// 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 <trace/events/btrfs.h>
#include "misc.h"
#include "ctree.h"
#include "extent_io.h"
#include "locking.h"
/*
* Lockdep class keys for extent_buffer->lock's in this root. For a given
* eb, the lockdep key is determined by the btrfs_root it belongs to and
* the level the eb occupies in the tree.
*
* Different roots are used for different purposes and may nest inside each
* other and they require separate keysets. As lockdep keys should be
* static, assign keysets according to the purpose of the root as indicated
* by btrfs_root->root_key.objectid. This ensures that all special purpose
* roots have separate keysets.
*
* Lock-nesting across peer nodes is always done with the immediate parent
* node locked thus preventing deadlock. As lockdep doesn't know this, use
* subclass to avoid triggering lockdep warning in such cases.
*
* The key is set by the readpage_end_io_hook after the buffer has passed
* csum validation but before the pages are unlocked. It is also set by
* btrfs_init_new_buffer on freshly allocated blocks.
*
* We also add a check to make sure the highest level of the tree is the
* same as our lockdep setup here. If BTRFS_MAX_LEVEL changes, this code
* needs update as well.
*/
#ifdef CONFIG_DEBUG_LOCK_ALLOC
#if BTRFS_MAX_LEVEL != 8
#error
#endif
#define DEFINE_LEVEL(stem, level) \
.names[level] = "btrfs-" stem "-0" #level,
#define DEFINE_NAME(stem) \
DEFINE_LEVEL(stem, 0) \
DEFINE_LEVEL(stem, 1) \
DEFINE_LEVEL(stem, 2) \
DEFINE_LEVEL(stem, 3) \
DEFINE_LEVEL(stem, 4) \
DEFINE_LEVEL(stem, 5) \
DEFINE_LEVEL(stem, 6) \
DEFINE_LEVEL(stem, 7)
static struct btrfs_lockdep_keyset {
u64 id; /* root objectid */
/* Longest entry: btrfs-block-group-00 */
char names[BTRFS_MAX_LEVEL][24];
struct lock_class_key keys[BTRFS_MAX_LEVEL];
} btrfs_lockdep_keysets[] = {
{ .id = BTRFS_ROOT_TREE_OBJECTID, DEFINE_NAME("root") },
{ .id = BTRFS_EXTENT_TREE_OBJECTID, DEFINE_NAME("extent") },
{ .id = BTRFS_CHUNK_TREE_OBJECTID, DEFINE_NAME("chunk") },
{ .id = BTRFS_DEV_TREE_OBJECTID, DEFINE_NAME("dev") },
{ .id = BTRFS_CSUM_TREE_OBJECTID, DEFINE_NAME("csum") },
{ .id = BTRFS_QUOTA_TREE_OBJECTID, DEFINE_NAME("quota") },
{ .id = BTRFS_TREE_LOG_OBJECTID, DEFINE_NAME("log") },
{ .id = BTRFS_TREE_RELOC_OBJECTID, DEFINE_NAME("treloc") },
{ .id = BTRFS_DATA_RELOC_TREE_OBJECTID, DEFINE_NAME("dreloc") },
{ .id = BTRFS_UUID_TREE_OBJECTID, DEFINE_NAME("uuid") },
{ .id = BTRFS_FREE_SPACE_TREE_OBJECTID, DEFINE_NAME("free-space") },
{ .id = BTRFS_BLOCK_GROUP_TREE_OBJECTID, DEFINE_NAME("block-group") },
{ .id = BTRFS_RAID_STRIPE_TREE_OBJECTID, DEFINE_NAME("raid-stripe") },
{ .id = 0, DEFINE_NAME("tree") },
};
#undef DEFINE_LEVEL
#undef DEFINE_NAME
void btrfs_set_buffer_lockdep_class(u64 objectid, struct extent_buffer *eb, int level)
{
struct btrfs_lockdep_keyset *ks;
ASSERT(level < ARRAY_SIZE(ks->keys));
/* Find the matching keyset, id 0 is the default entry */
for (ks = btrfs_lockdep_keysets; ks->id; ks++)
if (ks->id == objectid)
break;
lockdep_set_class_and_name(&eb->lock, &ks->keys[level], ks->names[level]);
}
void btrfs_maybe_reset_lockdep_class(struct btrfs_root *root, struct extent_buffer *eb)
{
if (test_bit(BTRFS_ROOT_RESET_LOCKDEP_CLASS, &root->state))
btrfs_set_buffer_lockdep_class(btrfs_root_id(root),
eb, btrfs_header_level(eb));
}
#endif
#ifdef CONFIG_BTRFS_DEBUG
static void btrfs_set_eb_lock_owner(struct extent_buffer *eb, pid_t owner)
{
eb->lock_owner = owner;
}
#else
static void btrfs_set_eb_lock_owner(struct extent_buffer *eb, pid_t owner) { }
#endif
/*
* Extent buffer locking
* =====================
*
* We use a rw_semaphore for tree locking, and the semantics are exactly the
* same:
*
* - reader/writer exclusion
* - writer/writer exclusion
* - reader/reader sharing
* - try-lock semantics for readers and writers
*
* The rwsem implementation does opportunistic spinning which reduces number of
* times the locking task needs to sleep.
*/
/*
* btrfs_tree_read_lock_nested - lock extent buffer for read
* @eb: the eb to be locked
* @nest: the nesting level to be used for lockdep
*
* This takes the read lock on the extent buffer, using the specified nesting
* level for lockdep purposes.
*/
void btrfs_tree_read_lock_nested(struct extent_buffer *eb, enum btrfs_lock_nesting nest)
{
u64 start_ns = 0;
if (trace_btrfs_tree_read_lock_enabled())
start_ns = ktime_get_ns();
down_read_nested(&eb->lock, nest);
trace_btrfs_tree_read_lock(eb, start_ns);
}
/*
* Try-lock for read.
*
* Return 1 if the rwlock has been taken, 0 otherwise
*/
int btrfs_try_tree_read_lock(struct extent_buffer *eb)
{
if (down_read_trylock(&eb->lock)) {
trace_btrfs_try_tree_read_lock(eb);
return 1;
}
return 0;
}
/*
* Try-lock for write.
*
* Return 1 if the rwlock has been taken, 0 otherwise
*/
int btrfs_try_tree_write_lock(struct extent_buffer *eb)
{
if (down_write_trylock(&eb->lock)) {
btrfs_set_eb_lock_owner(eb, current->pid);
trace_btrfs_try_tree_write_lock(eb);
return 1;
}
return 0;
}
/*
* Release read lock.
*/
void btrfs_tree_read_unlock(struct extent_buffer *eb)
{
trace_btrfs_tree_read_unlock(eb);
up_read(&eb->lock);
}
/*
* Lock eb for write.
*
* @eb: the eb to lock
* @nest: the nesting to use for the lock
*
* Returns with the eb->lock write locked.
*/
void btrfs_tree_lock_nested(struct extent_buffer *eb, enum btrfs_lock_nesting nest)
__acquires(&eb->lock)
{
u64 start_ns = 0;
if (trace_btrfs_tree_lock_enabled())
start_ns = ktime_get_ns();
down_write_nested(&eb->lock, nest);
btrfs_set_eb_lock_owner(eb, current->pid);
trace_btrfs_tree_lock(eb, start_ns);
}
/*
* Release the write lock.
*/
void btrfs_tree_unlock(struct extent_buffer *eb)
{
trace_btrfs_tree_unlock(eb);
btrfs_set_eb_lock_owner(eb, 0);
up_write(&eb->lock);
}
/*
* This releases any locks held in the path starting at level and going all the
* way up to the root.
*
* btrfs_search_slot will keep the lock held on higher nodes in a few corner
* cases, such as COW of the block at slot zero in the node. This ignores
* those rules, and it should only be called when there are no more updates to
* be done higher up in the tree.
*/
void btrfs_unlock_up_safe(struct btrfs_path *path, int level)
{
int i;
if (path->keep_locks)
return;
for (i = level; i < BTRFS_MAX_LEVEL; i++) {
if (!path->nodes[i])
continue;
if (!path->locks[i])
continue;
btrfs_tree_unlock_rw(path->nodes[i], path->locks[i]);
path->locks[i] = 0;
}
}
/*
* Loop around taking references on and locking the root node of the tree until
* we end up with a lock on the root node.
*
* Return: root extent buffer with write lock held
*/
struct extent_buffer *btrfs_lock_root_node(struct btrfs_root *root)
{
struct extent_buffer *eb;
while (1) {
eb = btrfs_root_node(root);
btrfs_maybe_reset_lockdep_class(root, eb);
btrfs_tree_lock(eb);
if (eb == root->node)
break;
btrfs_tree_unlock(eb);
free_extent_buffer(eb);
}
return eb;
}
/*
* Loop around taking references on and locking the root node of the tree until
* we end up with a lock on the root node.
*
* Return: root extent buffer with read lock held
*/
struct extent_buffer *btrfs_read_lock_root_node(struct btrfs_root *root)
{
struct extent_buffer *eb;
while (1) {
eb = btrfs_root_node(root);
btrfs_maybe_reset_lockdep_class(root, eb);
btrfs_tree_read_lock(eb);
if (eb == root->node)
break;
btrfs_tree_read_unlock(eb);
free_extent_buffer(eb);
}
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 -EAGAIN.
*/
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)) {
free_extent_buffer(eb);
return ERR_PTR(-EAGAIN);
}
if (eb == root->node)
break;
btrfs_tree_read_unlock(eb);
free_extent_buffer(eb);
}
return eb;
}
/*
* DREW locks
* ==========
*
* DREW stands for double-reader-writer-exclusion lock. It's used in situation
* where you want to provide A-B exclusion but not AA or BB.
*
* Currently implementation gives more priority to reader. If a reader and a
* writer both race to acquire their respective sides of the lock the writer
* would yield its lock as soon as it detects a concurrent reader. Additionally
* if there are pending readers no new writers would be allowed to come in and
* acquire the lock.
*/
void btrfs_drew_lock_init(struct btrfs_drew_lock *lock)
{
atomic_set(&lock->readers, 0);
atomic_set(&lock->writers, 0);
init_waitqueue_head(&lock->pending_readers);
init_waitqueue_head(&lock->pending_writers);
}
/* Return true if acquisition is successful, false otherwise */
bool btrfs_drew_try_write_lock(struct btrfs_drew_lock *lock)
{
if (atomic_read(&lock->readers))
return false;
atomic_inc(&lock->writers);
/* Ensure writers count is updated before we check for pending readers */
smp_mb__after_atomic();
if (atomic_read(&lock->readers)) {
btrfs_drew_write_unlock(lock);
return false;
}
return true;
}
void btrfs_drew_write_lock(struct btrfs_drew_lock *lock)
{
while (true) {
if (btrfs_drew_try_write_lock(lock))
return;
wait_event(lock->pending_writers, !atomic_read(&lock->readers));
}
}
void btrfs_drew_write_unlock(struct btrfs_drew_lock *lock)
{
/*
* atomic_dec_and_test() implies a full barrier, so woken up readers are
* guaranteed to see the decrement.
*/
if (atomic_dec_and_test(&lock->writers))
wake_up(&lock->pending_readers);
}
void btrfs_drew_read_lock(struct btrfs_drew_lock *lock)
{
atomic_inc(&lock->readers);
/*
* Ensure the pending reader count is perceieved BEFORE this reader
* goes to sleep in case of active writers. This guarantees new writers
* won't be allowed and that the current reader will be woken up when
* the last active writer finishes its jobs.
*/
smp_mb__after_atomic();
wait_event(lock->pending_readers, atomic_read(&lock->writers) == 0);
}
void btrfs_drew_read_unlock(struct btrfs_drew_lock *lock)
{
/*
* atomic_dec_and_test implies a full barrier, so woken up writers
* are guaranteed to see the decrement
*/
if (atomic_dec_and_test(&lock->readers))
wake_up(&lock->pending_writers);
}
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