[PATCH v2 1/2] btrfs: Add support to do stack item key operation

[PATCH v2 1/2] btrfs: Add support to do stack item key operation

[Qu Wenruo]

Normal btrfs_item_key_to_cpu() will need extent buffer to do it, and
there is not stack version to handle in memory leaf.

Add btrfs_stack_item_key_to_cpu() function for such operation, which
will provide the basis for later qgroup fix.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
---
v2:
  Change the char* parameter to struct btrfs_header *, as a leaf always
  starts with a header.
---
 fs/btrfs/ctree.h | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 938efe3..4864dfe 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -2683,6 +2683,17 @@ static inline void btrfs_item_key(struct extent_buffer *eb,
 	read_eb_member(eb, item, struct btrfs_item, key, disk_key);
 }
 
+static inline void btrfs_stack_item_key(struct btrfs_header *stack_leaf,
+					struct btrfs_disk_key *disk_key,
+					int nr)
+{
+	unsigned long item_offset = btrfs_item_nr_offset(nr);
+	struct btrfs_item *item;
+
+	item = (struct btrfs_item *)(stack_leaf + item_offset);
+	memcpy(disk_key, &item->key, sizeof(*disk_key));
+}
+
 static inline void btrfs_set_item_key(struct extent_buffer *eb,
 			       struct btrfs_disk_key *disk_key, int nr)
 {
@@ -2785,6 +2796,15 @@ static inline void btrfs_item_key_to_cpu(struct extent_buffer *eb,
 	btrfs_disk_key_to_cpu(key, &disk_key);
 }
 
+static inline void btrfs_stack_item_key_to_cpu(struct btrfs_header *stack_leaf,
+					       struct btrfs_key *key,
+					       int nr)
+{
+	struct btrfs_disk_key disk_key;
+	btrfs_stack_item_key(stack_leaf, &disk_key, nr);
+	btrfs_disk_key_to_cpu(key, &disk_key);
+}
+
 static inline void btrfs_dir_item_key_to_cpu(struct extent_buffer *eb,
 				      struct btrfs_dir_item *item,
 				      struct btrfs_key *key)
-- 
2.5.3

[PATCH v2 2/2] btrfs: qgroup: Don't copy extent buffer to do qgroup rescan

[Qu Wenruo]

Ancient qgroup code call memcpy() on a extent buffer and use it for leaf
iteration.

As extent buffer contains lock, pointers to pages, it's never sane to do
such copy.

The following bug may be caused by this insane operation:
[92098.841309] general protection fault: 0000 [#1] SMP
[92098.841338] Modules linked in: ...
[92098.841814] CPU: 1 PID: 24655 Comm: kworker/u4:12 Not tainted
4.3.0-rc1 #1
[92098.841868] Workqueue: btrfs-qgroup-rescan btrfs_qgroup_rescan_helper
[btrfs]
[92098.842261] Call Trace:
[92098.842277]  [<ffffffffc035a5d8>] ? read_extent_buffer+0xb8/0x110
[btrfs]
[92098.842304]  [<ffffffffc0396d00>] ? btrfs_find_all_roots+0x60/0x70
[btrfs]
[92098.842329]  [<ffffffffc039af3d>]
btrfs_qgroup_rescan_worker+0x28d/0x5a0 [btrfs]

Where btrfs_qgroup_rescan_worker+0x28d is btrfs_disk_key_to_cpu(),
called in reading key from the memcpied extent_buffer.

This patch will read the whole leaf into memory, and use newly
introduced stack function to do qgroup rescan.

Reported-by: Stephane Lesimple <stephane_btrfs@lesimple.fr>
Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
---
v2:
  Follow the parameter change in previous patch.
---
 fs/btrfs/qgroup.c | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index e9ace09..6a83a40 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -2183,11 +2183,11 @@ void assert_qgroups_uptodate(struct btrfs_trans_handle *trans)
  */
 static int
 qgroup_rescan_leaf(struct btrfs_fs_info *fs_info, struct btrfs_path *path,
-		   struct btrfs_trans_handle *trans,
-		   struct extent_buffer *scratch_leaf)
+		   struct btrfs_trans_handle *trans, char *stack_leaf)
 {
 	struct btrfs_key found;
 	struct ulist *roots = NULL;
+	struct btrfs_header *header;
 	struct seq_list tree_mod_seq_elem = SEQ_LIST_INIT(tree_mod_seq_elem);
 	u64 num_bytes;
 	int slot;
@@ -2224,13 +2224,15 @@ qgroup_rescan_leaf(struct btrfs_fs_info *fs_info, struct btrfs_path *path,
 	fs_info->qgroup_rescan_progress.objectid = found.objectid + 1;
 
 	btrfs_get_tree_mod_seq(fs_info, &tree_mod_seq_elem);
-	memcpy(scratch_leaf, path->nodes[0], sizeof(*scratch_leaf));
+	read_extent_buffer(path->nodes[0], stack_leaf, 0,
+			   fs_info->extent_root->nodesize);
+	header = (struct btrfs_header *)stack_leaf;
 	slot = path->slots[0];
 	btrfs_release_path(path);
 	mutex_unlock(&fs_info->qgroup_rescan_lock);
 
-	for (; slot < btrfs_header_nritems(scratch_leaf); ++slot) {
-		btrfs_item_key_to_cpu(scratch_leaf, &found, slot);
+	for (; slot < btrfs_stack_header_nritems(header); ++slot) {
+		btrfs_stack_item_key_to_cpu(header, &found, slot);
 		if (found.type != BTRFS_EXTENT_ITEM_KEY &&
 		    found.type != BTRFS_METADATA_ITEM_KEY)
 			continue;
@@ -2261,15 +2263,15 @@ static void btrfs_qgroup_rescan_worker(struct btrfs_work *work)
 						     qgroup_rescan_work);
 	struct btrfs_path *path;
 	struct btrfs_trans_handle *trans = NULL;
-	struct extent_buffer *scratch_leaf = NULL;
+	char *stack_leaf = NULL;
 	int err = -ENOMEM;
 	int ret = 0;
 
 	path = btrfs_alloc_path();
 	if (!path)
 		goto out;
-	scratch_leaf = kmalloc(sizeof(*scratch_leaf), GFP_NOFS);
-	if (!scratch_leaf)
+	stack_leaf = kmalloc(fs_info->extent_root->nodesize, GFP_NOFS);
+	if (!stack_leaf)
 		goto out;
 
 	err = 0;
@@ -2283,7 +2285,7 @@ static void btrfs_qgroup_rescan_worker(struct btrfs_work *work)
 			err = -EINTR;
 		} else {
 			err = qgroup_rescan_leaf(fs_info, path, trans,
-						 scratch_leaf);
+						 stack_leaf);
 		}
 		if (err > 0)
 			btrfs_commit_transaction(trans, fs_info->fs_root);
@@ -2292,7 +2294,7 @@ static void btrfs_qgroup_rescan_worker(struct btrfs_work *work)
 	}
 
 out:
-	kfree(scratch_leaf);
+	kfree(stack_leaf);
 	btrfs_free_path(path);
 
 	mutex_lock(&fs_info->qgroup_rescan_lock);
-- 
2.5.3

Re: [PATCH v2 1/2] btrfs: Add support to do stack item key operation

[Qu Wenruo]

Qu Wenruo wrote on 2015/10/06 08:58 +0800:
> Normal btrfs_item_key_to_cpu() will need extent buffer to do it, and
> there is not stack version to handle in memory leaf.
>
> Add btrfs_stack_item_key_to_cpu() function for such operation, which
> will provide the basis for later qgroup fix.
>
> Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
> ---
> v2:
>    Change the char* parameter to struct btrfs_header *, as a leaf always
>    starts with a header.
> ---
>   fs/btrfs/ctree.h | 20 ++++++++++++++++++++
>   1 file changed, 20 insertions(+)
>
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index 938efe3..4864dfe 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -2683,6 +2683,17 @@ static inline void btrfs_item_key(struct extent_buffer *eb,
>   	read_eb_member(eb, item, struct btrfs_item, key, disk_key);
>   }
>
> +static inline void btrfs_stack_item_key(struct btrfs_header *stack_leaf,
> +					struct btrfs_disk_key *disk_key,
> +					int nr)
> +{
> +	unsigned long item_offset = btrfs_item_nr_offset(nr);
> +	struct btrfs_item *item;
> +
> +	item = (struct btrfs_item *)(stack_leaf + item_offset);
Please ignore this version, as I changed the type of stack_leaf but 
didn't force convert it to (char *).

I'll update it soon.

Thanks,
Qu
> +	memcpy(disk_key, &item->key, sizeof(*disk_key));
> +}
> +
>   static inline void btrfs_set_item_key(struct extent_buffer *eb,
>   			       struct btrfs_disk_key *disk_key, int nr)
>   {
> @@ -2785,6 +2796,15 @@ static inline void btrfs_item_key_to_cpu(struct extent_buffer *eb,
>   	btrfs_disk_key_to_cpu(key, &disk_key);
>   }
>
> +static inline void btrfs_stack_item_key_to_cpu(struct btrfs_header *stack_leaf,
> +					       struct btrfs_key *key,
> +					       int nr)
> +{
> +	struct btrfs_disk_key disk_key;
> +	btrfs_stack_item_key(stack_leaf, &disk_key, nr);
> +	btrfs_disk_key_to_cpu(key, &disk_key);
> +}
> +
>   static inline void btrfs_dir_item_key_to_cpu(struct extent_buffer *eb,
>   				      struct btrfs_dir_item *item,
>   				      struct btrfs_key *key)
>