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bcachefs: Fix is_ancestor bitmap

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The is_ancestor bitmap is at optimization for bch2_snapshot_is_ancestor;
once we get sufficiently close to the ancestor ID we're searching for we
test a bitmap.

But initialization of the is_ancestor bitmap was broken; we do it by
using bch2_snapshot_parent(), but we call that on nodes that haven't
been initialized yet with bch2_mark_snapshot().

Fix this by adding a separate loop in bch2_snapshots_read() for
initializing the is_ancestor bitmap, and also add some new debug asserts
for checking this sort of breakage in the future.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This commit is contained in:
Kent Overstreet 2023-07-13 02:43:29 -04:00
parent fa5bed376a
commit 66487c54ad
1 changed files with 44 additions and 22 deletions
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66
fs/bcachefs/snapshot.c
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@ -88,6 +88,20 @@ static int bch2_snapshot_tree_create(struct btree_trans *trans,
/* Snapshot nodes: */
static bool bch2_snapshot_is_ancestor_early(struct bch_fs *c, u32 id, u32 ancestor)
{
struct snapshot_table *t;
rcu_read_lock();
t = rcu_dereference(c->snapshots);
while (id && id < ancestor)
id = __snapshot_t(t, id)->parent;
rcu_read_unlock();
return id == ancestor;
}
static inline u32 get_ancestor_below(struct snapshot_table *t, u32 id, u32 ancestor)
{
const struct snapshot_t *s = __snapshot_t(t, id);
@ -114,28 +128,19 @@ bool __bch2_snapshot_is_ancestor(struct bch_fs *c, u32 id, u32 ancestor)
while (id && id < ancestor - IS_ANCESTOR_BITMAP)
id = get_ancestor_below(t, id, ancestor);
ret = id && id < ancestor
? test_bit(ancestor - id - 1, __snapshot_t(t, id)->is_ancestor)
: id == ancestor;
if (id && id < ancestor) {
ret = test_bit(ancestor - id - 1, __snapshot_t(t, id)->is_ancestor);
EBUG_ON(ret != bch2_snapshot_is_ancestor_early(c, id, ancestor));
} else {
ret = id == ancestor;
}
rcu_read_unlock();
return ret;
}
static bool bch2_snapshot_is_ancestor_early(struct bch_fs *c, u32 id, u32 ancestor)
{
struct snapshot_table *t;
rcu_read_lock();
t = rcu_dereference(c->snapshots);
while (id && id < ancestor)
id = __snapshot_t(t, id)->parent;
rcu_read_unlock();
return id == ancestor;
}
struct snapshot_t_free_rcu {
struct rcu_head rcu;
struct snapshot_table *t;
@ -280,6 +285,23 @@ int bch2_snapshot_invalid(const struct bch_fs *c, struct bkey_s_c k,
return 0;
}
static void __set_is_ancestor_bitmap(struct bch_fs *c, u32 id)
{
struct snapshot_t *t = snapshot_t_mut(c, id);
u32 parent = id;
while ((parent = bch2_snapshot_parent_early(c, parent)) &&
parent - id - 1 < IS_ANCESTOR_BITMAP)
__set_bit(parent - id - 1, t->is_ancestor);
}
static void set_is_ancestor_bitmap(struct bch_fs *c, u32 id)
{
mutex_lock(&c->snapshot_table_lock);
__set_is_ancestor_bitmap(c, id);
mutex_unlock(&c->snapshot_table_lock);
}
int bch2_mark_snapshot(struct btree_trans *trans,
enum btree_id btree, unsigned level,
struct bkey_s_c old, struct bkey_s_c new,
@ -300,7 +322,6 @@ int bch2_mark_snapshot(struct btree_trans *trans,
if (new.k->type == KEY_TYPE_snapshot) {
struct bkey_s_c_snapshot s = bkey_s_c_to_snapshot(new);
u32 parent = id;
t->parent = le32_to_cpu(s.v->parent);
t->children[0] = le32_to_cpu(s.v->children[0]);
@ -320,9 +341,7 @@ int bch2_mark_snapshot(struct btree_trans *trans,
t->skip[2] = 0;
}
while ((parent = bch2_snapshot_parent_early(c, parent)) &&
parent - id - 1 < IS_ANCESTOR_BITMAP)
__set_bit(parent - id - 1, t->is_ancestor);
__set_is_ancestor_bitmap(c, id);
if (BCH_SNAPSHOT_DELETED(s.v)) {
set_bit(BCH_FS_HAVE_DELETED_SNAPSHOTS, &c->flags);
@ -1380,7 +1399,10 @@ int bch2_snapshots_read(struct bch_fs *c)
for_each_btree_key2(&trans, iter, BTREE_ID_snapshots,
POS_MIN, 0, k,
bch2_mark_snapshot(&trans, BTREE_ID_snapshots, 0, bkey_s_c_null, k, 0) ?:
bch2_snapshot_set_equiv(&trans, k)));
bch2_snapshot_set_equiv(&trans, k)) ?:
for_each_btree_key2(&trans, iter, BTREE_ID_snapshots,
POS_MIN, 0, k,
(set_is_ancestor_bitmap(c, k.k->p.offset), 0)));
if (ret)
bch_err_fn(c, ret);
return ret;