From 06297d8cefcaa2029c4cb71b79285d2bfff06d4d Mon Sep 17 00:00:00 2001 From: David Sterba Date: Thu, 2 May 2019 16:47:23 +0200 Subject: [PATCH] btrfs: switch extent_buffer blocking_writers from atomic to int The blocking_writers is either 0 or 1 and always updated under the lock, so we don't need the atomic_t semantics. Reviewed-by: Nikolay Borisov Signed-off-by: David Sterba --- fs/btrfs/extent_io.c | 2 +- fs/btrfs/extent_io.h | 2 +- fs/btrfs/locking.c | 46 +++++++++++++++++++------------------------ fs/btrfs/print-tree.c | 2 +- 4 files changed, 23 insertions(+), 29 deletions(-) diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index 43761ecd1201..6c49db9bfcf1 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -4857,7 +4857,7 @@ __alloc_extent_buffer(struct btrfs_fs_info *fs_info, u64 start, eb->bflags = 0; rwlock_init(&eb->lock); atomic_set(&eb->blocking_readers, 0); - atomic_set(&eb->blocking_writers, 0); + eb->blocking_writers = 0; eb->lock_nested = false; init_waitqueue_head(&eb->write_lock_wq); init_waitqueue_head(&eb->read_lock_wq); diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h index aa18a16a6ed7..201da61dfc21 100644 --- a/fs/btrfs/extent_io.h +++ b/fs/btrfs/extent_io.h @@ -167,7 +167,7 @@ struct extent_buffer { struct rcu_head rcu_head; pid_t lock_owner; - atomic_t blocking_writers; + int blocking_writers; atomic_t blocking_readers; bool lock_nested; /* >= 0 if eb belongs to a log tree, -1 otherwise */ diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c index 2f6c3c7851ed..5feb01147e19 100644 --- a/fs/btrfs/locking.c +++ b/fs/btrfs/locking.c @@ -111,10 +111,10 @@ void btrfs_set_lock_blocking_write(struct extent_buffer *eb) */ if (eb->lock_nested && current->pid == eb->lock_owner) return; - if (atomic_read(&eb->blocking_writers) == 0) { + if (eb->blocking_writers == 0) { btrfs_assert_spinning_writers_put(eb); btrfs_assert_tree_locked(eb); - atomic_inc(&eb->blocking_writers); + eb->blocking_writers++; write_unlock(&eb->lock); } } @@ -148,12 +148,11 @@ void btrfs_clear_lock_blocking_write(struct extent_buffer *eb) */ if (eb->lock_nested && current->pid == eb->lock_owner) return; - BUG_ON(atomic_read(&eb->blocking_writers) != 1); write_lock(&eb->lock); + BUG_ON(eb->blocking_writers != 1); btrfs_assert_spinning_writers_get(eb); - /* atomic_dec_and_test implies a barrier */ - if (atomic_dec_and_test(&eb->blocking_writers)) - cond_wake_up_nomb(&eb->write_lock_wq); + if (--eb->blocking_writers == 0) + cond_wake_up(&eb->write_lock_wq); } /* @@ -167,12 +166,10 @@ void btrfs_tree_read_lock(struct extent_buffer *eb) if (trace_btrfs_tree_read_lock_enabled()) start_ns = ktime_get_ns(); again: - BUG_ON(!atomic_read(&eb->blocking_writers) && - current->pid == eb->lock_owner); - read_lock(&eb->lock); - if (atomic_read(&eb->blocking_writers) && - current->pid == eb->lock_owner) { + BUG_ON(eb->blocking_writers == 0 && + current->pid == eb->lock_owner); + if (eb->blocking_writers && current->pid == eb->lock_owner) { /* * This extent is already write-locked by our thread. We allow * an additional read lock to be added because it's for the same @@ -185,10 +182,10 @@ again: trace_btrfs_tree_read_lock(eb, start_ns); return; } - if (atomic_read(&eb->blocking_writers)) { + if (eb->blocking_writers) { read_unlock(&eb->lock); wait_event(eb->write_lock_wq, - atomic_read(&eb->blocking_writers) == 0); + eb->blocking_writers == 0); goto again; } btrfs_assert_tree_read_locks_get(eb); @@ -203,11 +200,11 @@ again: */ int btrfs_tree_read_lock_atomic(struct extent_buffer *eb) { - if (atomic_read(&eb->blocking_writers)) + if (eb->blocking_writers) return 0; read_lock(&eb->lock); - if (atomic_read(&eb->blocking_writers)) { + if (eb->blocking_writers) { read_unlock(&eb->lock); return 0; } @@ -223,13 +220,13 @@ int btrfs_tree_read_lock_atomic(struct extent_buffer *eb) */ int btrfs_try_tree_read_lock(struct extent_buffer *eb) { - if (atomic_read(&eb->blocking_writers)) + if (eb->blocking_writers) return 0; if (!read_trylock(&eb->lock)) return 0; - if (atomic_read(&eb->blocking_writers)) { + if (eb->blocking_writers) { read_unlock(&eb->lock); return 0; } @@ -245,13 +242,11 @@ int btrfs_try_tree_read_lock(struct extent_buffer *eb) */ int btrfs_try_tree_write_lock(struct extent_buffer *eb) { - if (atomic_read(&eb->blocking_writers) || - atomic_read(&eb->blocking_readers)) + if (eb->blocking_writers || atomic_read(&eb->blocking_readers)) return 0; write_lock(&eb->lock); - if (atomic_read(&eb->blocking_writers) || - atomic_read(&eb->blocking_readers)) { + if (eb->blocking_writers || atomic_read(&eb->blocking_readers)) { write_unlock(&eb->lock); return 0; } @@ -322,10 +317,9 @@ void btrfs_tree_lock(struct extent_buffer *eb) WARN_ON(eb->lock_owner == current->pid); again: wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers) == 0); - wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0); + wait_event(eb->write_lock_wq, eb->blocking_writers == 0); write_lock(&eb->lock); - if (atomic_read(&eb->blocking_readers) || - atomic_read(&eb->blocking_writers)) { + if (atomic_read(&eb->blocking_readers) || eb->blocking_writers) { write_unlock(&eb->lock); goto again; } @@ -340,7 +334,7 @@ again: */ void btrfs_tree_unlock(struct extent_buffer *eb) { - int blockers = atomic_read(&eb->blocking_writers); + int blockers = eb->blocking_writers; BUG_ON(blockers > 1); @@ -351,7 +345,7 @@ void btrfs_tree_unlock(struct extent_buffer *eb) if (blockers) { btrfs_assert_no_spinning_writers(eb); - atomic_dec(&eb->blocking_writers); + eb->blocking_writers--; /* Use the lighter barrier after atomic */ smp_mb__after_atomic(); cond_wake_up_nomb(&eb->write_lock_wq); diff --git a/fs/btrfs/print-tree.c b/fs/btrfs/print-tree.c index 1141ca5fae6a..7cb4f1fbe043 100644 --- a/fs/btrfs/print-tree.c +++ b/fs/btrfs/print-tree.c @@ -155,7 +155,7 @@ static void print_eb_refs_lock(struct extent_buffer *eb) "refs %u lock (w:%d r:%d bw:%d br:%d sw:%d sr:%d) lock_owner %u current %u", atomic_read(&eb->refs), atomic_read(&eb->write_locks), atomic_read(&eb->read_locks), - atomic_read(&eb->blocking_writers), + eb->blocking_writers, atomic_read(&eb->blocking_readers), atomic_read(&eb->spinning_writers), atomic_read(&eb->spinning_readers), -- 2.30.2