[PATCH 3/3] btrfs: allow device add if balance is paused

Nikolay Borisov
2021-11-01T11:53:31Z

Currently paused balance precludes adding a device since they are both
considered exclusive ops and we can have at most 1 running at a time.
This is problematic in case a filesystem encounters an ENOSPC situation
while balance is running, in this case the only thing the user can do
is mount the fs with "skip_balance" which pauses balance and delete some
data to free up space for balance. However, it should be possible to add
a new device when balance is paused.

Fix this by allowing device add to proceed when balance is paused.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
---
fs/btrfs/ioctl.c | 24 +++++++++++++++++++++---
1 file changed, 21 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 05969e2f4536..8e34dceee96b 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3149,13 +3149,25 @@ static int btrfs_ioctl_defrag(struct file *file, void __user *argp)
static long btrfs_ioctl_add_dev(struct btrfs_fs_info *fs_info, void __user *arg)
{
struct btrfs_ioctl_vol_args *vol_args;
+ bool restore_op = false;
int ret;

if (!capable(CAP_SYS_ADMIN))
return -EPERM;

- if (!btrfs_exclop_start(fs_info, BTRFS_EXCLOP_DEV_ADD))
- return BTRFS_ERROR_DEV_EXCL_RUN_IN_PROGRESS;
+ if (!btrfs_exclop_start(fs_info, BTRFS_EXCLOP_DEV_ADD)) {
+ if (!btrfs_exclop_start_try_lock(fs_info, BTRFS_EXCLOP_DEV_ADD))
+ return BTRFS_ERROR_DEV_EXCL_RUN_IN_PROGRESS;
+
+ /*
+ * We can do the device add because we have a paused balanced,
+ * change the exclusive op type and remember we should bring
+ * back the paused balance
+ */
+ fs_info->exclusive_operation = BTRFS_EXCLOP_DEV_ADD;
+ btrfs_exclop_start_unlock(fs_info);
+ restore_op = true;
+ }

vol_args = memdup_user(arg, sizeof(*vol_args));
if (IS_ERR(vol_args)) {
@@ -3171,7 +3183,13 @@ static long btrfs_ioctl_add_dev(struct btrfs_fs_info *fs_info, void __user *arg)

kfree(vol_args);
out:
- btrfs_exclop_finish(fs_info);
+ if (restore_op) {
+ spin_lock(&fs_info->super_lock);
+ fs_info->exclusive_operation = BTRFS_EXCLOP_BALANCE_PAUSED;
+ spin_unlock(&fs_info->super_lock);
+ } else {
+ btrfs_exclop_finish(fs_info);
+ }
return ret;
}

--
2.25.1