We are facing the same problem with EDQUOT which was experienced with
ENOSPC. Not sure if we require a full ticketing system such as ENOSPC, but
here is a quick fix, which may be too big a hammer.

Quotas are reserved during the start of an operation, incrementing
qg->reserved. However, it is written to disk in a commit_transaction
which could take as long as commit_interval. In the meantime there
could be deletions which are not accounted for because deletions are
accounted for only while committed (free_refroot). So, when we get
a EDQUOT flush the data to disk and try again.

This fixes fstests btrfs/139.

Here is a sample script which shows this issue.

DEVICE=/dev/vdb
MOUNTPOINT=/mnt
TESTVOL=$MOUNTPOINT/tmp
QUOTA=5
PROG=btrfs
DD_BS="4k"
DD_COUNT="256"
RUN_TIMES=5000

mkfs.btrfs -f $DEVICE
mount -o commit=240 $DEVICE $MOUNTPOINT
$PROG subvolume create $TESTVOL
$PROG quota enable $TESTVOL
$PROG qgroup limit ${QUOTA}G $TESTVOL

typeset -i DD_RUN_GOOD
typeset -i QUOTA

function _check_cmd() {
        if [[ ${?} > 0 ]]; then
                echo -n "$(date) E: Running previous command"
                echo ${*}
                echo "Without sync"
                $PROG qgroup show -pcreFf ${TESTVOL}
                echo "With sync"
                $PROG qgroup show -pcreFf --sync ${TESTVOL}
                exit 1
        fi
}

while true; do
  DD_RUN_GOOD=$RUN_TIMES

  while (( ${DD_RUN_GOOD} != 0 )); do
        dd if=/dev/zero of=${TESTVOL}/quotatest${DD_RUN_GOOD} bs=${DD_BS} count=${DD_COUNT}
        _check_cmd "dd if=/dev/zero of=${TESTVOL}/quotatest${DD_RUN_GOOD} bs=${DD_BS} count=${DD_COUNT}"
        DD_RUN_GOOD=(${DD_RUN_GOOD}-1)
  done

  $PROG qgroup show -pcref $TESTVOL
  echo "----------- Cleanup ---------- "
  rm $TESTVOL/quotatest*

done
Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
Reviewed-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>