path: root/fs/jbd2/revoke.c

// SPDX-License-Identifier: GPL-2.0+
/*
 * linux/fs/jbd2/revoke.c
 *
 * Written by Stephen C. Tweedie <sct@redhat.com>, 2000
 *
 * Copyright 2000 Red Hat corp --- All Rights Reserved
 *
 * Journal revoke routines for the generic filesystem journaling code;
 * part of the ext2fs journaling system.
 *
 * Revoke is the mechanism used to prevent old log records for deleted
 * metadata from being replayed on top of newer data using the same
 * blocks.  The revoke mechanism is used in two separate places:
 *
 * + Commit: during commit we write the entire list of the current
 *   transaction's revoked blocks to the journal
 *
 * + Recovery: during recovery we record the transaction ID of all
 *   revoked blocks.  If there are multiple revoke records in the log
 *   for a single block, only the last one counts, and if there is a log
 *   entry for a block beyond the last revoke, then that log entry still
 *   gets replayed.
 *
 * We can get interactions between revokes and new log data within a
 * single transaction:
 *
 * Block is revoked and then journaled:
 *   The desired end result is the journaling of the new block, so we
 *   cancel the revoke before the transaction commits.
 *
 * Block is journaled and then revoked:
 *   The revoke must take precedence over the write of the block, so we
 *   need either to cancel the journal entry or to write the revoke
 *   later in the log than the log block.  In this case, we choose the
 *   latter: journaling a block cancels any revoke record for that block
 *   in the current transaction, so any revoke for that block in the
 *   transaction must have happened after the block was journaled and so
 *   the revoke must take precedence.
 *
 * Block is revoked and then written as data:
 *   The data write is allowed to succeed, but the revoke is _not_
 *   cancelled.  We still need to prevent old log records from
 *   overwriting the new data.  We don't even need to clear the revoke
 *   bit here.
 *
 * We cache revoke status of a buffer in the current transaction in b_states
 * bits.  As the name says, revokevalid flag indicates that the cached revoke
 * status of a buffer is valid and we can rely on the cached status.
 *
 * Revoke information on buffers is a tri-state value:
 *
 * RevokeValid clear:	no cached revoke status, need to look it up
 * RevokeValid set, Revoked clear:
 *			buffer has not been revoked, and cancel_revoke
 *			need do nothing.
 * RevokeValid set, Revoked set:
 *			buffer has been revoked.
 *
 * Locking rules:
 * We keep two hash tables of revoke records. One hashtable belongs to the
 * running transaction (is pointed to by journal->j_revoke), the other one
 * belongs to the committing transaction. Accesses to the second hash table
 * happen only from the kjournald and no other thread touches this table.  Also
 * journal_switch_revoke_table() which switches which hashtable belongs to the
 * running and which to the committing transaction is called only from
 * kjournald. Therefore we need no locks when accessing the hashtable belonging
 * to the committing transaction.
 *
 * All users operating on the hash table belonging to the running transaction
 * have a handle to the transaction. Therefore they are safe from kjournald
 * switching hash tables under them. For operations on the lists of entries in
 * the hash table j_revoke_lock is used.
 *
 * Finally, also replay code uses the hash tables but at this moment no one else
 * can touch them (filesystem isn't mounted yet) and hence no locking is
 * needed.
 */

#ifndef __KERNEL__
#include "jfs_user.h"
#else
#include <linux/time.h>
#include <linux/fs.h>
#include <linux/jbd2.h>
#include <linux/errno.h>
#include <linux/slab.h>
#include <linux/list.h>
#include <linux/init.h>
#include <linux/bio.h>
#include <linux/log2.h>
#include <linux/hash.h>
#endif

static struct kmem_cache *jbd2_revoke_record_cache;
static struct kmem_cache *jbd2_revoke_table_cache;

/* Each revoke record represents one single revoked block.  During
   journal replay, this involves recording the transaction ID of the
   last transaction to revoke this block. */

struct jbd2_revoke_record_s
{
	struct list_head  hash;
	tid_t		  sequence;	/* Used for recovery only */
	unsigned long long	  blocknr;
};


/* The revoke table is just a simple hash table of revoke records. */
struct jbd2_revoke_table_s
{
	/* It is conceivable that we might want a larger hash table
	 * for recovery.  Must be a power of two. */
	int		  hash_size;
	int		  hash_shift;
	struct list_head *hash_table;
};


#ifdef __KERNEL__
static void write_one_revoke_record(transaction_t *,
				    struct list_head *,
				    struct buffer_head **, int *,
				    struct jbd2_revoke_record_s *);
static void flush_descriptor(journal_t *, struct buffer_head *, int);
#endif

/* Utility functions to maintain the revoke table */

static inline int hash(journal_t *journal, unsigned long long block)
{
	return hash_64(block, journal->j_revoke->hash_shift);
}

static int insert_revoke_hash(journal_t *journal, unsigned long long blocknr,
			      tid_t seq)
{
	struct list_head *hash_list;
	struct jbd2_revoke_record_s *record;
	gfp_t gfp_mask = GFP_NOFS;

	if (journal_oom_retry)
		gfp_mask |= __GFP_NOFAIL;
	record = kmem_cache_alloc(jbd2_revoke_record_cache, gfp_mask);
	if (!record)
		return -ENOMEM;

	record->sequence = seq;
	record->blocknr = blocknr;
	hash_list = &journal->j_revoke->hash_table[hash(journal, blocknr)];
	spin_lock(&journal->j_revoke_lock);
	list_add(&record->hash, hash_list);
	spin_unlock(&journal->j_revoke_lock);
	return 0;
}

/* Find a revoke record in the journal's hash table. */

static struct jbd2_revoke_record_s *find_revoke_record(journal_t *journal,
						      unsigned long long blocknr)
{
	struct list_head *hash_list;
	struct jbd2_revoke_record_s *record;

	hash_list = &journal->j_revoke->hash_table[hash(journal, blocknr)];

	spin_lock(&journal->j_revoke_lock);
	record = (struct jbd2_revoke_record_s *) hash_list->next;
	while (&(record->hash) != hash_list) {
		if (record->blocknr == blocknr) {
			spin_unlock(&journal->j_revoke_lock);
			return record;
		}
		record = (struct jbd2_revoke_record_s *) record->hash.next;
	}
	spin_unlock(&journal->j_revoke_lock);
	return NULL;
}

void jbd2_journal_destroy_revoke_record_cache(void)
{
	kmem_cache_destroy(jbd2_revoke_record_cache);
	jbd2_revoke_record_cache = NULL;
}

void jbd2_journal_destroy_revoke_table_cache(void)
{
	kmem_cache_destroy(jbd2_revoke_table_cache);
	jbd2_revoke_table_cache = NULL;
}

int __init jbd2_journal_init_revoke_record_cache(void)
{
	J_ASSERT(!jbd2_revoke_record_cache);
	jbd2_revoke_record_cache = KMEM_CACHE(jbd2_revoke_record_s,
					SLAB_HWCACHE_ALIGN|SLAB_TEMPORARY);

	if (!jbd2_revoke_record_cache) {
		pr_emerg("JBD2: failed to create revoke_record cache\n");
		return -ENOMEM;
	}
	return 0;
}

int __init jbd2_journal_init_revoke_table_cache(void)
{
	J_ASSERT(!jbd2_revoke_table_cache);
	jbd2_revoke_table_cache = KMEM_CACHE(jbd2_revoke_table_s,
					     SLAB_TEMPORARY);
	if (!jbd2_revoke_table_cache) {
		pr_emerg("JBD2: failed to create revoke_table cache\n");
		return -ENOMEM;
	}
	return 0;
}

static struct jbd2_revoke_table_s *jbd2_journal_init_revoke_table(int hash_size)
{
	int shift = 0;
	int tmp = hash_size;
	struct jbd2_revoke_table_s *table;

	table = kmem_cache_alloc(jbd2_revoke_table_cache, GFP_KERNEL);
	if (!table)
		goto out;

	while((tmp >>= 1UL) != 0UL)
		shift++;

	table->hash_size = hash_size;
	table->hash_shift = shift;
	table->hash_table =
		kmalloc_array(hash_size, sizeof(struct list_head), GFP_KERNEL);
	if (!table->hash_table) {
		kmem_cache_free(jbd2_revoke_table_cache, table);
		table = NULL;
		goto out;
	}

	for (tmp = 0; tmp < hash_size; tmp++)
		INIT_LIST_HEAD(&table->hash_table[tmp]);

out:
	return table;
}

static void jbd2_journal_destroy_revoke_table(struct jbd2_revoke_table_s *table)
{
	int i;
	struct list_head *hash_list;

	for (i = 0; i < table->hash_size; i++) {
		hash_list = &table->