[PATCH] JBD: plan JBD locking schema

This is the start of the JBD locking rework.

The aims of all this are to remove all lock_kernel() calls from JBD, to
remove all lock_journal() calls (the context switch rate is astonishing when
the lock_kernel()s are removed) and to remove all sleep_on() instances.




The strategy which is taken is:

a) Define the lcoking schema (this patch)

b) Work through every JBD data structure and implement its locking fully,
   according to the above schema.  We work from "innermost" data structures
   and outwards.

It isn't guaranteed that the filesystem will work very well at all stages of
this patch series.



In this patch:


Add commentary and various locks to jbd.h describing the locking scheme which
is about to be implemented.

Initialise the new locks.

Coding-style goodness in jbd.h

fs/jbd/checkpoint.c

@@ -576,7 +576,6 @@ void __journal_drop_transaction(journal_t *journal, transaction_t *transaction)
 			journal->j_checkpoint_transactions = NULL;
 	}
 
-	J_ASSERT (transaction->t_ilist == NULL);
 	J_ASSERT (transaction->t_buffers == NULL);
 	J_ASSERT (transaction->t_sync_datalist == NULL);
 	J_ASSERT (transaction->t_forget == NULL);

fs/jbd/journal.c

@@ -707,6 +707,9 @@ static journal_t * journal_init_common (void)
 	init_MUTEX(&journal->j_barrier);
 	init_MUTEX(&journal->j_checkpoint_sem);
 	init_MUTEX(&journal->j_sem);
+	spin_lock_init(&journal->j_revoke_lock);
+	spin_lock_init(&journal->j_list_lock);
+	spin_lock_init(&journal->j_state_lock);
 
 	journal->j_commit_interval = (HZ * 5);
 

fs/jbd/transaction.c

@@ -58,6 +58,8 @@ static transaction_t * get_transaction (journal_t * journal, int is_try)
 	transaction->t_tid = journal->j_transaction_sequence++;
 	transaction->t_expires = jiffies + journal->j_commit_interval;
 	INIT_LIST_HEAD(&transaction->t_jcb);
+	spin_lock_init(&transaction->t_handle_lock);
+	spin_lock_init(&transaction->t_jcb_lock);
 
 	/* Set up the commit timer for the new transaction. */
 	J_ASSERT (!journal->j_commit_timer_active);

include/linux/journal-head.h

@@ -3,7 +3,7 @@
  *
  * buffer_head fields for JBD
  *
- * 27 May 2001 ANdrew Morton <andrewm@uow.edu.au>
+ * 27 May 2001 Andrew Morton <akpm@digeo.com>
  *	Created - pulled out of fs.h
  */
 
@@ -15,55 +15,70 @@ typedef struct transaction_s	transaction_t;	/* Compound transaction type */
 struct buffer_head;
 
 struct journal_head {
-#ifndef CONFIG_JBD_UNIFIED_BUFFERS
-	/* Points back to our buffer_head. */
+	/*
+	 * Points back to our buffer_head. [jbd_lock_bh_journal_head()]
+	 */
 	struct buffer_head *b_bh;
-#endif
 
-	/* Reference count - see description in journal.c */
+	/*
+	 * Reference count - see description in journal.c
+	 * [jbd_lock_bh_journal_head()]
+	 */
 	int b_jcount;
 
-	/* Journaling list for this buffer */
+	/*
+	 * Journalling list for this buffer [jbd_lock_bh_state()]
+	 */
 	unsigned b_jlist;
 
-	/* Copy of the buffer data frozen for writing to the log. */
-	char * b_frozen_data;
+	/*
+	 * Copy of the buffer data frozen for writing to the log.
+	 * [jbd_lock_bh_state()]
+	 */
+	char *b_frozen_data;
 
-	/* Pointer to a saved copy of the buffer containing no
-           uncommitted deallocation references, so that allocations can
-           avoid overwriting uncommitted deletes. */
-	char * b_committed_data;
+	/*
+	 * Pointer to a saved copy of the buffer containing no uncommitted
+	 * deallocation references, so that allocations can avoid overwriting
+	 * uncommitted deletes. [jbd_lock_bh_state()]
+	 */
+	char *b_committed_data;
 
-	/* Pointer to the compound transaction which owns this buffer's
-           metadata: either the running transaction or the committing
-           transaction (if there is one).  Only applies to buffers on a
-           transaction's data or metadata journaling list. */
-	/* Protected by journal_datalist_lock */
-	transaction_t * b_transaction;
+	/*
+	 * Pointer to the compound transaction which owns this buffer's
+	 * metadata: either the running transaction or the committing
+	 * transaction (if there is one).  Only applies to buffers on a
+	 * transaction's data or metadata journaling list.
+	 * [j_list_lock] [jbd_lock_bh_state()]
+	 */
+	transaction_t *b_transaction;
 
-	/* Pointer to the running compound transaction which is
-           currently modifying the buffer's metadata, if there was
-           already a transaction committing it when the new transaction
-           touched it. */
-	transaction_t * b_next_transaction;
+	/*
+	 * Pointer to the running compound transaction which is currently
+	 * modifying the buffer's metadata, if there was already a transaction
+	 * committing it when the new transaction touched it.
+	 * [t_list_lock] [jbd_lock_bh_state()]
+	 */
+	transaction_t *b_next_transaction;
 
-	/* Doubly-linked list of buffers on a transaction's data,
-           metadata or forget queue. */
-	/* Protected by journal_datalist_lock */
+	/*
+	 * Doubly-linked list of buffers on a transaction's data, metadata or
+	 * forget queue. [jbd_lock_bh_state()]
+	 */
 	struct journal_head *b_tnext, *b_tprev;
 
 	/*
 	 * Pointer to the compound transaction against which this buffer
 	 * is checkpointed.  Only dirty buffers can be checkpointed.
+	 * [j_list_lock]
 	 */
-	/* Protected by journal_datalist_lock */
-	transaction_t * b_cp_transaction;
+	transaction_t *b_cp_transaction;
 
 	/*
 	 * Doubly-linked list of buffers still remaining to be flushed
 	 * before an old transaction can be checkpointed.
+	 * [j_list_lock]
 	 */
-	/* Protected by journal_datalist_lock */
 	struct journal_head *b_cpnext, *b_cpprev;
 };