Linux 6.13-rc4

[linux.git] / fs / btrfs / locking.c

// 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;
}

/*
 * 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);
}