jbd: update locking coments

[linux-2.6/libata-dev.git] / fs / jbd / revoke.c

/*
 * linux/fs/jbd/revoke.c
 *
 * Written by Stephen C. Tweedie <sct@redhat.com>, 2000
 *
 * Copyright 2000 Red Hat corp --- All Rights Reserved
 *
 * This file is part of the Linux kernel and is made available under
 * the terms of the GNU General Public License, version 2, or at your
 * option, any later version, incorporated herein by reference.
 *
 * 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.
 *
 * 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 *                      buffer has not been revoked, and cancel_revoke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 noone 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/jbd.h>
#include <linux/errno.h>
#include <linux/slab.h>
#include <linux/list.h>
#include <linux/init.h>
#endif
#include <linux/log2.h>

static struct kmem_cache *revoke_record_cache;
static struct kmem_cache *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 jbd_revoke_record_s
{
        struct list_head  hash;
        tid_t             sequence;     /* Used for recovery only */
        unsigned long     blocknr;
};


/* The revoke table is just a simple hash table of revoke records. */
struct jbd_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(journal_t *, transaction_t *,
                                    struct journal_head **, int *,
                                    struct jbd_revoke_record_s *);
static void flush_descriptor(journal_t *, struct journal_head *, int);
#endif

/* Utility functions to maintain the revoke table */

/* Borrowed from buffer.c: this is a tried and tested block hash function */
static inline int hash(journal_t *journal, unsigned long block)
{
        struct jbd_revoke_table_s *table = journal->j_revoke;
        int hash_shift = table->hash_shift;

        return ((block << (hash_shift - 6)) ^
                (block >> 13) ^
                (block << (hash_shift - 12))) & (table->hash_size - 1);
}

static int insert_revoke_hash(journal_t *journal, unsigned long blocknr,
                              tid_t seq)
{
        struct list_head *hash_list;
        struct jbd_revoke_record_s *record;

repeat:
        record = kmem_cache_alloc(revoke_record_cache, GFP_NOFS);
        if (!record)
                goto oom;

        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;

oom:
        if (!journal_oom_retry)
                return -ENOMEM;
        jbd_debug(1, "ENOMEM in %s, retrying\n", __func__);
        yield();
        goto repeat;
}

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

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

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

        spin_lock(&journal->j_revoke_lock);
        record = (struct jbd_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 jbd_revoke_record_s *) record->hash.next;
        }
        spin_unlock(&journal->j_revoke_lock);
        return NULL;
}

void journal_destroy_revoke_caches(void)
{
        if (revoke_record_cache) {
                kmem_cache_destroy(revoke_record_cache);
                revoke_record_cache = NULL;
        }
        if (revoke_table_cache) {
                kmem_cache_destroy(revoke_table_cache);
                revoke_table_cache = NULL;
        }
}

int __init journal_init_revoke_caches(void)
{
        J_ASSERT(!revoke_record_cache);
        J_ASSERT(!revoke_table_cache);

        revoke_record_cache = kmem_cache_create("revoke_record",
                                           sizeof(struct jbd_revoke_record_s),
                                           0,
                                           SLAB_HWCACHE_ALIGN|SLAB_TEMPORARY,
                                           NULL);
        if (!revoke_record_cache)
                goto record_cache_failure;

        revoke_table_cache = kmem_cache_create("revoke_table",
                                           sizeof(struct jbd_revoke_table_s),
                                           0, SLAB_TEMPORARY, NULL);
        if (!revoke_table_cache)
                goto table_cache_failure;

        return 0;

table_cache_failure:
        journal_destroy_revoke_caches();
record_cache_failure:
        return -ENOMEM;
}

static struct jbd_revoke_table_s *journal_init_revoke_table(int hash_size)
{
        int shift = 0;
        int tmp = hash_size;
        struct jbd_revoke_table_s *table;

        table = kmem_cache_alloc(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(hash_size * sizeof(struct list_head), GFP_KERNEL);
        if (!table->hash_table) {
                kmem_cache_free(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 journal_destroy_revoke_table(struct jbd_revoke_table_s *table)
{
        int i;
        struct list_head *hash_list;

        for (i = 0; i < table->hash_size; i++) {
                hash_list = &table->hash_table[i];
                J_ASSERT(list_empty(hash_list));
        }

        kfree(table->hash_table);
        kmem_cache_free(revoke_table_cache, table);
}

/* Initialise the revoke table for a given journal to a given size. */
int journal_init_revoke(journal_t *journal, int hash_size)
{
        J_ASSERT(journal->j_revoke_table[0] == NULL);
        J_ASSERT(is_power_of_2(hash_size));

        journal->j_revoke_table[0] = journal_init_revoke_table(hash_size);
        if (!journal->j_revoke_table[0])
                goto fail0;

        journal->j_revoke_table[1] = journal_init_revoke_table(hash_size);
        if (!journal->j_revoke_table[1])
                goto fail1;

        journal->j_revoke = journal->j_revoke_table[1];

        spin_lock_init(&journal->j_revoke_lock);

        return 0;

fail1:
        journal_destroy_revoke_table(journal->j_revoke_table[0]);
fail0:
        return -ENOMEM;
}

/* Destroy a journal's revoke table.  The table must already be empty! */
void journal_destroy_revoke(journal_t *journal)
{
        journal->j_revoke = NULL;
        if (journal->j_revoke_table[0])
                journal_destroy_revoke_table(journal->j_revoke_table[0]);
        if (journal->j_revoke_table[1])
                journal_destroy_revoke_table(journal->j_revoke_table[1]);
}


#ifdef __KERNEL__

/*
 * journal_revoke: revoke a given buffer_head from the journal.  This
 * prevents the block from being replayed during recovery if we take a
 * crash after this current transaction commits.  Any subsequent
 * metadata writes of the buffer in this transaction cancel the
 * revoke.
 *
 * Note that this call may block --- it is up to the caller to make
 * sure that there are no further calls to journal_write_metadata
 * before the revoke is complete.  In ext3, this implies calling the
 * revoke before clearing the block bitmap when we are deleting
 * metadata.
 *
 * Revoke performs a journal_forget on any buffer_head passed in as a
 * parameter, but does _not_ forget the buffer_head if the bh was only
 * found implicitly.
 *
 * bh_in may not be a journalled buffer - it may have come off
 * the hash tables without an attached journal_head.
 *
 * If bh_in is non-zero, journal_revoke() will decrement its b_count
 * by one.
 */

int journal_revoke(handle_t *handle, unsigned long blocknr,
                   struct buffer_head *bh_in)
{
        struct buffer_head *bh = NULL;
        journal_t *journal;
        struct block_device *bdev;
        int err;

        might_sleep();
        if (bh_in)
                BUFFER_TRACE(bh_in, "enter");

        journal = handle->h_transaction->t_journal;
        if (!journal_set_features(journal, 0, 0, JFS_FEATURE_INCOMPAT_REVOKE)){
                J_ASSERT (!"Cannot set revoke feature!");
                return -EINVAL;
        }

        bdev = journal->j_fs_dev;
        bh = bh_in;

        if (!bh) {
                bh = __find_get_block(bdev, blocknr, journal->j_blocksize);
                if (bh)
                        BUFFER_TRACE(bh, "found on hash");
        }
#ifdef JBD_EXPENSIVE_CHECKING
        else {
                struct buffer_head *bh2;

                /* If there is a different buffer_head lying around in
                 * memory anywhere... */
                bh2 = __find_get_block(bdev, blocknr, journal->j_blocksize);
                if (bh2) {
                        /* ... and it has RevokeValid status... */
                        if (bh2 != bh && buffer_revokevalid(bh2))
                                /* ...then it better be revoked too,
                                 * since it's illegal to create a revoke
                                 * record against a buffer_head which is
                                 * not marked revoked --- that would
                                 * risk missing a subsequent revoke
                                 * cancel. */
                                J_ASSERT_BH(bh2, buffer_revoked(bh2));
                        put_bh(bh2);
                }
        }
#endif

        /* We really ought not ever to revoke twice in a row without
           first having the revoke cancelled: it's illegal to free a
           block twice without allocating it in between! */
        if (bh) {
                if (!J_EXPECT_BH(bh, !buffer_revoked(bh),
                                 "inconsistent data on disk")) {
                        if (!bh_in)
                                brelse(bh);
                        return -EIO;
                }
                set_buffer_revoked(bh);
                set_buffer_revokevalid(bh);
                if (bh_in) {
                        BUFFER_TRACE(bh_in, "call journal_forget");
                        journal_forget(handle, bh_in);
                } else {
                        BUFFER_TRACE(bh, "call brelse");
                        __brelse(bh);
                }
        }

        jbd_debug(2, "insert revoke for block %lu, bh_in=%p\n", blocknr, bh_in);
        err = insert_revoke_hash(journal, blocknr,
                                handle->h_transaction->t_tid);
        BUFFER_TRACE(bh_in, "exit");
        return err;
}

/*
 * Cancel an outstanding revoke.  For use only internally by the
 * journaling code (called from journal_get_write_access).
 *
 * We trust buffer_revoked() on the buffer if the buffer is already
 * being journaled: if there is no revoke pending on the buffer, then we
 * don't do anything here.
 *
 * This would break if it were possible for a buffer to be revoked and
 * discarded, and then reallocated within the same transaction.  In such
 * a case we would have lost the revoked bit, but when we arrived here
 * the second time we would still have a pending revoke to cancel.  So,
 * do not trust the Revoked bit on buffers unless RevokeValid is also
 * set.
 */
int journal_cancel_revoke(handle_t *handle, struct journal_head *jh)
{
        struct jbd_revoke_record_s *record;
        journal_t *journal = handle->h_transaction->t_journal;
        int need_cancel;
        int did_revoke = 0;     /* akpm: debug */
        struct buffer_head *bh = jh2bh(jh);

        jbd_debug(4, "journal_head %p, cancelling revoke\n", jh);

        /* Is the existing Revoke bit valid?  If so, we trust it, and
         * only perform the full cancel if the revoke bit is set.  If
         * not, we can't trust the revoke bit, and we need to do the
         * full search for a revoke record. */
        if (test_set_buffer_revokevalid(bh)) {
                need_cancel = test_clear_buffer_revoked(bh);
        } else {
                need_cancel = 1;
                clear_buffer_revoked(bh);
        }

        if (need_cancel) {
                record = find_revoke_record(journal, bh->b_blocknr);
                if (record) {
                        jbd_debug(4, "cancelled existing revoke on "
                                  "blocknr %llu\n", (unsigned long long)bh->b_blocknr);
                        spin_lock(&journal->j_revoke_lock);
                        list_del(&record->hash);
                        spin_unlock(&journal->j_revoke_lock);
                        kmem_cache_free(revoke_record_cache, record);
                        did_revoke = 1;
                }
        }

#ifdef JBD_EXPENSIVE_CHECKING
        /* There better not be one left behind by now! */
        record = find_revoke_record(journal, bh->b_blocknr);
        J_ASSERT_JH(jh, record == NULL);
#endif

        /* Finally, have we just cleared revoke on an unhashed
         * buffer_head?  If so, we'd better make sure we clear the
         * revoked status on any hashed alias too, otherwise the revoke
         * state machine will get very upset later on. */
        if (need_cancel) {
                struct buffer_head *bh2;
                bh2 = __find_get_block(bh->b_bdev, bh->b_blocknr, bh->b_size);
                if (bh2) {
                        if (bh2 != bh)
                                clear_buffer_revoked(bh2);
                        __brelse(bh2);
                }
        }
        return did_revoke;
}

/* journal_switch_revoke table select j_revoke for next transaction
 * we do not want to suspend any processing until all revokes are
 * written -bzzz
 */
void journal_switch_revoke_table(journal_t *journal)
{
        int i;

        if (journal->j_revoke == journal->j_revoke_table[0])
                journal->j_revoke = journal->j_revoke_table[1];
        else
                journal->j_revoke = journal->j_revoke_table[0];

        for (i = 0; i < journal->j_revoke->hash_size; i++)
                INIT_LIST_HEAD(&journal->j_revoke->hash_table[i]);
}

/*
 * Write revoke records to the journal for all entries in the current
 * revoke hash, deleting the entries as we go.
 */
void journal_write_revoke_records(journal_t *journal,
                                  transaction_t *transaction)
{
        struct journal_head *descriptor;
        struct jbd_revoke_record_s *record;
        struct jbd_revoke_table_s *revoke;
        struct list_head *hash_list;
        int i, offset, count;

        descriptor = NULL;
        offset = 0;
        count = 0;

        /* select revoke table for committing transaction */
        revoke = journal->j_revoke == journal->j_revoke_table[0] ?
                journal->j_revoke_table[1] : journal->j_revoke_table[0];

        for (i = 0; i < revoke->hash_size; i++) {
                hash_list = &revoke->hash_table[i];

                while (!list_empty(hash_list)) {
                        record = (struct jbd_revoke_record_s *)
                                hash_list->next;
                        write_one_revoke_record(journal, transaction,
                                                &descriptor, &offset,
                                                record);
                        count++;
                        list_del(&record->hash);
                        kmem_cache_free(revoke_record_cache, record);
                }
        }
        if (descriptor)
                flush_descriptor(journal, descriptor, offset);
        jbd_debug(1, "Wrote %d revoke records\n", count);
}

/*
 * Write out one revoke record.  We need to create a new descriptor
 * block if the old one is full or if we have not already created one.
 */

static void write_one_revoke_record(journal_t *journal,
                                    transaction_t *transaction,
                                    struct journal_head **descriptorp,
                                    int *offsetp,
                                    struct jbd_revoke_record_s *record)
{
        struct journal_head *descriptor;
        int offset;
        journal_header_t *header;

        /* If we are already aborting, this all becomes a noop.  We
           still need to go round the loop in
           journal_write_revoke_records in order to free all of the
           revoke records: only the IO to the journal is omitted. */
        if (is_journal_aborted(journal))
                return;

        descriptor = *descriptorp;
        offset = *offsetp;

        /* Make sure we have a descriptor with space left for the record */
        if (descriptor) {
                if (offset == journal->j_blocksize) {
                        flush_descriptor(journal, descriptor, offset);
                        descriptor = NULL;
                }
        }

        if (!descriptor) {
                descriptor = journal_get_descriptor_buffer(journal);
                if (!descriptor)
                        return;
                header = (journal_header_t *) &jh2bh(descriptor)->b_data[0];
                header->h_magic     = cpu_to_be32(JFS_MAGIC_NUMBER);
                header->h_blocktype = cpu_to_be32(JFS_REVOKE_BLOCK);
                header->h_sequence  = cpu_to_be32(transaction->t_tid);

                /* Record it so that we can wait for IO completion later */
                JBUFFER_TRACE(descriptor, "file as BJ_LogCtl");
                journal_file_buffer(descriptor, transaction, BJ_LogCtl);

                offset = sizeof(journal_revoke_header_t);
                *descriptorp = descriptor;
        }

        * ((__be32 *)(&jh2bh(descriptor)->b_data[offset])) =
                cpu_to_be32(record->blocknr);
        offset += 4;
        *offsetp = offset;
}

/*
 * Flush a revoke descriptor out to the journal.  If we are aborting,
 * this is a noop; otherwise we are generating a buffer which needs to
 * be waited for during commit, so it has to go onto the appropriate
 * journal buffer list.
 */

static void flush_descriptor(journal_t *journal,
                             struct journal_head *descriptor,
                             int offset)
{
        journal_revoke_header_t *header;
        struct buffer_head *bh = jh2bh(descriptor);

        if (is_journal_aborted(journal)) {
                put_bh(bh);
                return;
        }

        header = (journal_revoke_header_t *) jh2bh(descriptor)->b_data;
        header->r_count = cpu_to_be32(offset);
        set_buffer_jwrite(bh);
        BUFFER_TRACE(bh, "write");
        set_buffer_dirty(bh);
        ll_rw_block(SWRITE, 1, &bh);
}
#endif

/*
 * Revoke support for recovery.
 *
 * Recovery needs to be able to:
 *
 *  record all revoke records, including the tid of the latest instance
 *  of each revoke in the journal
 *
 *  check whether a given block in a given transaction should be replayed
 *  (ie. has not been revoked by a revoke record in that or a subsequent
 *  transaction)
 *
 *  empty the revoke table after recovery.
 */

/*
 * First, setting revoke records.  We create a new revoke record for
 * every block ever revoked in the log as we scan it for recovery, and
 * we update the existing records if we find multiple revokes for a
 * single block.
 */

int journal_set_revoke(journal_t *journal,
                       unsigned long blocknr,
                       tid_t sequence)
{
        struct jbd_revoke_record_s *record;

        record = find_revoke_record(journal, blocknr);
        if (record) {
                /* If we have multiple occurrences, only record the
                 * latest sequence number in the hashed record */
                if (tid_gt(sequence, record->sequence))
                        record->sequence = sequence;
                return 0;
        }
        return insert_revoke_hash(journal, blocknr, sequence);
}

/*
 * Test revoke records.  For a given block referenced in the log, has
 * that block been revoked?  A revoke record with a given transaction
 * sequence number revokes all blocks in that transaction and earlier
 * ones, but later transactions still need replayed.
 */

int journal_test_revoke(journal_t *journal,
                        unsigned long blocknr,
                        tid_t sequence)
{
        struct jbd_revoke_record_s *record;

        record = find_revoke_record(journal, blocknr);
        if (!record)
                return 0;
        if (tid_gt(sequence, record->sequence))
                return 0;
        return 1;
}

/*
 * Finally, once recovery is over, we need to clear the revoke table so
 * that it can be reused by the running filesystem.
 */

void journal_clear_revoke(journal_t *journal)
{
        int i;
        struct list_head *hash_list;
        struct jbd_revoke_record_s *record;
        struct jbd_revoke_table_s *revoke;

        revoke = journal->j_revoke;

        for (i = 0; i < revoke->hash_size; i++) {
                hash_list = &revoke->hash_table[i];
                while (!list_empty(hash_list)) {
                        record = (struct jbd_revoke_record_s*) hash_list->next;
                        list_del(&record->hash);
                        kmem_cache_free(revoke_record_cache, record);
                }
        }
}