FAILED: patch "[PATCH] btrfs: fix qgroup data rsv leak caused by falloc failure" failed to apply to 5.11-stable tree

The patch below does not apply to the 5.11-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From a3ee79bd8fe17812d2305ccc4bf81bfeab395576 Mon Sep 17 00:00:00 2001
From: Qu Wenruo <[email protected]>
Date: Wed, 3 Mar 2021 18:41:52 +0800
Subject: [PATCH] btrfs: fix qgroup data rsv leak caused by falloc failure

[BUG]
When running fsstress with only falloc workload, and a very low qgroup limit set, we can get qgroup data rsv leak at unmount time.

BTRFS warning (device dm-0): qgroup 0/5 has unreleased space, type 0 rsv 20480 BTRFS error (device dm-0): qgroup reserved space leaked

The minimal reproducer looks like:

#!/bin/bash
dev=/dev/test/test
mnt="/mnt/btrfs"
fsstress=~/xfstests-dev/ltp/fsstress
runtime=8

  workload()
  {
          umount $dev &> /dev/null
          umount $mnt &> /dev/null
          mkfs.btrfs -f $dev > /dev/null
          mount $dev $mnt

btrfs quota en $mnt
btrfs quota rescan -w $mnt
btrfs qgroup limit 16m 0/5 $mnt

$fsstress -w -z -f creat=10 -f fallocate=10 -p 2 -n 100 \
-d $mnt -v > /tmp/fsstress

umount $mnt
if dmesg | grep leak ; then
echo "!!! FAILED !!!"
exit 1
fi
}

for (( i=0; i < $runtime; i++)); do

          echo "=== $i/$runtime==="
          workload

done

Normally it would fail before round 4.

[CAUSE]
In function insert_prealloc_file_extent(), we first call btrfs_qgroup_release_data() to know how many bytes are reserved for qgroup data rsv.

Then use that @qgroup_released number to continue our work.

But after we call btrfs_qgroup_release_data(), we should either queue @qgroup_released to delayed ref or free them manually in error path.

Unfortunately, we lack the error handling to free the released bytes, leaking qgroup data rsv.

All the error handling function outside won't help at all, as we have released the range, meaning in inode io tree, the EXTENT_QGROUP_RESERVED bit is already cleared, thus all btrfs_qgroup_free_data() call won't free any data rsv.

[FIX]
Add free_qgroup tag to manually free the released qgroup data rsv.

index 77182be403c5..ea5ede619220 100644
@@ -9895,7 +9895,7 @@ static struct btrfs_trans_handle *insert_prealloc_file_extent(
 						  file_offset, &stack_fi,
 						  true, qgroup_released);
 		if (ret)
-			return ERR_PTR(ret);
+			goto free_qgroup;
 		return trans;
 	}
 

@@ -9910,17 +9910,31 @@ static struct btrfs_trans_handle *insert_prealloc_file_extent(
 	extent_info.insertions = 0;
 
 	path = btrfs_alloc_path();
-	if (!path)
-		return ERR_PTR(-ENOMEM);
+	if (!path) {
+		ret = -ENOMEM;
+		goto free_qgroup;
+	}
 
 	ret = btrfs_replace_file_extents(&inode->vfs_inode, path, file_offset,
 				     file_offset + len - 1, &extent_info,
 				     &trans);
 	btrfs_free_path(path);
 	if (ret)
-		return ERR_PTR(ret);
-
+		goto free_qgroup;
 	return trans;
+
+free_qgroup:
+	/*
+	 * We have released qgroup data range at the beginning of the function,
+	 * and normally qgroup_released bytes will be freed when committing
+	 * transaction.
+	 * But if we error out early, we have to free what we have released
+	 * or we leak qgroup data reservation.
+	 */
+	btrfs_qgroup_free_refroot(inode->root->fs_info,
+			inode->root->root_key.objectid, qgroup_released,
+			BTRFS_QGROUP_RSV_DATA);
+	return ERR_PTR(ret);
 }
 
 static int __btrfs_prealloc_file_range(struct inode *inode, int mode,