struct btrfs_path *p,
int write_lock_level)
{
- struct btrfs_fs_info *fs_info = root->fs_info;
struct extent_buffer *b;
int root_lock = 0;
int level = 0;
if (p->search_commit_root) {
- /*
- * The commit roots are read only so we always do read locks,
- * and we always must hold the commit_root_sem when doing
- * searches on them, the only exception is send where we don't
- * want to block transaction commits for a long time, so
- * we need to clone the commit root in order to avoid races
- * with transaction commits that create a snapshot of one of
- * the roots used by a send operation.
- */
- if (p->need_commit_sem) {
- down_read(&fs_info->commit_root_sem);
- b = btrfs_clone_extent_buffer(root->commit_root);
- up_read(&fs_info->commit_root_sem);
- if (!b)
- return ERR_PTR(-ENOMEM);
-
- } else {
- b = root->commit_root;
- atomic_inc(&b->refs);
- }
+ b = root->commit_root;
+ atomic_inc(&b->refs);
level = btrfs_header_level(b);
/*
* Ensure that all callers have set skip_locking when
return b;
}
+/*
+ * Replace the extent buffer at the lowest level of the path with a cloned
+ * version. The purpose is to be able to use it safely, after releasing the
+ * commit root semaphore, even if relocation is happening in parallel, the
+ * transaction used for relocation is committed and the extent buffer is
+ * reallocated in the next transaction.
+ *
+ * This is used in a context where the caller does not prevent transaction
+ * commits from happening, either by holding a transaction handle or holding
+ * some lock, while it's doing searches through a commit root.
+ * At the moment it's only used for send operations.
+ */
+static int finish_need_commit_sem_search(struct btrfs_path *path)
+{
+ const int i = path->lowest_level;
+ const int slot = path->slots[i];
+ struct extent_buffer *lowest = path->nodes[i];
+ struct extent_buffer *clone;
+
+ ASSERT(path->need_commit_sem);
+
+ if (!lowest)
+ return 0;
+
+ lockdep_assert_held_read(&lowest->fs_info->commit_root_sem);
+
+ clone = btrfs_clone_extent_buffer(lowest);
+ if (!clone)
+ return -ENOMEM;
+
+ btrfs_release_path(path);
+ path->nodes[i] = clone;
+ path->slots[i] = slot;
+
+ return 0;
+}
/*
* btrfs_search_slot - look for a key in a tree and perform necessary
const struct btrfs_key *key, struct btrfs_path *p,
int ins_len, int cow)
{
+ struct btrfs_fs_info *fs_info = root->fs_info;
struct extent_buffer *b;
int slot;
int ret;
min_write_lock_level = write_lock_level;
+ if (p->need_commit_sem) {
+ ASSERT(p->search_commit_root);
+ down_read(&fs_info->commit_root_sem);
+ }
+
again:
prev_cmp = -1;
b = btrfs_search_slot_get_root(root, p, write_lock_level);
done:
if (ret < 0 && !p->skip_release_on_error)
btrfs_release_path(p);
+
+ if (p->need_commit_sem) {
+ int ret2;
+
+ ret2 = finish_need_commit_sem_search(p);
+ up_read(&fs_info->commit_root_sem);
+ if (ret2)
+ ret = ret2;
+ }
+
return ret;
}
ALLOW_ERROR_INJECTION(btrfs_search_slot, ERRNO);
int level;
struct extent_buffer *c;
struct extent_buffer *next;
+ struct btrfs_fs_info *fs_info = root->fs_info;
struct btrfs_key key;
+ bool need_commit_sem = false;
u32 nritems;
int ret;
int i;
path->keep_locks = 1;
- if (time_seq)
+ if (time_seq) {
ret = btrfs_search_old_slot(root, &key, path, time_seq);
- else
+ } else {
+ if (path->need_commit_sem) {
+ path->need_commit_sem = 0;
+ need_commit_sem = true;
+ down_read(&fs_info->commit_root_sem);
+ }
ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
+ }
path->keep_locks = 0;
if (ret < 0)
- return ret;
+ goto done;
nritems = btrfs_header_nritems(path->nodes[0]);
/*
ret = 0;
done:
unlock_up(path, 0, 1, 0, NULL);
+ if (need_commit_sem) {
+ int ret2;
+
+ path->need_commit_sem = 1;
+ ret2 = finish_need_commit_sem_search(path);
+ up_read(&fs_info->commit_root_sem);
+ if (ret2)
+ ret = ret2;
+ }
return ret;
}
#include "transaction.h"
#include "compression.h"
#include "xattr.h"
+#include "print-tree.h"
/*
* Maximum number of references an extent can have in order for us to attempt to
struct btrfs_path *right_path;
struct btrfs_key *cmp_key;
+ /*
+ * Keep track of the generation of the last transaction that was used
+ * for relocating a block group. This is periodically checked in order
+ * to detect if a relocation happened since the last check, so that we
+ * don't operate on stale extent buffers for nodes (level >= 1) or on
+ * stale disk_bytenr values of file extent items.
+ */
+ u64 last_reloc_trans;
+
/*
* infos of the currently processed inode. In case of deleted inodes,
* these are the values from the deleted inode.
if (ret < 0)
goto out;
+ down_read(&fs_info->commit_root_sem);
+ if (fs_info->last_reloc_trans > sctx->last_reloc_trans) {
+ /*
+ * A transaction commit for a transaction in which block group
+ * relocation was done just happened.
+ * The disk_bytenr of the file extent item we processed is
+ * possibly stale, referring to the extent's location before
+ * relocation. So act as if we haven't found any clone sources
+ * and fallback to write commands, which will read the correct
+ * data from the new extent location. Otherwise we will fail
+ * below because we haven't found our own back reference or we
+ * could be getting incorrect sources in case the old extent
+ * was already reallocated after the relocation.
+ */
+ up_read(&fs_info->commit_root_sem);
+ ret = -ENOENT;
+ goto out;
+ }
+ up_read(&fs_info->commit_root_sem);
+
if (!backref_ctx.found_itself) {
/* found a bug in backref code? */
ret = -EIO;
{
int ret = 0;
+ /*
+ * We can not hold the commit root semaphore here. This is because in
+ * the case of sending and receiving to the same filesystem, using a
+ * pipe, could result in a deadlock:
+ *
+ * 1) The task running send blocks on the pipe because it's full;
+ *
+ * 2) The task running receive, which is the only consumer of the pipe,
+ * is waiting for a transaction commit (for example due to a space
+ * reservation when doing a write or triggering a transaction commit
+ * when creating a subvolume);
+ *
+ * 3) The transaction is waiting to write lock the commit root semaphore,
+ * but can not acquire it since it's being held at 1).
+ *
+ * Down this call chain we write to the pipe through kernel_write().
+ * The same type of problem can also happen when sending to a file that
+ * is stored in the same filesystem - when reserving space for a write
+ * into the file, we can trigger a transaction commit.
+ *
+ * Our caller has supplied us with clones of leaves from the send and
+ * parent roots, so we're safe here from a concurrent relocation and
+ * further reallocation of metadata extents while we are here. Below we
+ * also assert that the leaves are clones.
+ */
+ lockdep_assert_not_held(&sctx->send_root->fs_info->commit_root_sem);
+
+ /*
+ * We always have a send root, so left_path is never NULL. We will not
+ * have a leaf when we have reached the end of the send root but have
+ * not yet reached the end of the parent root.
+ */
+ if (left_path->nodes[0])
+ ASSERT(test_bit(EXTENT_BUFFER_UNMAPPED,
+ &left_path->nodes[0]->bflags));
+ /*
+ * When doing a full send we don't have a parent root, so right_path is
+ * NULL. When doing an incremental send, we may have reached the end of
+ * the parent root already, so we don't have a leaf at right_path.
+ */
+ if (right_path && right_path->nodes[0])
+ ASSERT(test_bit(EXTENT_BUFFER_UNMAPPED,
+ &right_path->nodes[0]->bflags));
+
if (result == BTRFS_COMPARE_TREE_SAME) {
if (key->type == BTRFS_INODE_REF_KEY ||
key->type == BTRFS_INODE_EXTREF_KEY) {
return ret;
}
+static int search_key_again(const struct send_ctx *sctx,
+ struct btrfs_root *root,
+ struct btrfs_path *path,
+ const struct btrfs_key *key)
+{
+ int ret;
+
+ if (!path->need_commit_sem)
+ lockdep_assert_held_read(&root->fs_info->commit_root_sem);
+
+ /*
+ * Roots used for send operations are readonly and no one can add,
+ * update or remove keys from them, so we should be able to find our
+ * key again. The only exception is deduplication, which can operate on
+ * readonly roots and add, update or remove keys to/from them - but at
+ * the moment we don't allow it to run in parallel with send.
+ */
+ ret = btrfs_search_slot(NULL, root, key, path, 0, 0);
+ ASSERT(ret <= 0);
+ if (ret > 0) {
+ btrfs_print_tree(path->nodes[path->lowest_level], false);
+ btrfs_err(root->fs_info,
+"send: key (%llu %u %llu) not found in %s root %llu, lowest_level %d, slot %d",
+ key->objectid, key->type, key->offset,
+ (root == sctx->parent_root ? "parent" : "send"),
+ root->root_key.objectid, path->lowest_level,
+ path->slots[path->lowest_level]);
+ return -EUCLEAN;
+ }
+
+ return ret;
+}
+
static int full_send_tree(struct send_ctx *sctx)
{
int ret;
struct btrfs_root *send_root = sctx->send_root;
struct btrfs_key key;
+ struct btrfs_fs_info *fs_info = send_root->fs_info;
struct btrfs_path *path;
- struct extent_buffer *eb;
- int slot;
path = alloc_path_for_send();
if (!path)
key.type = BTRFS_INODE_ITEM_KEY;
key.offset = 0;
+ down_read(&fs_info->commit_root_sem);
+ sctx->last_reloc_trans = fs_info->last_reloc_trans;
+ up_read(&fs_info->commit_root_sem);
+
ret = btrfs_search_slot_for_read(send_root, &key, path, 1, 0);
if (ret < 0)
goto out;
goto out_finish;
while (1) {
- eb = path->nodes[0];
- slot = path->slots[0];
- btrfs_item_key_to_cpu(eb, &key, slot);
+ btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
ret = changed_cb(path, NULL, &key,
BTRFS_COMPARE_TREE_NEW, sctx);
if (ret < 0)
goto out;
+ down_read(&fs_info->commit_root_sem);
+ if (fs_info->last_reloc_trans > sctx->last_reloc_trans) {
+ sctx->last_reloc_trans = fs_info->last_reloc_trans;
+ up_read(&fs_info->commit_root_sem);
+ /*
+ * A transaction used for relocating a block group was
+ * committed or is about to finish its commit. Release
+ * our path (leaf) and restart the search, so that we
+ * avoid operating on any file extent items that are
+ * stale, with a disk_bytenr that reflects a pre
+ * relocation value. This way we avoid as much as
+ * possible to fallback to regular writes when checking
+ * if we can clone file ranges.
+ */
+ btrfs_release_path(path);
+ ret = search_key_again(sctx, send_root, path, &key);
+ if (ret < 0)
+ goto out;
+ } else {
+ up_read(&fs_info->commit_root_sem);
+ }
+
ret = btrfs_next_item(send_root, path);
if (ret < 0)
goto out;
return ret;
}
+static int replace_node_with_clone(struct btrfs_path *path, int level)
+{
+ struct extent_buffer *clone;
+
+ clone = btrfs_clone_extent_buffer(path->nodes[level]);
+ if (!clone)
+ return -ENOMEM;
+
+ free_extent_buffer(path->nodes[level]);
+ path->nodes[level] = clone;
+
+ return 0;
+}
+
static int tree_move_down(struct btrfs_path *path, int *level, u64 reada_min_gen)
{
struct extent_buffer *eb;
u64 reada_max;
u64 reada_done = 0;
+ lockdep_assert_held_read(&parent->fs_info->commit_root_sem);
+
BUG_ON(*level == 0);
eb = btrfs_read_node_slot(parent, slot);
if (IS_ERR(eb))
path->nodes[*level - 1] = eb;
path->slots[*level - 1] = 0;
(*level)--;
+
+ if (*level == 0)
+ return replace_node_with_clone(path, 0);
+
return 0;
}
path->slots[*level]++;
while (path->slots[*level] >= nritems) {
- if (*level == root_level)
+ if (*level == root_level) {
+ path->slots[*level] = nritems - 1;
return -1;
+ }
/* move upnext */
path->slots[*level] = 0;
} else {
ret = tree_move_down(path, level, reada_min_gen);
}
- if (ret >= 0) {
- if (*level == 0)
- btrfs_item_key_to_cpu(path->nodes[*level], key,
- path->slots[*level]);
- else
- btrfs_node_key_to_cpu(path->nodes[*level], key,
- path->slots[*level]);
- }
+
+ /*
+ * Even if we have reached the end of a tree, ret is -1, update the key
+ * anyway, so that in case we need to restart due to a block group
+ * relocation, we can assert that the last key of the root node still
+ * exists in the tree.
+ */
+ if (*level == 0)
+ btrfs_item_key_to_cpu(path->nodes[*level], key,
+ path->slots[*level]);
+ else
+ btrfs_node_key_to_cpu(path->nodes[*level], key,
+ path->slots[*level]);
+
return ret;
}
return 0;
}
+/*
+ * A transaction used for relocating a block group was committed or is about to
+ * finish its commit. Release our paths and restart the search, so that we are
+ * not using stale extent buffers:
+ *
+ * 1) For levels > 0, we are only holding references of extent buffers, without
+ * any locks on them, which does not prevent them from having been relocated
+ * and reallocated after the last time we released the commit root semaphore.
+ * The exception are the root nodes, for which we always have a clone, see
+ * the comment at btrfs_compare_trees();
+ *
+ * 2) For leaves, level 0, we are holding copies (clones) of extent buffers, so
+ * we are safe from the concurrent relocation and reallocation. However they
+ * can have file extent items with a pre relocation disk_bytenr value, so we
+ * restart the start from the current commit roots and clone the new leaves so
+ * that we get the post relocation disk_bytenr values. Not doing so, could
+ * make us clone the wrong data in case there are new extents using the old
+ * disk_bytenr that happen to be shared.
+ */
+static int restart_after_relocation(struct btrfs_path *left_path,
+ struct btrfs_path *right_path,
+ const struct btrfs_key *left_key,
+ const struct btrfs_key *right_key,
+ int left_level,
+ int right_level,
+ const struct send_ctx *sctx)
+{
+ int root_level;
+ int ret;
+
+ lockdep_assert_held_read(&sctx->send_root->fs_info->commit_root_sem);
+
+ btrfs_release_path(left_path);
+ btrfs_release_path(right_path);
+
+ /*
+ * Since keys can not be added or removed to/from our roots because they
+ * are readonly and we do not allow deduplication to run in parallel
+ * (which can add, remove or change keys), the layout of the trees should
+ * not change.
+ */
+ left_path->lowest_level = left_level;
+ ret = search_key_again(sctx, sctx->send_root, left_path, left_key);
+ if (ret < 0)
+ return ret;
+
+ right_path->lowest_level = right_level;
+ ret = search_key_again(sctx, sctx->parent_root, right_path, right_key);
+ if (ret < 0)
+ return ret;
+
+ /*
+ * If the lowest level nodes are leaves, clone them so that they can be
+ * safely used by changed_cb() while not under the protection of the
+ * commit root semaphore, even if relocation and reallocation happens in
+ * parallel.
+ */
+ if (left_level == 0) {
+ ret = replace_node_with_clone(left_path, 0);
+ if (ret < 0)
+ return ret;
+ }
+
+ if (right_level == 0) {
+ ret = replace_node_with_clone(right_path, 0);
+ if (ret < 0)
+ return ret;
+ }
+
+ /*
+ * Now clone the root nodes (unless they happen to be the leaves we have
+ * already cloned). This is to protect against concurrent snapshotting of
+ * the send and parent roots (see the comment at btrfs_compare_trees()).
+ */
+ root_level = btrfs_header_level(sctx->send_root->commit_root);
+ if (root_level > 0) {
+ ret = replace_node_with_clone(left_path, root_level);
+ if (ret < 0)
+ return ret;
+ }
+
+ root_level = btrfs_header_level(sctx->parent_root->commit_root);
+ if (root_level > 0) {
+ ret = replace_node_with_clone(right_path, root_level);
+ if (ret < 0)
+ return ret;
+ }
+
+ return 0;
+}
+
/*
* This function compares two trees and calls the provided callback for
* every changed/new/deleted item it finds.
int right_root_level;
int left_level;
int right_level;
- int left_end_reached;
- int right_end_reached;
- int advance_left;
- int advance_right;
+ int left_end_reached = 0;
+ int right_end_reached = 0;
+ int advance_left = 0;
+ int advance_right = 0;
u64 left_blockptr;
u64 right_blockptr;
u64 left_gen;
down_read(&fs_info->commit_root_sem);
left_level = btrfs_header_level(left_root->commit_root);
left_root_level = left_level;
+ /*
+ * We clone the root node of the send and parent roots to prevent races
+ * with snapshot creation of these roots. Snapshot creation COWs the
+ * root node of a tree, so after the transaction is committed the old
+ * extent can be reallocated while this send operation is still ongoing.
+ * So we clone them, under the commit root semaphore, to be race free.
+ */
left_path->nodes[left_level] =
btrfs_clone_extent_buffer(left_root->commit_root);
if (!left_path->nodes[left_level]) {
- up_read(&fs_info->commit_root_sem);
ret = -ENOMEM;
- goto out;
+ goto out_unlock;
}
right_level = btrfs_header_level(right_root->commit_root);
right_path->nodes[right_level] =
btrfs_clone_extent_buffer(right_root->commit_root);
if (!right_path->nodes[right_level]) {
- up_read(&fs_info->commit_root_sem);
ret = -ENOMEM;
- goto out;
+ goto out_unlock;
}
/*
* Our right root is the parent root, while the left root is the "send"
* will need to read them at some point.
*/
reada_min_gen = btrfs_header_generation(right_root->commit_root);
- up_read(&fs_info->commit_root_sem);
if (left_level == 0)
btrfs_item_key_to_cpu(left_path->nodes[left_level],
btrfs_node_key_to_cpu(right_path->nodes[right_level],
&right_key, right_path->slots[right_level]);
- left_end_reached = right_end_reached = 0;
- advance_left = advance_right = 0;
+ sctx->last_reloc_trans = fs_info->last_reloc_trans;
while (1) {
- cond_resched();
+ if (need_resched() ||
+ rwsem_is_contended(&fs_info->commit_root_sem)) {
+ up_read(&fs_info->commit_root_sem);
+ cond_resched();
+ down_read(&fs_info->commit_root_sem);
+ }
+
+ if (fs_info->last_reloc_trans > sctx->last_reloc_trans) {
+ ret = restart_after_relocation(left_path, right_path,
+ &left_key, &right_key,
+ left_level, right_level,
+ sctx);
+ if (ret < 0)
+ goto out_unlock;
+ sctx->last_reloc_trans = fs_info->last_reloc_trans;
+ }
+
if (advance_left && !left_end_reached) {
ret = tree_advance(left_path, &left_level,
left_root_level,
if (ret == -1)
left_end_reached = ADVANCE;
else if (ret < 0)
- goto out;
+ goto out_unlock;
advance_left = 0;
}
if (advance_right && !right_end_reached) {
if (ret == -1)
right_end_reached = ADVANCE;
else if (ret < 0)
- goto out;
+ goto out_unlock;
advance_right = 0;
}
if (left_end_reached && right_end_reached) {
ret = 0;
- goto out;
+ goto out_unlock;
} else if (left_end_reached) {
if (right_level == 0) {
+ up_read(&fs_info->commit_root_sem);
ret = changed_cb(left_path, right_path,
&right_key,
BTRFS_COMPARE_TREE_DELETED,
sctx);
if (ret < 0)
goto out;
+ down_read(&fs_info->commit_root_sem);
}
advance_right = ADVANCE;
continue;
} else if (right_end_reached) {
if (left_level == 0) {
+ up_read(&fs_info->commit_root_sem);
ret = changed_cb(left_path, right_path,
&left_key,
BTRFS_COMPARE_TREE_NEW,
sctx);
if (ret < 0)
goto out;
+ down_read(&fs_info->commit_root_sem);
}
advance_left = ADVANCE;
continue;
}
if (left_level == 0 && right_level == 0) {
+ up_read(&fs_info->commit_root_sem);
cmp = btrfs_comp_cpu_keys(&left_key, &right_key);
if (cmp < 0) {
ret = changed_cb(left_path, right_path,
&left_key,
BTRFS_COMPARE_TREE_NEW,
sctx);
- if (ret < 0)
- goto out;
advance_left = ADVANCE;
} else if (cmp > 0) {
ret = changed_cb(left_path, right_path,
&right_key,
BTRFS_COMPARE_TREE_DELETED,
sctx);
- if (ret < 0)
- goto out;
advance_right = ADVANCE;
} else {
enum btrfs_compare_tree_result result;
result = BTRFS_COMPARE_TREE_SAME;
ret = changed_cb(left_path, right_path,
&left_key, result, sctx);
- if (ret < 0)
- goto out;
advance_left = ADVANCE;
advance_right = ADVANCE;
}
+
+ if (ret < 0)
+ goto out;
+ down_read(&fs_info->commit_root_sem);
} else if (left_level == right_level) {
cmp = btrfs_comp_cpu_keys(&left_key, &right_key);
if (cmp < 0) {
}
}
+out_unlock:
+ up_read(&fs_info->commit_root_sem);
out:
btrfs_free_path(left_path);
btrfs_free_path(right_path);
if (ret)
goto out;
- spin_lock(&fs_info->send_reloc_lock);
- if (test_bit(BTRFS_FS_RELOC_RUNNING, &fs_info->flags)) {
- spin_unlock(&fs_info->send_reloc_lock);
- btrfs_warn_rl(fs_info,
- "cannot run send because a relocation operation is in progress");
- ret = -EAGAIN;
- goto out;
- }
- fs_info->send_in_progress++;
- spin_unlock(&fs_info->send_reloc_lock);
-
ret = send_subvol(sctx);
- spin_lock(&fs_info->send_reloc_lock);
- fs_info->send_in_progress--;
- spin_unlock(&fs_info->send_reloc_lock);
if (ret < 0)
goto out;
projects / linux.git / commitdiff