jbd2: remove always true condition in __journal_try_to_free_buffer()

[mirror_ubuntu-artful-kernel.git] / fs / jbd2 / checkpoint.c

/*
 * linux/fs/jbd2/checkpoint.c
 *
 * Written by Stephen C. Tweedie <sct@redhat.com>, 1999
 *
 * Copyright 1999 Red Hat Software --- 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.
 *
 * Checkpoint routines for the generic filesystem journaling code.
 * Part of the ext2fs journaling system.
 *
 * Checkpointing is the process of ensuring that a section of the log is
 * committed fully to disk, so that that portion of the log can be
 * reused.
 */

#include <linux/time.h>
#include <linux/fs.h>
#include <linux/jbd2.h>
#include <linux/errno.h>
#include <linux/slab.h>
#include <linux/blkdev.h>
#include <trace/events/jbd2.h>

/*
 * Unlink a buffer from a transaction checkpoint list.
 *
 * Called with j_list_lock held.
 */
static inline void __buffer_unlink_first(struct journal_head *jh)
{
        transaction_t *transaction = jh->b_cp_transaction;

        jh->b_cpnext->b_cpprev = jh->b_cpprev;
        jh->b_cpprev->b_cpnext = jh->b_cpnext;
        if (transaction->t_checkpoint_list == jh) {
                transaction->t_checkpoint_list = jh->b_cpnext;
                if (transaction->t_checkpoint_list == jh)
                        transaction->t_checkpoint_list = NULL;
        }
}

/*
 * Unlink a buffer from a transaction checkpoint(io) list.
 *
 * Called with j_list_lock held.
 */
static inline void __buffer_unlink(struct journal_head *jh)
{
        transaction_t *transaction = jh->b_cp_transaction;

        __buffer_unlink_first(jh);
        if (transaction->t_checkpoint_io_list == jh) {
                transaction->t_checkpoint_io_list = jh->b_cpnext;
                if (transaction->t_checkpoint_io_list == jh)
                        transaction->t_checkpoint_io_list = NULL;
        }
}

/*
 * Move a buffer from the checkpoint list to the checkpoint io list
 *
 * Called with j_list_lock held
 */
static inline void __buffer_relink_io(struct journal_head *jh)
{
        transaction_t *transaction = jh->b_cp_transaction;

        __buffer_unlink_first(jh);

        if (!transaction->t_checkpoint_io_list) {
                jh->b_cpnext = jh->b_cpprev = jh;
        } else {
                jh->b_cpnext = transaction->t_checkpoint_io_list;
                jh->b_cpprev = transaction->t_checkpoint_io_list->b_cpprev;
                jh->b_cpprev->b_cpnext = jh;
                jh->b_cpnext->b_cpprev = jh;
        }
        transaction->t_checkpoint_io_list = jh;
}

/*
 * Try to release a checkpointed buffer from its transaction.
 * Returns 1 if we released it and 2 if we also released the
 * whole transaction.
 *
 * Requires j_list_lock
 * Called under jbd_lock_bh_state(jh2bh(jh)), and drops it
 */
static int __try_to_free_cp_buf(struct journal_head *jh)
{
        int ret = 0;
        struct buffer_head *bh = jh2bh(jh);

        if (jh->b_jlist == BJ_None && !buffer_locked(bh) &&
            !buffer_dirty(bh) && !buffer_write_io_error(bh)) {
                /*
                 * Get our reference so that bh cannot be freed before
                 * we unlock it
                 */
                get_bh(bh);
                JBUFFER_TRACE(jh, "remove from checkpoint list");
                ret = __jbd2_journal_remove_checkpoint(jh) + 1;
                jbd_unlock_bh_state(bh);
                BUFFER_TRACE(bh, "release");
                __brelse(bh);
        } else {
                jbd_unlock_bh_state(bh);
        }
        return ret;
}

/*
 * __jbd2_log_wait_for_space: wait until there is space in the journal.
 *
 * Called under j-state_lock *only*.  It will be unlocked if we have to wait
 * for a checkpoint to free up some space in the log.
 */
void __jbd2_log_wait_for_space(journal_t *journal)
{
        int nblocks, space_left;
        /* assert_spin_locked(&journal->j_state_lock); */

        nblocks = jbd_space_needed(journal);
        while (__jbd2_log_space_left(journal) < nblocks) {
                if (journal->j_flags & JBD2_ABORT)
                        return;
                write_unlock(&journal->j_state_lock);
                mutex_lock(&journal->j_checkpoint_mutex);

                /*
                 * Test again, another process may have checkpointed while we
                 * were waiting for the checkpoint lock. If there are no
                 * transactions ready to be checkpointed, try to recover
                 * journal space by calling cleanup_journal_tail(), and if
                 * that doesn't work, by waiting for the currently committing
                 * transaction to complete.  If there is absolutely no way
                 * to make progress, this is either a BUG or corrupted
                 * filesystem, so abort the journal and leave a stack
                 * trace for forensic evidence.
                 */
                write_lock(&journal->j_state_lock);
                spin_lock(&journal->j_list_lock);
                nblocks = jbd_space_needed(journal);
                space_left = __jbd2_log_space_left(journal);
                if (space_left < nblocks) {
                        int chkpt = journal->j_checkpoint_transactions != NULL;
                        tid_t tid = 0;

                        if (journal->j_committing_transaction)
                                tid = journal->j_committing_transaction->t_tid;
                        spin_unlock(&journal->j_list_lock);
                        write_unlock(&journal->j_state_lock);
                        if (chkpt) {
                                jbd2_log_do_checkpoint(journal);
                        } else if (jbd2_cleanup_journal_tail(journal) == 0) {
                                /* We were able to recover space; yay! */
                                ;
                        } else if (tid) {
                                jbd2_log_wait_commit(journal, tid);
                        } else {
                                printk(KERN_ERR "%s: needed %d blocks and "
                                       "only had %d space available\n",
                                       __func__, nblocks, space_left);
                                printk(KERN_ERR "%s: no way to get more "
                                       "journal space in %s\n", __func__,
                                       journal->j_devname);
                                WARN_ON(1);
                                jbd2_journal_abort(journal, 0);
                        }
                        write_lock(&journal->j_state_lock);
                } else {
                        spin_unlock(&journal->j_list_lock);
                }
                mutex_unlock(&journal->j_checkpoint_mutex);
        }
}

/*
 * We were unable to perform jbd_trylock_bh_state() inside j_list_lock.
 * The caller must restart a list walk.  Wait for someone else to run
 * jbd_unlock_bh_state().
 */
static void jbd_sync_bh(journal_t *journal, struct buffer_head *bh)
        __releases(journal->j_list_lock)
{
        get_bh(bh);
        spin_unlock(&journal->j_list_lock);
        jbd_lock_bh_state(bh);
        jbd_unlock_bh_state(bh);
        put_bh(bh);
}

/*
 * Clean up transaction's list of buffers submitted for io.
 * We wait for any pending IO to complete and remove any clean
 * buffers. Note that we take the buffers in the opposite ordering
 * from the one in which they were submitted for IO.
 *
 * Return 0 on success, and return <0 if some buffers have failed
 * to be written out.
 *
 * Called with j_list_lock held.
 */
static int __wait_cp_io(journal_t *journal, transaction_t *transaction)
{
        struct journal_head *jh;
        struct buffer_head *bh;
        tid_t this_tid;
        int released = 0;
        int ret = 0;

        this_tid = transaction->t_tid;
restart:
        /* Did somebody clean up the transaction in the meanwhile? */
        if (journal->j_checkpoint_transactions != transaction ||
                        transaction->t_tid != this_tid)
                return ret;
        while (!released && transaction->t_checkpoint_io_list) {
                jh = transaction->t_checkpoint_io_list;
                bh = jh2bh(jh);
                if (!jbd_trylock_bh_state(bh)) {
                        jbd_sync_bh(journal, bh);
                        spin_lock(&journal->j_list_lock);
                        goto restart;
                }
                get_bh(bh);
                if (buffer_locked(bh)) {
                        spin_unlock(&journal->j_list_lock);
                        jbd_unlock_bh_state(bh);
                        wait_on_buffer(bh);
                        /* the journal_head may have gone by now */
                        BUFFER_TRACE(bh, "brelse");
                        __brelse(bh);
                        spin_lock(&journal->j_list_lock);
                        goto restart;
                }
                if (unlikely(buffer_write_io_error(bh)))
                        ret = -EIO;

                /*
                 * Now in whatever state the buffer currently is, we know that
                 * it has been written out and so we can drop it from the list
                 */
                released = __jbd2_journal_remove_checkpoint(jh);
                jbd_unlock_bh_state(bh);
                __brelse(bh);
        }

        return ret;
}

static void
__flush_batch(journal_t *journal, int *batch_count)
{
        int i;
        struct blk_plug plug;

        blk_start_plug(&plug);
        for (i = 0; i < *batch_count; i++)
                write_dirty_buffer(journal->j_chkpt_bhs[i], WRITE_SYNC);
        blk_finish_plug(&plug);

        for (i = 0; i < *batch_count; i++) {
                struct buffer_head *bh = journal->j_chkpt_bhs[i];
                BUFFER_TRACE(bh, "brelse");
                __brelse(bh);
        }
        *batch_count = 0;
}

/*
 * Try to flush one buffer from the checkpoint list to disk.
 *
 * Return 1 if something happened which requires us to abort the current
 * scan of the checkpoint list.  Return <0 if the buffer has failed to
 * be written out.
 *
 * Called with j_list_lock held and drops it if 1 is returned
 * Called under jbd_lock_bh_state(jh2bh(jh)), and drops it
 */
static int __process_buffer(journal_t *journal, struct journal_head *jh,
                            int *batch_count, transaction_t *transaction)
{
        struct buffer_head *bh = jh2bh(jh);
        int ret = 0;

        if (buffer_locked(bh)) {
                get_bh(bh);
                spin_unlock(&journal->j_list_lock);
                jbd_unlock_bh_state(bh);
                wait_on_buffer(bh);
                /* the journal_head may have gone by now */
                BUFFER_TRACE(bh, "brelse");
                __brelse(bh);
                ret = 1;
        } else if (jh->b_transaction != NULL) {
                transaction_t *t = jh->b_transaction;
                tid_t tid = t->t_tid;

                transaction->t_chp_stats.cs_forced_to_close++;
                spin_unlock(&journal->j_list_lock);
                jbd_unlock_bh_state(bh);
                if (unlikely(journal->j_flags & JBD2_UNMOUNT))
                        /*
                         * The journal thread is dead; so starting and
                         * waiting for a commit to finish will cause
                         * us to wait for a _very_ long time.
                         */
                        printk(KERN_ERR "JBD2: %s: "
                               "Waiting for Godot: block %llu\n",
                               journal->j_devname,
                               (unsigned long long) bh->b_blocknr);
                jbd2_log_start_commit(journal, tid);
                jbd2_log_wait_commit(journal, tid);
                ret = 1;
        } else if (!buffer_dirty(bh)) {
                ret = 1;
                if (unlikely(buffer_write_io_error(bh)))
                        ret = -EIO;
                get_bh(bh);
                J_ASSERT_JH(jh, !buffer_jbddirty(bh));
                BUFFER_TRACE(bh, "remove from checkpoint");
                __jbd2_journal_remove_checkpoint(jh);
                spin_unlock(&journal->j_list_lock);
                jbd_unlock_bh_state(bh);
                __brelse(bh);
        } else {
                /*
                 * Important: we are about to write the buffer, and
                 * possibly block, while still holding the journal lock.
                 * We cannot afford to let the transaction logic start
                 * messing around with this buffer before we write it to
                 * disk, as that would break recoverability.
                 */
                BUFFER_TRACE(bh, "queue");
                get_bh(bh);
                J_ASSERT_BH(bh, !buffer_jwrite(bh));
                journal->j_chkpt_bhs[*batch_count] = bh;
                __buffer_relink_io(jh);
                jbd_unlock_bh_state(bh);
                transaction->t_chp_stats.cs_written++;
                (*batch_count)++;
                if (*batch_count == JBD2_NR_BATCH) {
                        spin_unlock(&journal->j_list_lock);
                        __flush_batch(journal, batch_count);
                        ret = 1;
                }
        }
        return ret;
}

/*
 * Perform an actual checkpoint. We take the first transaction on the
 * list of transactions to be checkpointed and send all its buffers
 * to disk. We submit larger chunks of data at once.
 *
 * The journal should be locked before calling this function.
 * Called with j_checkpoint_mutex held.
 */
int jbd2_log_do_checkpoint(journal_t *journal)
{
        transaction_t *transaction;
        tid_t this_tid;
        int result;

        jbd_debug(1, "Start checkpoint\n");

        /*
         * First thing: if there are any transactions in the log which
         * don't need checkpointing, just eliminate them from the
         * journal straight away.
         */
        result = jbd2_cleanup_journal_tail(journal);
        trace_jbd2_checkpoint(journal, result);
        jbd_debug(1, "cleanup_journal_tail returned %d\n", result);
        if (result <= 0)
                return result;

        /*
         * OK, we need to start writing disk blocks.  Take one transaction
         * and write it.
         */
        result = 0;
        spin_lock(&journal->j_list_lock);
        if (!journal->j_checkpoint_transactions)
                goto out;
        transaction = journal->j_checkpoint_transactions;
        if (transaction->t_chp_stats.cs_chp_time == 0)
                transaction->t_chp_stats.cs_chp_time = jiffies;
        this_tid = transaction->t_tid;
restart:
        /*
         * If someone cleaned up this transaction while we slept, we're
         * done (maybe it's a new transaction, but it fell at the same
         * address).
         */
        if (journal->j_checkpoint_transactions == transaction &&
                        transaction->t_tid == this_tid) {
                int batch_count = 0;
                struct journal_head *jh;
                int retry = 0, err;

                while (!retry && transaction->t_checkpoint_list) {
                        struct buffer_head *bh;

                        jh = transaction->t_checkpoint_list;
                        bh = jh2bh(jh);
                        if (!jbd_trylock_bh_state(bh)) {
                                jbd_sync_bh(journal, bh);
                                retry = 1;
                                break;
                        }
                        retry = __process_buffer(journal, jh, &batch_count,
                                                 transaction);
                        if (retry < 0 && !result)
                                result = retry;
                        if (!retry && (need_resched() ||
                                spin_needbreak(&journal->j_list_lock))) {
                                spin_unlock(&journal->j_list_lock);
                                retry = 1;
                                break;
                        }
                }

                if (batch_count) {
                        if (!retry) {
                                spin_unlock(&journal->j_list_lock);
                                retry = 1;
                        }
                        __flush_batch(journal, &batch_count);
                }

                if (retry) {
                        spin_lock(&journal->j_list_lock);
                        goto restart;
                }
                /*
                 * Now we have cleaned up the first transaction's checkpoint
                 * list. Let's clean up the second one
                 */
                err = __wait_cp_io(journal, transaction);
                if (!result)
                        result = err;
        }
out:
        spin_unlock(&journal->j_list_lock);
        if (result < 0)
                jbd2_journal_abort(journal, result);
        else
                result = jbd2_cleanup_journal_tail(journal);

        return (result < 0) ? result : 0;
}

/*
 * Check the list of checkpoint transactions for the journal to see if
 * we have already got rid of any since the last update of the log tail
 * in the journal superblock.  If so, we can instantly roll the
 * superblock forward to remove those transactions from the log.
 *
 * Return <0 on error, 0 on success, 1 if there was nothing to clean up.
 *
 * Called with the journal lock held.
 *
 * This is the only part of the journaling code which really needs to be
 * aware of transaction aborts.  Checkpointing involves writing to the
 * main filesystem area rather than to the journal, so it can proceed
 * even in abort state, but we must not update the super block if
 * checkpointing may have failed.  Otherwise, we would lose some metadata
 * buffers which should be written-back to the filesystem.
 */

int jbd2_cleanup_journal_tail(journal_t *journal)
{
        tid_t           first_tid;
        unsigned long   blocknr;

        if (is_journal_aborted(journal))
                return 1;

        if (!jbd2_journal_get_log_tail(journal, &first_tid, &blocknr))
                return 1;
        J_ASSERT(blocknr != 0);

        /*
         * We need to make sure that any blocks that were recently written out
         * --- perhaps by jbd2_log_do_checkpoint() --- are flushed out before
         * we drop the transactions from the journal. It's unlikely this will
         * be necessary, especially with an appropriately sized journal, but we
         * need this to guarantee correctness.  Fortunately
         * jbd2_cleanup_journal_tail() doesn't get called all that often.
         */
        if (journal->j_flags & JBD2_BARRIER)
                blkdev_issue_flush(journal->j_fs_dev, GFP_KERNEL, NULL);

        __jbd2_update_log_tail(journal, first_tid, blocknr);
        return 0;
}


/* Checkpoint list management */

/*
 * journal_clean_one_cp_list
 *
 * Find all the written-back checkpoint buffers in the given list and
 * release them.
 *
 * Called with the journal locked.
 * Called with j_list_lock held.
 * Returns number of buffers reaped (for debug)
 */

static int journal_clean_one_cp_list(struct journal_head *jh, int *released)
{
        struct journal_head *last_jh;
        struct journal_head *next_jh = jh;
        int ret, freed = 0;

        *released = 0;
        if (!jh)
                return 0;

        last_jh = jh->b_cpprev;
        do {
                jh = next_jh;
                next_jh = jh->b_cpnext;
                /* Use trylock because of the ranking */
                if (jbd_trylock_bh_state(jh2bh(jh))) {
                        ret = __try_to_free_cp_buf(jh);
                        if (ret) {
                                freed++;
                                if (ret == 2) {
                                        *released = 1;
                                        return freed;
                                }
                        }
                }
                /*
                 * This function only frees up some memory
                 * if possible so we dont have an obligation
                 * to finish processing. Bail out if preemption
                 * requested:
                 */
                if (need_resched())
                        return freed;
        } while (jh != last_jh);

        return freed;
}

/*
 * journal_clean_checkpoint_list
 *
 * Find all the written-back checkpoint buffers in the journal and release them.
 *
 * Called with the journal locked.
 * Called with j_list_lock held.
 * Returns number of buffers reaped (for debug)
 */

int __jbd2_journal_clean_checkpoint_list(journal_t *journal)
{
        transaction_t *transaction, *last_transaction, *next_transaction;
        int ret = 0;
        int released;

        transaction = journal->j_checkpoint_transactions;
        if (!transaction)
                goto out;

        last_transaction = transaction->t_cpprev;
        next_transaction = transaction;
        do {
                transaction = next_transaction;
                next_transaction = transaction->t_cpnext;
                ret += journal_clean_one_cp_list(transaction->
                                t_checkpoint_list, &released);
                /*
                 * This function only frees up some memory if possible so we
                 * dont have an obligation to finish processing. Bail out if
                 * preemption requested:
                 */
                if (need_resched())
                        goto out;
                if (released)
                        continue;
                /*
                 * It is essential that we are as careful as in the case of
                 * t_checkpoint_list with removing the buffer from the list as
                 * we can possibly see not yet submitted buffers on io_list
                 */
                ret += journal_clean_one_cp_list(transaction->
                                t_checkpoint_io_list, &released);
                if (need_resched())
                        goto out;
        } while (transaction != last_transaction);
out:
        return ret;
}

/*
 * journal_remove_checkpoint: called after a buffer has been committed
 * to disk (either by being write-back flushed to disk, or being
 * committed to the log).
 *
 * We cannot safely clean a transaction out of the log until all of the
 * buffer updates committed in that transaction have safely been stored
 * elsewhere on disk.  To achieve this, all of the buffers in a
 * transaction need to be maintained on the transaction's checkpoint
 * lists until they have been rewritten, at which point this function is
 * called to remove the buffer from the existing transaction's
 * checkpoint lists.
 *
 * The function returns 1 if it frees the transaction, 0 otherwise.
 * The function can free jh and bh.
 *
 * This function is called with j_list_lock held.
 * This function is called with jbd_lock_bh_state(jh2bh(jh))
 */

int __jbd2_journal_remove_checkpoint(struct journal_head *jh)
{
        struct transaction_chp_stats_s *stats;
        transaction_t *transaction;
        journal_t *journal;
        int ret = 0;

        JBUFFER_TRACE(jh, "entry");

        if ((transaction = jh->b_cp_transaction) == NULL) {
                JBUFFER_TRACE(jh, "not on transaction");
                goto out;
        }
        journal = transaction->t_journal;

        JBUFFER_TRACE(jh, "removing from transaction");
        __buffer_unlink(jh);
        jh->b_cp_transaction = NULL;
        jbd2_journal_put_journal_head(jh);

        if (transaction->t_checkpoint_list != NULL ||
            transaction->t_checkpoint_io_list != NULL)
                goto out;

        /*
         * There is one special case to worry about: if we have just pulled the
         * buffer off a running or committing transaction's checkpoing list,
         * then even if the checkpoint list is empty, the transaction obviously
         * cannot be dropped!
         *
         * The locking here around t_state is a bit sleazy.
         * See the comment at the end of jbd2_journal_commit_transaction().
         */
        if (transaction->t_state != T_FINISHED)
                goto out;

        /* OK, that was the last buffer for the transaction: we can now
           safely remove this transaction from the log */
        stats = &transaction->t_chp_stats;
        if (stats->cs_chp_time)
                stats->cs_chp_time = jbd2_time_diff(stats->cs_chp_time,
                                                    jiffies);
        trace_jbd2_checkpoint_stats(journal->j_fs_dev->bd_dev,
                                    transaction->t_tid, stats);

        __jbd2_journal_drop_transaction(journal, transaction);
        jbd2_journal_free_transaction(transaction);

        /* Just in case anybody was waiting for more transactions to be
           checkpointed... */
        wake_up(&journal->j_wait_logspace);
        ret = 1;
out:
        return ret;
}

/*
 * journal_insert_checkpoint: put a committed buffer onto a checkpoint
 * list so that we know when it is safe to clean the transaction out of
 * the log.
 *
 * Called with the journal locked.
 * Called with j_list_lock held.
 */
void __jbd2_journal_insert_checkpoint(struct journal_head *jh,
                               transaction_t *transaction)
{
        JBUFFER_TRACE(jh, "entry");
        J_ASSERT_JH(jh, buffer_dirty(jh2bh(jh)) || buffer_jbddirty(jh2bh(jh)));
        J_ASSERT_JH(jh, jh->b_cp_transaction == NULL);

        /* Get reference for checkpointing transaction */
        jbd2_journal_grab_journal_head(jh2bh(jh));
        jh->b_cp_transaction = transaction;

        if (!transaction->t_checkpoint_list) {
                jh->b_cpnext = jh->b_cpprev = jh;
        } else {
                jh->b_cpnext = transaction->t_checkpoint_list;
                jh->b_cpprev = transaction->t_checkpoint_list->b_cpprev;
                jh->b_cpprev->b_cpnext = jh;
                jh->b_cpnext->b_cpprev = jh;
        }
        transaction->t_checkpoint_list = jh;
}

/*
 * We've finished with this transaction structure: adios...
 *
 * The transaction must have no links except for the checkpoint by this
 * point.
 *
 * Called with the journal locked.
 * Called with j_list_lock held.
 */

void __jbd2_journal_drop_transaction(journal_t *journal, transaction_t *transaction)
{
        assert_spin_locked(&journal->j_list_lock);
        if (transaction->t_cpnext) {
                transaction->t_cpnext->t_cpprev = transaction->t_cpprev;
                transaction->t_cpprev->t_cpnext = transaction->t_cpnext;
                if (journal->j_checkpoint_transactions == transaction)
                        journal->j_checkpoint_transactions =
                                transaction->t_cpnext;
                if (journal->j_checkpoint_transactions == transaction)
                        journal->j_checkpoint_transactions = NULL;
        }

        J_ASSERT(transaction->t_state == T_FINISHED);
        J_ASSERT(transaction->t_buffers == NULL);
        J_ASSERT(transaction->t_forget == NULL);
        J_ASSERT(transaction->t_iobuf_list == NULL);
        J_ASSERT(transaction->t_shadow_list == NULL);
        J_ASSERT(transaction->t_log_list == NULL);
        J_ASSERT(transaction->t_checkpoint_list == NULL);
        J_ASSERT(transaction->t_checkpoint_io_list == NULL);
        J_ASSERT(atomic_read(&transaction->t_updates) == 0);
        J_ASSERT(journal->j_committing_transaction != transaction);
        J_ASSERT(journal->j_running_transaction != transaction);

        trace_jbd2_drop_transaction(journal, transaction);

        jbd_debug(1, "Dropping transaction %d, all done\n", transaction->t_tid);
}