| Message ID | 20220912192752.3785061-3-shr@fb.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | io-uring/btrfs: support async buffered writes | expand |
On Mon, Sep 12, 2022 at 12:27:42PM -0700, Stefan Roesch wrote: > From: Josef Bacik <josef@toxicpanda.com> > > For NOWAIT IOCB's we'll need a way to tell search to not wait on locks > or anything. Accomplish this by adding a path->nowait flag that will > use trylocks and skip reading of metadata, returning -EAGAIN in either > of these cases. For now we only need this for reads, so only the read > side is handled. Add an ASSERT() to catch anybody trying to use this > for writes so they know they'll have to implement the write side. > > Signed-off-by: Josef Bacik <josef@toxicpanda.com> > Signed-off-by: Stefan Roesch <shr@fb.com> > --- > fs/btrfs/ctree.c | 39 ++++++++++++++++++++++++++++++++++++--- > fs/btrfs/ctree.h | 1 + > fs/btrfs/locking.c | 23 +++++++++++++++++++++++ > fs/btrfs/locking.h | 1 + > 4 files changed, 61 insertions(+), 3 deletions(-) > > diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c > index ebfa35fe1c38..71b238364939 100644 > --- a/fs/btrfs/ctree.c > +++ b/fs/btrfs/ctree.c > @@ -1447,6 +1447,11 @@ read_block_for_search(struct btrfs_root *root, struct btrfs_path *p, > return 0; > } > > + if (p->nowait) { > + free_extent_buffer(tmp); > + return -EAGAIN; > + } > + > if (unlock_up) > btrfs_unlock_up_safe(p, level + 1); > > @@ -1467,6 +1472,8 @@ read_block_for_search(struct btrfs_root *root, struct btrfs_path *p, > ret = -EAGAIN; > > goto out; > + } else if (p->nowait) { > + return -EAGAIN; > } > > if (unlock_up) { > @@ -1634,7 +1641,13 @@ static struct extent_buffer *btrfs_search_slot_get_root(struct btrfs_root *root, > * We don't know the level of the root node until we actually > * have it read locked > */ > - b = btrfs_read_lock_root_node(root); > + if (p->nowait) { > + b = btrfs_try_read_lock_root_node(root); > + if (IS_ERR(b)) > + return b; > + } else { > + b = btrfs_read_lock_root_node(root); > + } > level = btrfs_header_level(b); > if (level > write_lock_level) > goto out; > @@ -1910,6 +1923,13 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root *root, > WARN_ON(p->nodes[0] != NULL); > BUG_ON(!cow && ins_len); > > + /* > + * For now only allow nowait for read only operations. There's no > + * strict reason why we can't, we just only need it for reads so I'm > + * only implementing it for reads right now. > + */ > + ASSERT(!p->nowait || !cow); > + > if (ins_len < 0) { > lowest_unlock = 2; > > @@ -1936,7 +1956,12 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root *root, > > if (p->need_commit_sem) { > ASSERT(p->search_commit_root); > - down_read(&fs_info->commit_root_sem); > + if (p->nowait) { > + if (!down_read_trylock(&fs_info->commit_root_sem)) > + return -EAGAIN; > + } else { > + down_read(&fs_info->commit_root_sem); > + } > } > > again: > @@ -2082,7 +2107,15 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root *root, > btrfs_tree_lock(b); > p->locks[level] = BTRFS_WRITE_LOCK; > } else { > - btrfs_tree_read_lock(b); > + if (p->nowait) { > + if (!btrfs_try_tree_read_lock(b)) { > + free_extent_buffer(b); > + ret = -EAGAIN; > + goto done; > + } > + } else { > + btrfs_tree_read_lock(b); > + } > p->locks[level] = BTRFS_READ_LOCK; > } > p->nodes[level] = b; > diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h > index df8c99c99df9..ca59ba6421a9 100644 > --- a/fs/btrfs/ctree.h > +++ b/fs/btrfs/ctree.h > @@ -443,6 +443,7 @@ struct btrfs_path { > * header (ie. sizeof(struct btrfs_item) is not included). > */ > unsigned int search_for_extension:1; > + unsigned int nowait:1; > }; > #define BTRFS_MAX_EXTENT_ITEM_SIZE(r) ((BTRFS_LEAF_DATA_SIZE(r->fs_info) >> 4) - \ > sizeof(struct btrfs_item)) > diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c > index 9063072b399b..d6c88922d3e2 100644 > --- a/fs/btrfs/locking.c > +++ b/fs/btrfs/locking.c > @@ -285,6 +285,29 @@ struct extent_buffer *btrfs_read_lock_root_node(struct btrfs_root *root) > return eb; > } > > +/* > + * Loop around taking references on and locking the root node of the tree in > + * nowait mode until we end up with a lock on the root node or returning to > + * avoid blocking. > + * > + * Return: root extent buffer with read lock held or -EWOULDBLOCK. > + */ > +struct extent_buffer *btrfs_try_read_lock_root_node(struct btrfs_root *root) > +{ > + struct extent_buffer *eb; > + > + while (1) { > + eb = btrfs_root_node(root); > + if (!btrfs_try_tree_read_lock(eb)) > + return ERR_PTR(-EAGAIN); There's a leak of the extent buffer here. This fixes it up: diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c index 9d53bcfb6d9b..0eab3cb274a1 100644 --- a/fs/btrfs/locking.c +++ b/fs/btrfs/locking.c @@ -298,8 +298,10 @@ struct extent_buffer *btrfs_try_read_lock_root_node(struct btrfs_root *root) while (1) { eb = btrfs_root_node(root); - if (!btrfs_try_tree_read_lock(eb)) + if (!btrfs_try_tree_read_lock(eb)) { + free_extent_buffer(eb); return ERR_PTR(-EAGAIN); + } if (eb == root->node) break; btrfs_tree_read_unlock(eb); Thanks. > + if (eb == root->node) > + break; > + btrfs_tree_read_unlock(eb); > + free_extent_buffer(eb); > + } > + return eb; > +} > + > /* > * DREW locks > * ========== > diff --git a/fs/btrfs/locking.h b/fs/btrfs/locking.h > index ab268be09bb5..490c7a79e995 100644 > --- a/fs/btrfs/locking.h > +++ b/fs/btrfs/locking.h > @@ -94,6 +94,7 @@ int btrfs_try_tree_read_lock(struct extent_buffer *eb); > int btrfs_try_tree_write_lock(struct extent_buffer *eb); > struct extent_buffer *btrfs_lock_root_node(struct btrfs_root *root); > struct extent_buffer *btrfs_read_lock_root_node(struct btrfs_root *root); > +struct extent_buffer *btrfs_try_read_lock_root_node(struct btrfs_root *root); > > #ifdef CONFIG_BTRFS_DEBUG > static inline void btrfs_assert_tree_write_locked(struct extent_buffer *eb) > -- > 2.30.2 >
On Mon, Sep 26, 2022 at 10:14:40AM +0100, Filipe Manana wrote: > On Mon, Sep 12, 2022 at 12:27:42PM -0700, Stefan Roesch wrote: > > From: Josef Bacik <josef@toxicpanda.com> > > +{ > > + struct extent_buffer *eb; > > + > > + while (1) { > > + eb = btrfs_root_node(root); > > + if (!btrfs_try_tree_read_lock(eb)) > > + return ERR_PTR(-EAGAIN); > > There's a leak of the extent buffer here. > This fixes it up: > > diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c > index 9d53bcfb6d9b..0eab3cb274a1 100644 > --- a/fs/btrfs/locking.c > +++ b/fs/btrfs/locking.c > @@ -298,8 +298,10 @@ struct extent_buffer *btrfs_try_read_lock_root_node(struct btrfs_root *root) > > while (1) { > eb = btrfs_root_node(root); > - if (!btrfs_try_tree_read_lock(eb)) > + if (!btrfs_try_tree_read_lock(eb)) { > + free_extent_buffer(eb); > return ERR_PTR(-EAGAIN); > + } > if (eb == root->node) > break; > btrfs_tree_read_unlock(eb); Folded to the commit, thanks.
diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c index ebfa35fe1c38..71b238364939 100644 --- a/fs/btrfs/ctree.c +++ b/fs/btrfs/ctree.c @@ -1447,6 +1447,11 @@ read_block_for_search(struct btrfs_root *root, struct btrfs_path *p, return 0; } + if (p->nowait) { + free_extent_buffer(tmp); + return -EAGAIN; + } + if (unlock_up) btrfs_unlock_up_safe(p, level + 1); @@ -1467,6 +1472,8 @@ read_block_for_search(struct btrfs_root *root, struct btrfs_path *p, ret = -EAGAIN; goto out; + } else if (p->nowait) { + return -EAGAIN; } if (unlock_up) { @@ -1634,7 +1641,13 @@ static struct extent_buffer *btrfs_search_slot_get_root(struct btrfs_root *root, * We don't know the level of the root node until we actually * have it read locked */ - b = btrfs_read_lock_root_node(root); + if (p->nowait) { + b = btrfs_try_read_lock_root_node(root); + if (IS_ERR(b)) + return b; + } else { + b = btrfs_read_lock_root_node(root); + } level = btrfs_header_level(b); if (level > write_lock_level) goto out; @@ -1910,6 +1923,13 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root *root, WARN_ON(p->nodes[0] != NULL); BUG_ON(!cow && ins_len); + /* + * For now only allow nowait for read only operations. There's no + * strict reason why we can't, we just only need it for reads so I'm + * only implementing it for reads right now. + */ + ASSERT(!p->nowait || !cow); + if (ins_len < 0) { lowest_unlock = 2; @@ -1936,7 +1956,12 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root *root, if (p->need_commit_sem) { ASSERT(p->search_commit_root); - down_read(&fs_info->commit_root_sem); + if (p->nowait) { + if (!down_read_trylock(&fs_info->commit_root_sem)) + return -EAGAIN; + } else { + down_read(&fs_info->commit_root_sem); + } } again: @@ -2082,7 +2107,15 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root *root, btrfs_tree_lock(b); p->locks[level] = BTRFS_WRITE_LOCK; } else { - btrfs_tree_read_lock(b); + if (p->nowait) { + if (!btrfs_try_tree_read_lock(b)) { + free_extent_buffer(b); + ret = -EAGAIN; + goto done; + } + } else { + btrfs_tree_read_lock(b); + } p->locks[level] = BTRFS_READ_LOCK; } p->nodes[level] = b; diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h index df8c99c99df9..ca59ba6421a9 100644 --- a/fs/btrfs/ctree.h +++ b/fs/btrfs/ctree.h @@ -443,6 +443,7 @@ struct btrfs_path { * header (ie. sizeof(struct btrfs_item) is not included). */ unsigned int search_for_extension:1; + unsigned int nowait:1; }; #define BTRFS_MAX_EXTENT_ITEM_SIZE(r) ((BTRFS_LEAF_DATA_SIZE(r->fs_info) >> 4) - \ sizeof(struct btrfs_item)) diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c index 9063072b399b..d6c88922d3e2 100644 --- a/fs/btrfs/locking.c +++ b/fs/btrfs/locking.c @@ -285,6 +285,29 @@ struct extent_buffer *btrfs_read_lock_root_node(struct btrfs_root *root) return eb; } +/* + * Loop around taking references on and locking the root node of the tree in + * nowait mode until we end up with a lock on the root node or returning to + * avoid blocking. + * + * Return: root extent buffer with read lock held or -EWOULDBLOCK. + */ +struct extent_buffer *btrfs_try_read_lock_root_node(struct btrfs_root *root) +{ + struct extent_buffer *eb; + + while (1) { + eb = btrfs_root_node(root); + if (!btrfs_try_tree_read_lock(eb)) + return ERR_PTR(-EAGAIN); + if (eb == root->node) + break; + btrfs_tree_read_unlock(eb); + free_extent_buffer(eb); + } + return eb; +} + /* * DREW locks * ========== diff --git a/fs/btrfs/locking.h b/fs/btrfs/locking.h index ab268be09bb5..490c7a79e995 100644 --- a/fs/btrfs/locking.h +++ b/fs/btrfs/locking.h @@ -94,6 +94,7 @@ int btrfs_try_tree_read_lock(struct extent_buffer *eb); int btrfs_try_tree_write_lock(struct extent_buffer *eb); struct extent_buffer *btrfs_lock_root_node(struct btrfs_root *root); struct extent_buffer *btrfs_read_lock_root_node(struct btrfs_root *root); +struct extent_buffer *btrfs_try_read_lock_root_node(struct btrfs_root *root); #ifdef CONFIG_BTRFS_DEBUG static inline void btrfs_assert_tree_write_locked(struct extent_buffer *eb)