[PATCH 5.4 19/27] btrfs: qgroup: allow to unreserve range without releasing other ranges

Greg Kroah-Hartman
2021-08-13T15:15:10Z

From: Qu Wenruo <wqu@suse.com>

commit 263da812e87bac4098a4778efaa32c54275641db upstream

[PROBLEM]
Before this patch, when btrfs_qgroup_reserve_data() fails, we free all
reserved space of the changeset.

For example:
ret = btrfs_qgroup_reserve_data(inode, changeset, 0, SZ_1M);
ret = btrfs_qgroup_reserve_data(inode, changeset, SZ_1M, SZ_1M);
ret = btrfs_qgroup_reserve_data(inode, changeset, SZ_2M, SZ_1M);

If the last btrfs_qgroup_reserve_data() failed, it will release the
entire [0, 3M) range.

This behavior is kind of OK for now, as when we hit -EDQUOT, we normally
go error handling and need to release all reserved ranges anyway.

But this also means the following call is not possible:

ret = btrfs_qgroup_reserve_data();
if (ret == -EDQUOT) {
/* Do something to free some qgroup space */
ret = btrfs_qgroup_reserve_data();
}

As if the first btrfs_qgroup_reserve_data() fails, it will free all
reserved qgroup space.

[CAUSE]
This is because we release all reserved ranges when
btrfs_qgroup_reserve_data() fails.

[FIX]
This patch will implement a new function, qgroup_unreserve_range(), to
iterate through the ulist nodes, to find any nodes in the failure range,
and remove the EXTENT_QGROUP_RESERVED bits from the io_tree, and
decrease the extent_changeset::bytes_changed, so that we can revert to
previous state.

This allows later patches to retry btrfs_qgroup_reserve_data() if EDQUOT
happens.

Suggested-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/btrfs/qgroup.c | 92 +++++++++++++++++++++++++++++++++++++++++++++---------
1 file changed, 77 insertions(+), 15 deletions(-)

--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -3411,6 +3411,73 @@ btrfs_qgroup_rescan_resume(struct btrfs_
}
}

+#define rbtree_iterate_from_safe(node, next, start) \
+ for (node = start; node && ({ next = rb_next(node); 1;}); node = next)
+
+static int qgroup_unreserve_range(struct btrfs_inode *inode,
+ struct extent_changeset *reserved, u64 start,
+ u64 len)
+{
+ struct rb_node *node;
+ struct rb_node *next;
+ struct ulist_node *entry = NULL;
+ int ret = 0;
+
+ node = reserved->range_changed.root.rb_node;
+ while (node) {
+ entry = rb_entry(node, struct ulist_node, rb_node);
+ if (entry->val < start)
+ node = node->rb_right;
+ else if (entry)
+ node = node->rb_left;
+ else
+ break;
+ }
+
+ /* Empty changeset */
+ if (!entry)
+ return 0;
+
+ if (entry->val > start && rb_prev(&entry->rb_node))
+ entry = rb_entry(rb_prev(&entry->rb_node), struct ulist_node,
+ rb_node);
+
+ rbtree_iterate_from_safe(node, next, &entry->rb_node) {
+ u64 entry_start;
+ u64 entry_end;
+ u64 entry_len;
+ int clear_ret;
+
+ entry = rb_entry(node, struct ulist_node, rb_node);
+ entry_start = entry->val;
+ entry_end = entry->aux;
+ entry_len = entry_end - entry_start + 1;
+
+ if (entry_start >= start + len)
+ break;
+ if (entry_start + entry_len <= start)
+ continue;
+ /*
+ * Now the entry is in [start, start + len), revert the
+ * EXTENT_QGROUP_RESERVED bit.
+ */
+ clear_ret = clear_extent_bits(&inode->io_tree, entry_start,
+ entry_end, EXTENT_QGROUP_RESERVED);
+ if (!ret && clear_ret < 0)
+ ret = clear_ret;
+
+ ulist_del(&reserved->range_changed, entry->val, entry->aux);
+ if (likely(reserved->bytes_changed >= entry_len)) {
+ reserved->bytes_changed -= entry_len;
+ } else {
+ WARN_ON(1);
+ reserved->bytes_changed = 0;
+ }
+ }
+
+ return ret;
+}
+
/*
* Reserve qgroup space for range [start, start + len).
*
@@ -3421,18 +3488,14 @@ btrfs_qgroup_rescan_resume(struct btrfs_
* Return <0 for error (including -EQUOT)
*
* NOTE: this function may sleep for memory allocation.
- * if btrfs_qgroup_reserve_data() is called multiple times with
- * same @reserved, caller must ensure when error happens it's OK
- * to free *ALL* reserved space.
*/
int btrfs_qgroup_reserve_data(struct btrfs_inode *inode,
struct extent_changeset **reserved_ret, u64 start,
u64 len)
{
struct btrfs_root *root = inode->root;
- struct ulist_node *unode;
- struct ulist_iterator uiter;
struct extent_changeset *reserved;
+ bool new_reserved = false;
u64 orig_reserved;
u64 to_reserve;
int ret;
@@ -3445,6 +3508,7 @@ int btrfs_qgroup_reserve_data(struct btr
if (WARN_ON(!reserved_ret))
return -EINVAL;
if (!*reserved_ret) {
+ new_reserved = true;
*reserved_ret = extent_changeset_alloc();
if (!*reserved_ret)
return -ENOMEM;
@@ -3460,7 +3524,7 @@ int btrfs_qgroup_reserve_data(struct btr
trace_btrfs_qgroup_reserve_data(&inode->vfs_inode, start, len,
to_reserve, QGROUP_RESERVE);
if (ret < 0)
- goto cleanup;
+ goto out;
ret = qgroup_reserve(root, to_reserve, true, BTRFS_QGROUP_RSV_DATA);
if (ret < 0)
goto cleanup;
@@ -3468,15 +3532,13 @@ int btrfs_qgroup_reserve_data(struct btr
return ret;

cleanup:
- /* cleanup *ALL* already reserved ranges */
- ULIST_ITER_INIT(&uiter);
- while ((unode = ulist_next(&reserved->range_changed, &uiter)))
- clear_extent_bit(&inode->io_tree, unode->val,
- unode->aux, EXTENT_QGROUP_RESERVED, 0, 0, NULL);
- /* Also free data bytes of already reserved one */
- btrfs_qgroup_free_refroot(root->fs_info, root->root_key.objectid,
- orig_reserved, BTRFS_QGROUP_RSV_DATA);
- extent_changeset_release(reserved);
+ qgroup_unreserve_range(inode, reserved, start, len);
+out:
+ if (new_reserved) {
+ extent_changeset_release(reserved);
+ kfree(reserved);
+ *reserved_ret = NULL;
+ }
return ret;
}