linux-kernel - [PATCH] btrfs: fix return value when race occur between balance and cancel/pause

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Date:   Wed,  9 Aug 2023 23:48:10 -0400
From:   xiaoshoukui <xiaoshoukui@...il.com>
To:     josef@...icpanda.com, dsterba@...e.com, clm@...com
Cc:     linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        xiaoshoukui <xiaoshoukui@...il.com>,
        xiaoshoukui <xiaoshoukui@...jie.com.cn>
Subject: [PATCH] btrfs: fix return value when race occur between balance and cancel/pause

Issue a pause or cancel IOCTL request after judging that there is no
pause or cancel request on the path of __btrfs_balance to return 0,
which will mislead the user that the pause or cancel requests are
successful.In fact, the balance request has not been paused or canceled.

On that race condition, a non-zero errno should be returned to the user.

Signed-off-by: xiaoshoukui <xiaoshoukui@...jie.com.cn>
---
 fs/btrfs/fs.h      |  6 ++++++
 fs/btrfs/volumes.c | 14 +++++++++-----
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/fs/btrfs/fs.h b/fs/btrfs/fs.h
index 203d2a267828..c27def881922 100644
--- a/fs/btrfs/fs.h
+++ b/fs/btrfs/fs.h
@@ -93,6 +93,12 @@ enum {
 	 */
 	BTRFS_FS_BALANCE_RUNNING,
 
+	/* Indicate that balance has been paused. */
+	BTRFS_FS_BALANCE_PAUSED,
+
+	/* Indicate that balance has been canceled. */
+	BTRFS_FS_BALANCE_CANCELED,
+
 	/*
 	 * Indicate that relocation of a chunk has started, it's set per chunk
 	 * and is toggled between chunks.
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 2ecb76cf3d91..839ce1808f23 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -4267,7 +4267,6 @@ int btrfs_balance(struct btrfs_fs_info *fs_info,
 	u64 num_devices;
 	unsigned seq;
 	bool reducing_redundancy;
-	bool paused = false;
 	int i;
 
 	if (btrfs_fs_closing(fs_info) ||
@@ -4390,6 +4389,8 @@ int btrfs_balance(struct btrfs_fs_info *fs_info,
 	ASSERT(!test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags));
 	set_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags);
 	describe_balance_start_or_resume(fs_info);
+	clear_bit(BTRFS_FS_BALANCE_PAUSED, &fs_info->flags);
+	clear_bit(BTRFS_FS_BALANCE_CANCELED, &fs_info->flags);
 	mutex_unlock(&fs_info->balance_mutex);
 
 	ret = __btrfs_balance(fs_info);
@@ -4398,7 +4399,7 @@ int btrfs_balance(struct btrfs_fs_info *fs_info,
 	if (ret == -ECANCELED && atomic_read(&fs_info->balance_pause_req)) {
 		btrfs_info(fs_info, "balance: paused");
 		btrfs_exclop_balance(fs_info, BTRFS_EXCLOP_BALANCE_PAUSED);
-		paused = true;
+		set_bit(BTRFS_FS_BALANCE_PAUSED, &fs_info->flags);
 	}
 	/*
 	 * Balance can be canceled by:
@@ -4415,8 +4416,10 @@ int btrfs_balance(struct btrfs_fs_info *fs_info,
 	 *
 	 * So here we only check the return value to catch canceled balance.
 	 */
-	else if (ret == -ECANCELED || ret == -EINTR)
+	else if (ret == -ECANCELED || ret == -EINTR) {
 		btrfs_info(fs_info, "balance: canceled");
+		set_bit(BTRFS_FS_BALANCE_CANCELED, &fs_info->flags);
+	}
 	else
 		btrfs_info(fs_info, "balance: ended with status: %d", ret);
 
@@ -4428,7 +4431,7 @@ int btrfs_balance(struct btrfs_fs_info *fs_info,
 	}
 
 	/* We didn't pause, we can clean everything up. */
-	if (!paused) {
+	if (!test_bit(BTRFS_FS_BALANCE_PAUSED, &fs_info->flags)) {
 		reset_balance_state(fs_info);
 		btrfs_exclop_finish(fs_info);
 	}
@@ -4587,6 +4590,7 @@ int btrfs_pause_balance(struct btrfs_fs_info *fs_info)
 		/* we are good with balance_ctl ripped off from under us */
 		BUG_ON(test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags));
 		atomic_dec(&fs_info->balance_pause_req);
+		ret = test_bit(BTRFS_FS_BALANCE_PAUSED, &fs_info->flags) ? 0 : -EINVAL;
 	} else {
 		ret = -ENOTCONN;
 	}
@@ -4642,7 +4646,7 @@ int btrfs_cancel_balance(struct btrfs_fs_info *fs_info)
 		test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags));
 	atomic_dec(&fs_info->balance_cancel_req);
 	mutex_unlock(&fs_info->balance_mutex);
-	return 0;
+	return test_bit(BTRFS_FS_BALANCE_CANCELED, &fs_info->flags) ? 0 : -EINVAL;
 }
 
 int btrfs_uuid_scan_kthread(void *data)
-- 
2.20.1