Re: reiserfs and SCSI oops seen in 2.6.9-rc2 with local SCSI disk IO

[Chris Mason <mason@suse.com>]

On Fri, 2004-09-24 at 11:03 -0400, David Wysochanski wrote:
> I can reproduce this pretty easily with local disk.
> 
> Here's some details about my setup (attached is the
> full kernel config):
> - dell 2650 (dual xeon, hyperthreading disabled)
> - 1 local SCSI disk (root volume)
> - 2 local SCSI disks (data), each with 10 partitions
> of 100MB each, 6 of them reiserfs filesystems, 3 of them
> ext3, and 3 of them ext2 (total of 20 unique filesystems)
> - one instance of test program running on each of the
> 20 filesystems
> 
> Sorry, but at this time I can't share the test program itself
> (I'm working on that).  Let me try to describe it though.

I think this is a bug in how reiserfs deals with small filesystems.
There are a few different cases where it will try to use bitmap #2 even
when there is only 1 bitmap.  Each of your test filesystems will need
only 1 bitmap for reiserfs, so while it is a valid bug, it's not the one
you were originally trying to reproduce.

This patch should do it (against 2.6.9-rc3).  Thanks to Jan Kara for
finding this bug.

-chris

On small filesystems (<128M), make sure not to reference bitmap blocks that
don't exist.

Index: linux.269rc3/fs/reiserfs/bitmap.c
===================================================================
--- linux.269rc3.orig/fs/reiserfs/bitmap.c	2004-08-18 09:38:50.000000000 -0400
+++ linux.269rc3/fs/reiserfs/bitmap.c	2004-10-04 20:19:42.000000000 -0400
@@ -236,6 +236,9 @@ static int bmap_hash_id(struct super_blo
 	if (!bm)
 	    bm = 1;
     }
+    /* this can only be true when SB_BMAP_NR = 1 */
+    if (bm >= SB_BMAP_NR(s))
+    	bm = 0;
     return bm;
 }
 
@@ -293,6 +296,10 @@ static int scan_bitmap (struct reiserfs_
 
     get_bit_address (s, *start, &bm, &off);
     get_bit_address (s, finish, &end_bm, &end_off);
+    if (bm > SB_BMAP_NR(s))
+        return 0;
+    if (end_bm > SB_BMAP_NR(s))
+        end_bm = SB_BMAP_NR(s);
 
     /* When the bitmap is more than 10% free, anyone can allocate.
      * When it's less than 10% free, only files that already use the
@@ -313,6 +320,7 @@ static int scan_bitmap (struct reiserfs_
 	    if (nr_allocated)
 		goto ret;
         }
+	/* we know from above that start is a reasonable number */
 	get_bit_address (s, *start, &bm, &off);
     }
 
@@ -1050,9 +1058,10 @@ int reiserfs_allocate_blocknrs(reiserfs_
 {
     int initial_amount_needed = amount_needed;
     int ret;
+    struct super_block *s = hint->th->t_super;
 
     /* Check if there is enough space, taking into account reserved space */
-    if ( SB_FREE_BLOCKS(hint->th->t_super) - REISERFS_SB(hint->th->t_super)->reserved_blocks <
+    if ( SB_FREE_BLOCKS(s) - REISERFS_SB(s)->reserved_blocks <
 	 amount_needed - reserved_by_us)
         return NO_DISK_SPACE;
     /* should this be if !hint->inode &&  hint->preallocate? */
@@ -1072,6 +1081,8 @@ int reiserfs_allocate_blocknrs(reiserfs_
 
     /* find search start and save it in hint structure */
     determine_search_start(hint, amount_needed);
+    if (hint->search_start >= SB_BLOCK_COUNT(s))
+        hint->search_start = SB_BLOCK_COUNT(s) - 1;
 
     /* allocation itself; fill new_blocknrs and preallocation arrays */
     ret = blocknrs_and_prealloc_arrays_from_search_start