v4.19.13 snapshot.
diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c
new file mode 100644
index 0000000..1da768e
--- /dev/null
+++ b/fs/btrfs/locking.c
@@ -0,0 +1,287 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2008 Oracle. All rights reserved.
+ */
+
+#include <linux/sched.h>
+#include <linux/pagemap.h>
+#include <linux/spinlock.h>
+#include <linux/page-flags.h>
+#include <asm/bug.h>
+#include "ctree.h"
+#include "extent_io.h"
+#include "locking.h"
+
+static void btrfs_assert_tree_read_locked(struct extent_buffer *eb);
+
+/*
+ * if we currently have a spinning reader or writer lock
+ * (indicated by the rw flag) this will bump the count
+ * of blocking holders and drop the spinlock.
+ */
+void btrfs_set_lock_blocking_rw(struct extent_buffer *eb, int rw)
+{
+ /*
+ * no lock is required. The lock owner may change if
+ * we have a read lock, but it won't change to or away
+ * from us. If we have the write lock, we are the owner
+ * and it'll never change.
+ */
+ if (eb->lock_nested && current->pid == eb->lock_owner)
+ return;
+ if (rw == BTRFS_WRITE_LOCK) {
+ if (atomic_read(&eb->blocking_writers) == 0) {
+ WARN_ON(atomic_read(&eb->spinning_writers) != 1);
+ atomic_dec(&eb->spinning_writers);
+ btrfs_assert_tree_locked(eb);
+ atomic_inc(&eb->blocking_writers);
+ write_unlock(&eb->lock);
+ }
+ } else if (rw == BTRFS_READ_LOCK) {
+ btrfs_assert_tree_read_locked(eb);
+ atomic_inc(&eb->blocking_readers);
+ WARN_ON(atomic_read(&eb->spinning_readers) == 0);
+ atomic_dec(&eb->spinning_readers);
+ read_unlock(&eb->lock);
+ }
+}
+
+/*
+ * if we currently have a blocking lock, take the spinlock
+ * and drop our blocking count
+ */
+void btrfs_clear_lock_blocking_rw(struct extent_buffer *eb, int rw)
+{
+ /*
+ * no lock is required. The lock owner may change if
+ * we have a read lock, but it won't change to or away
+ * from us. If we have the write lock, we are the owner
+ * and it'll never change.
+ */
+ if (eb->lock_nested && current->pid == eb->lock_owner)
+ return;
+
+ if (rw == BTRFS_WRITE_LOCK_BLOCKING) {
+ BUG_ON(atomic_read(&eb->blocking_writers) != 1);
+ write_lock(&eb->lock);
+ WARN_ON(atomic_read(&eb->spinning_writers));
+ atomic_inc(&eb->spinning_writers);
+ /* atomic_dec_and_test implies a barrier */
+ if (atomic_dec_and_test(&eb->blocking_writers))
+ cond_wake_up_nomb(&eb->write_lock_wq);
+ } else if (rw == BTRFS_READ_LOCK_BLOCKING) {
+ BUG_ON(atomic_read(&eb->blocking_readers) == 0);
+ read_lock(&eb->lock);
+ atomic_inc(&eb->spinning_readers);
+ /* atomic_dec_and_test implies a barrier */
+ if (atomic_dec_and_test(&eb->blocking_readers))
+ cond_wake_up_nomb(&eb->read_lock_wq);
+ }
+}
+
+/*
+ * take a spinning read lock. This will wait for any blocking
+ * writers
+ */
+void btrfs_tree_read_lock(struct extent_buffer *eb)
+{
+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) {
+ /*
+ * This extent is already write-locked by our thread. We allow
+ * an additional read lock to be added because it's for the same
+ * thread. btrfs_find_all_roots() depends on this as it may be
+ * called on a partly (write-)locked tree.
+ */
+ BUG_ON(eb->lock_nested);
+ eb->lock_nested = 1;
+ read_unlock(&eb->lock);
+ return;
+ }
+ if (atomic_read(&eb->blocking_writers)) {
+ read_unlock(&eb->lock);
+ wait_event(eb->write_lock_wq,
+ atomic_read(&eb->blocking_writers) == 0);
+ goto again;
+ }
+ atomic_inc(&eb->read_locks);
+ atomic_inc(&eb->spinning_readers);
+}
+
+/*
+ * take a spinning read lock.
+ * returns 1 if we get the read lock and 0 if we don't
+ * this won't wait for blocking writers
+ */
+int btrfs_tree_read_lock_atomic(struct extent_buffer *eb)
+{
+ if (atomic_read(&eb->blocking_writers))
+ return 0;
+
+ read_lock(&eb->lock);
+ if (atomic_read(&eb->blocking_writers)) {
+ read_unlock(&eb->lock);
+ return 0;
+ }
+ atomic_inc(&eb->read_locks);
+ atomic_inc(&eb->spinning_readers);
+ return 1;
+}
+
+/*
+ * returns 1 if we get the read lock and 0 if we don't
+ * this won't wait for blocking writers
+ */
+int btrfs_try_tree_read_lock(struct extent_buffer *eb)
+{
+ if (atomic_read(&eb->blocking_writers))
+ return 0;
+
+ if (!read_trylock(&eb->lock))
+ return 0;
+
+ if (atomic_read(&eb->blocking_writers)) {
+ read_unlock(&eb->lock);
+ return 0;
+ }
+ atomic_inc(&eb->read_locks);
+ atomic_inc(&eb->spinning_readers);
+ return 1;
+}
+
+/*
+ * returns 1 if we get the read lock and 0 if we don't
+ * this won't wait for blocking writers or readers
+ */
+int btrfs_try_tree_write_lock(struct extent_buffer *eb)
+{
+ if (atomic_read(&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)) {
+ write_unlock(&eb->lock);
+ return 0;
+ }
+ atomic_inc(&eb->write_locks);
+ atomic_inc(&eb->spinning_writers);
+ eb->lock_owner = current->pid;
+ return 1;
+}
+
+/*
+ * drop a spinning read lock
+ */
+void btrfs_tree_read_unlock(struct extent_buffer *eb)
+{
+ /*
+ * if we're nested, we have the write lock. No new locking
+ * is needed as long as we are the lock owner.
+ * The write unlock will do a barrier for us, and the lock_nested
+ * field only matters to the lock owner.
+ */
+ if (eb->lock_nested && current->pid == eb->lock_owner) {
+ eb->lock_nested = 0;
+ return;
+ }
+ btrfs_assert_tree_read_locked(eb);
+ WARN_ON(atomic_read(&eb->spinning_readers) == 0);
+ atomic_dec(&eb->spinning_readers);
+ atomic_dec(&eb->read_locks);
+ read_unlock(&eb->lock);
+}
+
+/*
+ * drop a blocking read lock
+ */
+void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb)
+{
+ /*
+ * if we're nested, we have the write lock. No new locking
+ * is needed as long as we are the lock owner.
+ * The write unlock will do a barrier for us, and the lock_nested
+ * field only matters to the lock owner.
+ */
+ if (eb->lock_nested && current->pid == eb->lock_owner) {
+ eb->lock_nested = 0;
+ return;
+ }
+ btrfs_assert_tree_read_locked(eb);
+ WARN_ON(atomic_read(&eb->blocking_readers) == 0);
+ /* atomic_dec_and_test implies a barrier */
+ if (atomic_dec_and_test(&eb->blocking_readers))
+ cond_wake_up_nomb(&eb->read_lock_wq);
+ atomic_dec(&eb->read_locks);
+}
+
+/*
+ * take a spinning write lock. This will wait for both
+ * blocking readers or writers
+ */
+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);
+ write_lock(&eb->lock);
+ if (atomic_read(&eb->blocking_readers)) {
+ write_unlock(&eb->lock);
+ wait_event(eb->read_lock_wq,
+ atomic_read(&eb->blocking_readers) == 0);
+ goto again;
+ }
+ if (atomic_read(&eb->blocking_writers)) {
+ write_unlock(&eb->lock);
+ wait_event(eb->write_lock_wq,
+ atomic_read(&eb->blocking_writers) == 0);
+ goto again;
+ }
+ WARN_ON(atomic_read(&eb->spinning_writers));
+ atomic_inc(&eb->spinning_writers);
+ atomic_inc(&eb->write_locks);
+ eb->lock_owner = current->pid;
+}
+
+/*
+ * drop a spinning or a blocking write lock.
+ */
+void btrfs_tree_unlock(struct extent_buffer *eb)
+{
+ int blockers = atomic_read(&eb->blocking_writers);
+
+ BUG_ON(blockers > 1);
+
+ btrfs_assert_tree_locked(eb);
+ eb->lock_owner = 0;
+ atomic_dec(&eb->write_locks);
+
+ if (blockers) {
+ WARN_ON(atomic_read(&eb->spinning_writers));
+ atomic_dec(&eb->blocking_writers);
+ /* Use the lighter barrier after atomic */
+ smp_mb__after_atomic();
+ cond_wake_up_nomb(&eb->write_lock_wq);
+ } else {
+ WARN_ON(atomic_read(&eb->spinning_writers) != 1);
+ atomic_dec(&eb->spinning_writers);
+ write_unlock(&eb->lock);
+ }
+}
+
+void btrfs_assert_tree_locked(struct extent_buffer *eb)
+{
+ BUG_ON(!atomic_read(&eb->write_locks));
+}
+
+static void btrfs_assert_tree_read_locked(struct extent_buffer *eb)
+{
+ BUG_ON(!atomic_read(&eb->read_locks));
+}