elevator algorithm in disk controller bad?

@@ -736,9 +736,20 @@
 		   atomic_read(&(jl->j_commit_left)));
   }
 
+  /* make sure all the log blocks are on disk before we flush
+  ** the commit
+  */
+  reiserfs_write_barrier(jl->j_commit_bh) ;
+
   mark_buffer_dirty(jl->j_commit_bh) ;
   ll_rw_block(WRITE, 1, &(jl->j_commit_bh)) ;
   wait_on_buffer(jl->j_commit_bh) ;
+
+  /* make sure the commit is on disk before we allow anyone to start
+  ** writing the metadata
+  */
+  reiserfs_write_barrier(jl->j_commit_bh) ;
+
   if (!buffer_uptodate(jl->j_commit_bh)) {
     reiserfs_panic(s, "journal-615: buffer write failed\n") ;
   }

@@ -820,6 +831,9 @@
   if (trans_id >= SB_JOURNAL(p_s_sb)->j_last_flush_trans_id) {
     if (buffer_locked((SB_JOURNAL(p_s_sb)->j_header_bh)))  {
       wait_on_buffer((SB_JOURNAL(p_s_sb)->j_header_bh)) ;
+      /* no need for write barrier here, whoever locked the header bh
+      ** will do that for us.
+      */
       if (!buffer_uptodate(SB_JOURNAL(p_s_sb)->j_header_bh)) {
         reiserfs_panic(p_s_sb, "journal-699: buffer write failed\n") ;
       }

@@ -833,6 +847,9 @@
     set_bit(BH_Dirty, &(SB_JOURNAL(p_s_sb)->j_header_bh->b_state)) ;
     ll_rw_block(WRITE, 1, &(SB_JOURNAL(p_s_sb)->j_header_bh)) ;
     wait_on_buffer((SB_JOURNAL(p_s_sb)->j_header_bh)) ; 
+
+    reiserfs_write_barrier((SB_JOURNAL(p_s_sb)->j_header_bh)) ; 
+
     if (!buffer_uptodate(SB_JOURNAL(p_s_sb)->j_header_bh)) {
       printk( "reiserfs: journal-837: IO error during journal replay\n" );
       return -EIO ;

@@ -1088,6 +1105,11 @@
   if (flushall) {
     update_journal_header_block(s, (jl->j_start + jl->j_len + 2) % JOURNAL_BLOCK_COUNT, jl->j_trans_id) ;
   }
+  /* upddate_journal_header_block takes care of all the write barrier
+  ** requirements.  If writes from older journal lists get reordered before
+  ** the newest list triggers a flush on the journal header block, log replay
+  ** will fix everything for us.
+  */
   remove_all_from_journal_list(s, jl, 0) ;
   jl->j_len = 0 ;
   atomic_set(&(jl->j_nonzerolen), 0) ;

@@ -1101,6 +1123,10 @@
 } 
 
 
+/* kupdate_one_transaction doesn't need to worry about write
+** barriers at all.  That happens during the cleanups triggered by
+** flush_journal_list
+*/
 static int kupdate_one_transaction(struct super_block *s,
                                     struct reiserfs_journal_list *jl) 
 {

@@ -1747,6 +1773,11 @@
 	    CURRENT_TIME - start) ;
   }
   if (!is_read_only(p_s_sb->s_dev) && 
+       /* _update_journal_header_block is the only place during replay 
+       ** we trigger write barriers.  That's ok, if we crash before we 
+       ** hit this point, the same transactions will be replayed again, 
+       ** fixing any write ordering problems introduced.
+       */
        _update_journal_header_block(p_s_sb, SB_JOURNAL(p_s_sb)->j_start, 
                                    SB_JOURNAL(p_s_sb)->j_last_flush_trans_id))
   {

@@ -9,7 +9,7 @@
 
 O_TARGET := reiserfs.o
 obj-y   := bitmap.o do_balan.o namei.o inode.o file.o dir.o fix_node.o super.o prints.o objectid.o \
-lbalance.o ibalance.o stree.o hashes.o buffer2.o tail_conversion.o journal.o resize.o tail_conversion.o version.o item_ops.o ioctl.o procfs.o
+lbalance.o ibalance.o stree.o hashes.o buffer2.o tail_conversion.o journal.o resize.o tail_conversion.o version.o item_ops.o ioctl.o procfs.o writecache.o
 
 obj-m   := $(O_TARGET)
 

@@ -1918,6 +1918,9 @@
  
 /* ioctl's command */
 #define REISERFS_IOC_UNPACK		_IOW(0xCD,1,long)
+
+/* from writecache.c */
+int reiserfs_write_barrier(struct buffer_head *bh) ;
  			         
 #endif /* _LINUX_REISER_FS_H */
 

@@ -0,0 +1,21 @@
+#include <linux/fs.h>
+#include <linux/ide.h>
+
+/* insert a write barrier on the device for this buffer.  All previous
+** requests will be on disk before the next request is
+*/
+int reiserfs_write_barrier(struct buffer_head *bh) {
+    ide_drive_t *drive ;
+    ide_driver_t *d ;
+
+    /* This won't help on lvm or scsi or software raid */
+    drive = get_info_ptr(bh->b_dev) ;
+    if (drive) {
+	d = drive->driver ;
+        if (d->flushcache && d->flushcache(drive)) {
+	    printk (KERN_INFO "%s: Write Cache FAILED Flushing!\n",drive->name);
+	    return -EIO ;
+	} 
+    }
+    return 0 ;
+}