forking JBD2

diff -puN /dev/null fs/jbd2/checkpoint.c
@@ -0,0 +1,696 @@
+/*
+ * linux/fs/checkpoint.c
+ *
+ * Written by Stephen C. Tweedie <[email protected]>, 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>
+
+/*
+ * 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)) {
+		JBUFFER_TRACE(jh, "remove from checkpoint list");
+		ret = __journal_remove_checkpoint(jh) + 1;
+		jbd_unlock_bh_state(bh);
+		journal_remove_journal_head(bh);
+		BUFFER_TRACE(bh, "release");
+		__brelse(bh);
+	} else {
+		jbd_unlock_bh_state(bh);
+	}
+	return ret;
+}
+
+/*
+ * __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 __log_wait_for_space(journal_t *journal)
+{
+	int nblocks;
+	assert_spin_locked(&journal->j_state_lock);
+
+	nblocks = jbd_space_needed(journal);
+	while (__log_space_left(journal) < nblocks) {
+		if (journal->j_flags & JFS_ABORT)
+			return;
+		spin_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
+		 */
+		spin_lock(&journal->j_state_lock);
+		nblocks = jbd_space_needed(journal);
+		if (__log_space_left(journal) < nblocks) {
+			spin_unlock(&journal->j_state_lock);
+			log_do_checkpoint(journal);
+			spin_lock(&journal->j_state_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)
+{
+	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.
+ *
+ * Called with j_list_lock held.
+ */
+static void __wait_cp_io(journal_t *journal, transaction_t *transaction)
+{
+	struct journal_head *jh;
+	struct buffer_head *bh;
+	tid_t this_tid;
+	int released = 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;
+	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;
+		}
+		if (buffer_locked(bh)) {
+			atomic_inc(&bh->b_count);
+			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;
+		}
+		/*
+		 * 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 = __journal_remove_checkpoint(jh);
+		jbd_unlock_bh_state(bh);
+		journal_remove_journal_head(bh);
+		__brelse(bh);
+	}
+}
+
+#define NR_BATCH	64
+
+static void
+__flush_batch(journal_t *journal, struct buffer_head **bhs, int *batch_count)
+{
+	int i;
+
+	ll_rw_block(SWRITE, *batch_count, bhs);
+	for (i = 0; i < *batch_count; i++) {
+		struct buffer_head *bh = bhs[i];
+		clear_buffer_jwrite(bh);
+		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.
+ *
+ * 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,
+			struct buffer_head **bhs, int *batch_count)
+{
+	struct buffer_head *bh = jh2bh(jh);
+	int ret = 0;
+
+	if (buffer_locked(bh)) {
+		atomic_inc(&bh->b_count);
+		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;
+
+		spin_unlock(&journal->j_list_lock);
+		jbd_unlock_bh_state(bh);
+		log_start_commit(journal, tid);
+		jbd2_log_wait_commit(journal, tid);
+		ret = 1;
+	} else if (!buffer_dirty(bh)) {
+		J_ASSERT_JH(jh, !buffer_jbddirty(bh));
+		BUFFER_TRACE(bh, "remove from checkpoint");
+		__journal_remove_checkpoint(jh);
+		spin_unlock(&journal->j_list_lock);
+		jbd_unlock_bh_state(bh);
+		journal_remove_journal_head(bh);
+		__brelse(bh);
+		ret = 1;
+	} 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));
+		set_buffer_jwrite(bh);
+		bhs[*batch_count] = bh;
+		__buffer_relink_io(jh);
+		jbd_unlock_bh_state(bh);
+		(*batch_count)++;
+		if (*batch_count == NR_BATCH) {
+			spin_unlock(&journal->j_list_lock);
+			__flush_batch(journal, bhs, 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.
+ */
+int 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 = cleanup_journal_tail(journal);
+	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.
+	 */
+	spin_lock(&journal->j_list_lock);
+	if (!journal->j_checkpoint_transactions)
+		goto out;
+	transaction = journal->j_checkpoint_transactions;
+	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 buffer_head *bhs[NR_BATCH];
+		struct journal_head *jh;
+		int retry = 0;
+
+		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, bhs,&batch_count);
+			if (!retry && lock_need_resched(&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, bhs, &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
+		 */
+		__wait_cp_io(journal, transaction);
+	}
+out:
+	spin_unlock(&journal->j_list_lock);
+	result = cleanup_journal_tail(journal);
+	if (result < 0)
+		return result;
+	return 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 journal superblock if
+ * we have an abort error outstanding.
+ */
+
+int cleanup_journal_tail(journal_t *journal)
+{
+	transaction_t * transaction;
+	tid_t		first_tid;
+	unsigned long	blocknr, freed;
+
+	/* OK, work out the oldest transaction remaining in the log, and
+	 * the log block it starts at.
+	 *
+	 * If the log is now empty, we need to work out which is the
+	 * next transaction ID we will write, and where it will
+	 * start. */
+
+	spin_lock(&journal->j_state_lock);
+	spin_lock(&journal->j_list_lock);
+	transaction = journal->j_checkpoint_transactions;
+	if (transaction) {
+		first_tid = transaction->t_tid;
+		blocknr = transaction->t_log_start;
+	} else if ((transaction = journal->j_committing_transaction) != NULL) {
+		first_tid = transaction->t_tid;
+		blocknr = transaction->t_log_start;
+	} else if ((transaction = journal->j_running_transaction) != NULL) {
+		first_tid = transaction->t_tid;
+		blocknr = journal->j_head;
+	} else {
+		first_tid = journal->j_transaction_sequence;
+		blocknr = journal->j_head;
+	}
+	spin_unlock(&journal->j_list_lock);
+	J_ASSERT(blocknr != 0);
+
+	/* If the oldest pinned transaction is at the tail of the log
+           already then there's not much we can do right now. */
+	if (journal->j_tail_sequence == first_tid) {
+		spin_unlock(&journal->j_state_lock);
+		return 1;
+	}
+
+	/* OK, update the superblock to recover the freed space.
+	 * Physical blocks come first: have we wrapped beyond the end of
+	 * the log?  */
+	freed = blocknr - journal->j_tail;
+	if (blocknr < journal->j_tail)
+		freed = freed + journal->j_last - journal->j_first;
+
+	jbd_debug(1,
+		  "Cleaning journal tail from %d to %d (offset %lu), "
+		  "freeing %lu\n",
+		  journal->j_tail_sequence, first_tid, blocknr, freed);
+
+	journal->j_free += freed;
+	journal->j_tail_sequence = first_tid;
+	journal->j_tail = blocknr;
+	spin_unlock(&journal->j_state_lock);
+	if (!(journal->j_flags & JFS_ABORT))
+		jbd2_journal_update_superblock(journal, 1);
+	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 bufers 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 __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.
+ *
+ * This function is called with the journal locked.
+ * This function is called with j_list_lock held.
+ * This function is called with jbd_lock_bh_state(jh2bh(jh))
+ */
+
+int __journal_remove_checkpoint(struct journal_head *jh)
+{
+	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;
+
+	__buffer_unlink(jh);
+	jh->b_cp_transaction = NULL;
+
+	if (transaction->t_checkpoint_list != NULL ||
+	    transaction->t_checkpoint_io_list != NULL)
+		goto out;
+	JBUFFER_TRACE(jh, "transaction has no more buffers");
+
+	/*
+	 * There is one special case to worry about: if we have just pulled the
+	 * buffer off a committing transaction's forget list, then even if the
+	 * checkpoint list is empty, the transaction obviously cannot be
+	 * dropped!
+	 *
+	 * The locking here around j_committing_transaction is a bit sleazy.
+	 * See the comment at the end of journal_commit_transaction().
+	 */
+	if (transaction == journal->j_committing_transaction) {
+		JBUFFER_TRACE(jh, "belongs to committing transaction");
+		goto out;
+	}
+
+	/* OK, that was the last buffer for the transaction: we can now
+	   safely remove this transaction from the log */
+
+	__journal_drop_transaction(journal, transaction);
+
+	/* Just in case anybody was waiting for more transactions to be
+           checkpointed... */
+	wake_up(&journal->j_wait_logspace);
+	ret = 1;
+out:
+	JBUFFER_TRACE(jh, "exit");
+	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 __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);
+
+	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 __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_sync_datalist == 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(transaction->t_updates == 0);
+	J_ASSERT(journal->j_committing_transaction != transaction);
+	J_ASSERT(journal->j_running_transaction != transaction);
+
+	jbd_debug(1, "Dropping transaction %d, all done\n", transaction->t_tid);
+	kfree(transaction);
+}

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