* Re: [PATCH v3] btrfs: fix nonzero lowest level handling in btrfs_search_forward()
2025-06-12 8:32 [PATCH v3] btrfs: fix nonzero lowest level handling in btrfs_search_forward() Sun YangKai
@ 2025-06-12 15:51 ` Sun YangKai
2025-06-18 14:49 ` Filipe Manana
1 sibling, 0 replies; 3+ messages in thread
From: Sun YangKai @ 2025-06-12 15:51 UTC (permalink / raw)
To: linux-btrfs
> Commit 323ac95bce44 ("Btrfs: don't read leaf blocks containing only
> checksums during truncate") changed the condition from `level == 0` to
> `level == path->lowest_level`, while its origional purpose is just to do
> some leaf nodes handling (calling btrfs_item_key_to_cpu()) and skip some
> code that doesn't fit leaf nodes.
>
> After changing the condition, the code path
> 1. also handle the non-leaf nodes when path->lowest_level is nonzero,
> which is wrong. However, it seems that btrfs_search_forward() is never
> called with a nonzero path->lowest_level, which makes this bug not
> found before.
> 2. makes the later if block with the same condition, which is origionally
> used to handle non-leaf node (calling btrfs_node_key_to_cpu()) when
> lowest_level is not zero, dead code.
>
> This changes the behavior when btrfs_search_forward() is called with
> nonzero path->lowest_level. But this never happens in the current code
> base, and the previous behavior is wrong. So the change of behavior will
> not be a problem.
>
> Fix: commit 323ac95bce44 ("Btrfs: don't read leaf blocks containing only
> checksums during truncate") Signed-off-by: Sun YangKai
> <sunk67188@gmail.com>
> ---
> fs/btrfs/ctree.c | 18 +++++-------------
> 1 file changed, 5 insertions(+), 13 deletions(-)
>
> diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
> index a2e7979372cc..56a49d85b2a4 100644
> --- a/fs/btrfs/ctree.c
> +++ b/fs/btrfs/ctree.c
> @@ -4585,16 +4585,13 @@ int btrfs_del_items(struct btrfs_trans_handle
> *trans, struct btrfs_root *root,
>
> /*
> * A helper function to walk down the tree starting at min_key, and looking
> - * for nodes or leaves that are have a minimum transaction id.
> + * for leaves that are have a minimum transaction id.
> * This is used by the btree defrag code, and tree logging
> *
> * This does not cow, but it does stuff the starting key it finds back
> * into min_key, so you can call btrfs_search_slot with cow=1 on the
> * key and get a writable path.
> *
> - * This honors path->lowest_level to prevent descent past a given level
> - * of the tree.
> - *
> * min_trans indicates the oldest transaction that you are interested
> * in walking through. Any nodes or leaves older than min_trans are
> * skipped over (without reading them).
> @@ -4615,6 +4612,7 @@ int btrfs_search_forward(struct btrfs_root *root,
> struct btrfs_key *min_key, int keep_locks = path->keep_locks;
>
> ASSERT(!path->nowait);
> + ASSERT(path->lowest_level == 0);
> path->keep_locks = 1;
> again:
> cur = btrfs_read_lock_root_node(root);
> @@ -4636,8 +4634,8 @@ int btrfs_search_forward(struct btrfs_root *root,
> struct btrfs_key *min_key, goto out;
> }
>
> - /* at the lowest level, we're done, setup the path and exit */
> - if (level == path->lowest_level) {
> + /* at the level 0, we're done, setup the path and exit */
> + if (level == 0) {
> if (slot >= nritems)
> goto find_next_key;
> ret = 0;
> @@ -4678,12 +4676,6 @@ int btrfs_search_forward(struct btrfs_root *root,
> struct btrfs_key *min_key, goto out;
> }
> }
> - if (level == path->lowest_level) {
> - ret = 0;
> - /* Save our key for returning back. */
> - btrfs_node_key_to_cpu(cur, min_key, slot);
> - goto out;
> - }
> cur = btrfs_read_node_slot(cur, slot);
> if (IS_ERR(cur)) {
> ret = PTR_ERR(cur);
> @@ -4699,7 +4691,7 @@ int btrfs_search_forward(struct btrfs_root *root,
> struct btrfs_key *min_key, out:
> path->keep_locks = keep_locks;
> if (ret == 0)
> - btrfs_unlock_up_safe(path, path->lowest_level + 1);
> + btrfs_unlock_up_safe(path, 1);
> return ret;
> }
This patch is suggest by Qu Wenruo.
Should I add a line like
Suggest-by: Qu Wenruo <wqu@suse.com>
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH v3] btrfs: fix nonzero lowest level handling in btrfs_search_forward()
2025-06-12 8:32 [PATCH v3] btrfs: fix nonzero lowest level handling in btrfs_search_forward() Sun YangKai
2025-06-12 15:51 ` Sun YangKai
@ 2025-06-18 14:49 ` Filipe Manana
1 sibling, 0 replies; 3+ messages in thread
From: Filipe Manana @ 2025-06-18 14:49 UTC (permalink / raw)
To: Sun YangKai; +Cc: linux-btrfs
On Thu, Jun 12, 2025 at 9:35 AM Sun YangKai <sunk67188@gmail.com> wrote:
>
> Commit 323ac95bce44 ("Btrfs: don't read leaf blocks containing only
> checksums during truncate") changed the condition from `level == 0` to
> `level == path->lowest_level`, while its origional purpose is just to do
origional -> original
> some leaf nodes handling (calling btrfs_item_key_to_cpu()) and skip some
> code that doesn't fit leaf nodes.
>
> After changing the condition, the code path
Add a full colon at the end, so "... the code path:"
Plus a blank line for better readability.
> 1. also handle the non-leaf nodes when path->lowest_level is nonzero,
also -> Also, it's the start of a sentence.
> which is wrong. However, it seems that btrfs_search_forward() is never
Don't say that "it seems" - that gives the idea you are not sure and
haven't checked it.
It's true that it's never called with a path->lowest_level > 0.
> called with a nonzero path->lowest_level, which makes this bug not
> found before.
Another blank line here improves readability.
> 2. makes the later if block with the same condition, which is origionally
makes -> Makes
origionally -> originally
> used to handle non-leaf node (calling btrfs_node_key_to_cpu()) when
> lowest_level is not zero, dead code.
>
> This changes the behavior when btrfs_search_forward() is called with
> nonzero path->lowest_level. But this never happens in the current code
> base, and the previous behavior is wrong. So the change of behavior will
> not be a problem.
Just say something more straightforward and clear such as:
"Since btrfs_search_forward() is nevel called for a path with a
lowest_level different from zero,
just completely remove the partial support for a non-zero
lowest_level, simplifying a bit the code,
and assert that lowest_level is zero at the start of the function."
>
> Fix: commit 323ac95bce44 ("Btrfs: don't read leaf blocks containing only checksums during truncate")
The correct format is:
Fixes: 323ac95bce44 ("Btrfs: don't read leaf blocks containing only
checksums during truncate")
> Signed-off-by: Sun YangKai <sunk67188@gmail.com>
> ---
> fs/btrfs/ctree.c | 18 +++++-------------
> 1 file changed, 5 insertions(+), 13 deletions(-)
>
> diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
> index a2e7979372cc..56a49d85b2a4 100644
> --- a/fs/btrfs/ctree.c
> +++ b/fs/btrfs/ctree.c
> @@ -4585,16 +4585,13 @@ int btrfs_del_items(struct btrfs_trans_handle *trans, struct btrfs_root *root,
>
> /*
> * A helper function to walk down the tree starting at min_key, and looking
> - * for nodes or leaves that are have a minimum transaction id.
> + * for leaves that are have a minimum transaction id.
Since we are updating the comment, it's a good opportunity to fix the grammar.
Replace "that are have a minimum..." with just "that have a minimum...".
> * This is used by the btree defrag code, and tree logging
> *
> * This does not cow, but it does stuff the starting key it finds back
> * into min_key, so you can call btrfs_search_slot with cow=1 on the
> * key and get a writable path.
> *
> - * This honors path->lowest_level to prevent descent past a given level
> - * of the tree.
> - *
> * min_trans indicates the oldest transaction that you are interested
> * in walking through. Any nodes or leaves older than min_trans are
> * skipped over (without reading them).
> @@ -4615,6 +4612,7 @@ int btrfs_search_forward(struct btrfs_root *root, struct btrfs_key *min_key,
> int keep_locks = path->keep_locks;
>
> ASSERT(!path->nowait);
> + ASSERT(path->lowest_level == 0);
> path->keep_locks = 1;
> again:
> cur = btrfs_read_lock_root_node(root);
> @@ -4636,8 +4634,8 @@ int btrfs_search_forward(struct btrfs_root *root, struct btrfs_key *min_key,
> goto out;
> }
>
> - /* at the lowest level, we're done, setup the path and exit */
> - if (level == path->lowest_level) {
> + /* at the level 0, we're done, setup the path and exit */
Since the comment is being modified, it's a good opportunity to fix
the style for what we prefer nowadays: capitalize the first word and
add ending punctuation.
Finally, answering your question from the reply you made later:
Yes, "Suggested-by: Qu Wenruo <wqu@suse.com>" can be added, but
there's no need to resend a patch just for that.
Also note that the tag is Suggested-by, and not Suggest-by as you typed.
If you agree, I can update the patch with all those changes and add it
to for-next, let me know.
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Thanks.
> + if (level == 0) {
> if (slot >= nritems)
> goto find_next_key;
> ret = 0;
> @@ -4678,12 +4676,6 @@ int btrfs_search_forward(struct btrfs_root *root, struct btrfs_key *min_key,
> goto out;
> }
> }
> - if (level == path->lowest_level) {
> - ret = 0;
> - /* Save our key for returning back. */
> - btrfs_node_key_to_cpu(cur, min_key, slot);
> - goto out;
> - }
> cur = btrfs_read_node_slot(cur, slot);
> if (IS_ERR(cur)) {
> ret = PTR_ERR(cur);
> @@ -4699,7 +4691,7 @@ int btrfs_search_forward(struct btrfs_root *root, struct btrfs_key *min_key,
> out:
> path->keep_locks = keep_locks;
> if (ret == 0)
> - btrfs_unlock_up_safe(path, path->lowest_level + 1);
> + btrfs_unlock_up_safe(path, 1);
> return ret;
> }
>
> --
> 2.49.0
>
>
^ permalink raw reply [flat|nested] 3+ messages in thread