:52 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Pavel Begunkov <asml.silence@...il.com>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>,
        Sasha Levin <sashal@...nel.org>, linux-btrfs@...r.kernel.org
Subject: [PATCH AUTOSEL 5.10 10/51] btrfs: fix async discard stall

From: Pavel Begunkov <asml.silence@...il.com>

[ Upstream commit ea9ed87c73e87e044b2c58d658eb4ba5216bc488 ]

Might happen that bg->discard_eligible_time was changed without
rescheduling, so btrfs_discard_workfn() wakes up earlier than that new
time, peek_discard_list() returns NULL, and all work halts and goes to
sleep without further rescheduling even there are block groups to
discard.

It happens pretty often, but not so visible from the userspace because
after some time it usually will be kicked off anyway by someone else
calling btrfs_discard_reschedule_work().

Fix it by continue rescheduling if block group discard lists are not
empty.

Reviewed-by: Josef Bacik <josef@...icpanda.com>
Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
Signed-off-by: David Sterba <dsterba@...e.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/btrfs/discard.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/fs/btrfs/discard.c b/fs/btrfs/discard.c
index 741c7e19c32f2..d1a5380e8827d 100644
--- a/fs/btrfs/discard.c
+++ b/fs/btrfs/discard.c
@@ -199,16 +199,15 @@ static struct btrfs_block_group *find_next_block_group(
 static struct btrfs_block_group *peek_discard_list(
 					struct btrfs_discard_ctl *discard_ctl,
 					enum btrfs_discard_state *discard_state,
-					int *discard_index)
+					int *discard_index, u64 now)
 {
 	struct btrfs_block_group *block_group;
-	const u64 now = ktime_get_ns();
 
 	spin_lock(&discard_ctl->lock);
 again:
 	block_group = find_next_block_group(discard_ctl, now);
 
-	if (block_group && now > block_group->discard_eligible_time) {
+	if (block_group && now >= block_group->discard_eligible_time) {
 		if (block_group->discard_index == BTRFS_DISCARD_INDEX_UNUSED &&
 		    block_group->used != 0) {
 			if (btrfs_is_block_group_data_only(block_group))
@@ -222,12 +221,11 @@ static struct btrfs_block_group *peek_discard_list(
 			block_group->discard_state = BTRFS_DISCARD_EXTENTS;
 		}
 		discard_ctl->block_group = block_group;
+	}
+	if (block_group) {
 		*discard_state = block_group->discard_state;
 		*discard_index = block_group->discard_index;
-	} else {
-		block_group = NULL;
 	}
-
 	spin_unlock(&discard_ctl->lock);
 
 	return block_group;
@@ -429,13 +427,18 @@ static void btrfs_discard_workfn(struct work_struct *work)
 	int discard_index = 0;
 	u64 trimmed = 0;
 	u64 minlen = 0;
+	u64 now = ktime_get_ns();
 
 	discard_ctl = container_of(work, struct btrfs_discard_ctl, work.work);
 
 	block_group = peek_discard_list(discard_ctl, &discard_state,
-					&discard_index);
+					&discard_index, now);
 	if (!block_group || !btrfs_run_discard_work(discard_ctl))
 		return;
+	if (now < block_group->discard_eligible_time) {
+		btrfs_discard_schedule_work(discard_ctl, false);
+		return;
+	}
 
 	/* Perform discarding */
 	minlen = discard_minlen[discard_index];
-- 
2.27.0