[PATCH 0/2] btrfs: Fix out-of-space bug

[Zhaolei <zhaolei@cn.fujitsu.com>]

From: Zhao Lei <zhaolei@cn.fujitsu.com>

Btrfs will report NO_SPACE when we create and remove files for several times:
1: Create a single-dev btrfs fs with default option
2: Write a file into it to take up most fs space
3: Delete above file
4: Wait about 100s to let chunk removed
5: goto 2

Script is like following:
 #!/bin/bash

 # Recommend 1.2G space, too large disk will make test slow
 DEV="/dev/sda16"
 MNT="/mnt/tmp"

 dev_size="$(lsblk -bn -o SIZE "$DEV")" || exit 2
 file_size_m=$((dev_size * 75 / 100 / 1024 / 1024))

 echo "Loop write ${file_size_m}M file on $((dev_size / 1024 / 1024))M dev"

 for ((i = 0; i < 10; i++)); do umount "$MNT" 2>/dev/null; done
 echo "mkfs $DEV"
 mkfs.btrfs -f "$DEV" >/dev/null || exit 2
 echo "mount $DEV $MNT"
 mount "$DEV" "$MNT" || exit 2

 for ((loop_i = 0; loop_i < 20; loop_i++)); do
     echo
     echo "loop $loop_i"

     echo "dd file..."
     cmd=(dd if=/dev/zero of="$MNT"/file0 bs=1M count="$file_size_m")
     "${cmd[@]}" 2>/dev/null || {
         # NO_SPACE error triggered
         echo "dd failed: ${cmd[*]}"
         exit 1
     }

     echo "rm file..."
     rm -f "$MNT"/file0 || exit 2

     for ((i = 0; i < 10; i++)); do
         df "$MNT" | tail -1
         sleep 10
     done
 done

Reason:
It is triggered by commit: 47ab2a6c689913db23ccae38349714edf8365e0a
which is used to remove empty block groups automatically, but the
reason is not in that patch. Code before works well because btrfs
don't need to create and delete chunks so many times and with high
complexity.

Reason1:
 Btrfs get free disk space by calling find_free_dev_extent() when
 re-create chunk for write, but current code set search_commit_root
 flag in searching tree, so disk spaces which was freed from dev_tree
 but not commited can not get from find_free_dev_extent(), then
 btrfs report NO_SPACE on above case.
 Fixed in patch 1/2.

Reason2:
 When we remove some continuous chunks but leave other chunks after,
 these disk space should be used by chunk-recreating, but in current
 code, only first create will successed.
 Fixed in patch 2/2.

Reason3:
 contains_pending_extent() return wrong value in calculation.
 Fixed by Forrest Liu <forrestl@synology.com> in:
 Btrfs: fix find_free_dev_extent() malfunction in case device tree has hole

Tested by above script, and confirmed action with many printk.

Reported-by: Tsutomu Itoh <t-itoh@jp.fujitsu.com>

Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>

Zhao Lei (2):
  btrfs: Fix out-of-space bug caused by searching commit_root in
    find_free_dev_extent()
  btrfs: Set hole_size to free space in case of contains_pending_extent

 fs/btrfs/volumes.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

-- 
1.8.5.1