6.16-stable review patch. If anyone has any objections, please let me know.
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From: Boris Burkov boris@bur.io
commit 7b632596188e1973c6b3ac1c9f8252f735e1039f upstream.
__qgroup_excl_accounting() uses the qgroup iterator machinery to update the account of one qgroups usage for all its parent hierarchy, when we either add or remove a relation and have only exclusive usage.
However, there is a small bug there: we loop with an extra iteration temporary qgroup called `cur` but never actually refer to that in the body of the loop. As a result, we redundantly account the same usage to the first qgroup in the list.
This can be reproduced in the following way:
mkfs.btrfs -f -O squota <dev> mount <dev> <mnt> btrfs subvol create <mnt>/sv dd if=/dev/zero of=<mnt>/sv/f bs=1M count=1 sync btrfs qgroup create 1/100 <mnt> btrfs qgroup create 2/200 <mnt> btrfs qgroup assign 1/100 2/200 <mnt> btrfs qgroup assign 0/256 1/100 <mnt> btrfs qgroup show <mnt>
and the broken result is (note the 2MiB on 1/100 and 0Mib on 2/100):
Qgroupid Referenced Exclusive Path -------- ---------- --------- ---- 0/5 16.00KiB 16.00KiB <toplevel> 0/256 1.02MiB 1.02MiB sv
Qgroupid Referenced Exclusive Path -------- ---------- --------- ---- 0/5 16.00KiB 16.00KiB <toplevel> 0/256 1.02MiB 1.02MiB sv 1/100 2.03MiB 2.03MiB 2/100<1 member qgroup> 2/100 0.00B 0.00B <0 member qgroups>
With this fix, which simply re-uses `qgroup` as the iteration variable, we see the expected result:
Qgroupid Referenced Exclusive Path -------- ---------- --------- ---- 0/5 16.00KiB 16.00KiB <toplevel> 0/256 1.02MiB 1.02MiB sv
Qgroupid Referenced Exclusive Path -------- ---------- --------- ---- 0/5 16.00KiB 16.00KiB <toplevel> 0/256 1.02MiB 1.02MiB sv 1/100 1.02MiB 1.02MiB 2/100<1 member qgroup> 2/100 1.02MiB 1.02MiB <0 member qgroups>
The existing fstests did not exercise two layer inheritance so this bug was missed. I intend to add that testing there, as well.
Fixes: a0bdc04b0732 ("btrfs: qgroup: use qgroup_iterator in __qgroup_excl_accounting()") CC: stable@vger.kernel.org # 6.12+ Reviewed-by: Filipe Manana fdmanana@suse.com Signed-off-by: Boris Burkov boris@bur.io Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/btrfs/qgroup.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)
--- a/fs/btrfs/qgroup.c +++ b/fs/btrfs/qgroup.c @@ -1481,7 +1481,6 @@ static int __qgroup_excl_accounting(stru struct btrfs_qgroup *src, int sign) { struct btrfs_qgroup *qgroup; - struct btrfs_qgroup *cur; LIST_HEAD(qgroup_list); u64 num_bytes = src->excl; int ret = 0; @@ -1491,7 +1490,7 @@ static int __qgroup_excl_accounting(stru goto out;
qgroup_iterator_add(&qgroup_list, qgroup); - list_for_each_entry(cur, &qgroup_list, iterator) { + list_for_each_entry(qgroup, &qgroup_list, iterator) { struct btrfs_qgroup_list *glist;
qgroup->rfer += sign * num_bytes;