+ reiserfs-dont-drop-pg_dirty-when-releasing-sub-page-sized-dirty-file.patch added to -mm tree

+ reiserfs-dont-drop-pg_dirty-when-releasing-sub-page-sized-dirty-file.patch added to -mm tree

[akpm]

The patch titled
     reiserfs: don't drop PG_dirty when releasing sub-page-sized dirty file
has been added to the -mm tree.  Its filename is
     reiserfs-dont-drop-pg_dirty-when-releasing-sub-page-sized-dirty-file.patch

*** Remember to use Documentation/SubmitChecklist when testing your code ***

See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this

------------------------------------------------------
Subject: reiserfs: don't drop PG_dirty when releasing sub-page-sized dirty file
From: Fengguang Wu <wfg@mail.ustc.edu.cn>

This is not a new problem in 2.6.23-git17.  2.6.22/2.6.23 is buggy in the
same way.

Reiserfs could accumulate dirty sub-page-size files until umount time. 
They cannot be synced to disk by pdflush routines or explicit `sync'
commands.  Only `umount' can do the trick.

The direct cause is: the dirty page's PG_dirty is wrongly _cleared_.
Call trace:
	 [<ffffffff8027e920>] cancel_dirty_page+0xd0/0xf0
	 [<ffffffff8816d470>] :reiserfs:reiserfs_cut_from_item+0x660/0x710
	 [<ffffffff8816d791>] :reiserfs:reiserfs_do_truncate+0x271/0x530
	 [<ffffffff8815872d>] :reiserfs:reiserfs_truncate_file+0xfd/0x3b0
	 [<ffffffff8815d3d0>] :reiserfs:reiserfs_file_release+0x1e0/0x340
	 [<ffffffff802a187c>] __fput+0xcc/0x1b0
	 [<ffffffff802a1ba6>] fput+0x16/0x20
	 [<ffffffff8029e676>] filp_close+0x56/0x90
	 [<ffffffff8029fe0d>] sys_close+0xad/0x110
	 [<ffffffff8020c41e>] system_call+0x7e/0x83

Fix the bug by removing the cancel_dirty_page() call. Tests show that
it causes no bad behaviors on various write sizes.

=== for the patient ===
Here are more detailed demonstrations of the problem.

1) the page has both PG_dirty(D)/PAGECACHE_TAG_DIRTY(d) after being written to;
   and then only PAGECACHE_TAG_DIRTY(d) remains after the file is closed.

------------------------------ screen 0 ------------------------------
[T0] root /home/wfg# cat > /test/tiny
[T1] hi
[T2] root /home/wfg#

------------------------------ screen 1 ------------------------------
[T1] root /home/wfg# echo /test/tiny > /proc/filecache
[T1] root /home/wfg# cat /proc/filecache
     # file /test/tiny
     # flags R:referenced A:active M:mmap U:uptodate D:dirty W:writeback O:owner B:buffer d:dirty w:writeback
     # idx   len     state   refcnt
     0       1       ___UD__Bd_      2
[T2] root /home/wfg# cat /proc/filecache
     # file /test/tiny
     # flags R:referenced A:active M:mmap U:uptodate D:dirty W:writeback O:owner B:buffer d:dirty w:writeback
     # idx   len     state   refcnt
     0       1       ___U___Bd_      2

2) note the non-zero 'cancelled_write_bytes' after /tmp/hi is copied.

------------------------------ screen 0 ------------------------------
[T0] root /home/wfg# echo hi > /tmp/hi
[T1] root /home/wfg# cp /tmp/hi /dev/stdin /test
[T2] hi
[T3] root /home/wfg#

------------------------------ screen 1 ------------------------------
[T1] root /proc/4397# cd /proc/`pidof cp`
[T1] root /proc/4713# cat io
     rchar: 8396
     wchar: 3
     syscr: 20
     syscw: 1
     read_bytes: 0
     write_bytes: 20480
     cancelled_write_bytes: 4096
[T2] root /proc/4713# cat io
     rchar: 8399
     wchar: 6
     syscr: 21
     syscw: 2
     read_bytes: 0
     write_bytes: 24576
     cancelled_write_bytes: 4096

//Question: the 'write_bytes' is a bit more than expected ;-)

Tested-by: Maxim Levitsky <maximlevitsky@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
Sort-of-acked-by: Chris Mason <chris.mason@oracle.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/reiserfs/stree.c |    3 ---
 1 file changed, 3 deletions(-)

diff -puN fs/reiserfs/stree.c~reiserfs-dont-drop-pg_dirty-when-releasing-sub-page-sized-dirty-file fs/reiserfs/stree.c
--- a/fs/reiserfs/stree.c~reiserfs-dont-drop-pg_dirty-when-releasing-sub-page-sized-dirty-file
+++ a/fs/reiserfs/stree.c
@@ -1458,9 +1458,6 @@ static void unmap_buffers(struct page *p
 				}
 				bh = next;
 			} while (bh != head);
-			if (PAGE_SIZE == bh->b_size) {
-				cancel_dirty_page(page, PAGE_CACHE_SIZE);
-			}
 		}
 	}
 }
_

Patches currently in -mm which might be from wfg@mail.ustc.edu.cn are

reiserfs-dont-drop-pg_dirty-when-releasing-sub-page-sized-dirty-file.patch

Re: + reiserfs-dont-drop-pg_dirty-when-releasing-sub-page-sized-dirty-file .patch added to -mm tree

[Fengguang Wu]

On Wed, Oct 24, 2007 at 04:07:37PM -0700, akpm@linux-foundation.org wrote:
> 
> The patch titled
>      reiserfs: don't drop PG_dirty when releasing sub-page-sized dirty file
> has been added to the -mm tree.  Its filename is
>      reiserfs-dont-drop-pg_dirty-when-releasing-sub-page-sized-dirty-file.patch
> 
> *** Remember to use Documentation/SubmitChecklist when testing your code ***
> 
> See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
> out what to do about this
> 
> ------------------------------------------------------
> Subject: reiserfs: don't drop PG_dirty when releasing sub-page-sized dirty file
> From: Fengguang Wu <wfg@mail.ustc.edu.cn>
> 
> This is not a new problem in 2.6.23-git17.  2.6.22/2.6.23 is buggy in the
> same way.
> 
> Reiserfs could accumulate dirty sub-page-size files until umount time. 
> They cannot be synced to disk by pdflush routines or explicit `sync'
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Sorry it's not that horrible. The *data* will still be written to disk.
Only the inodes will be stuck in I_DIRTY_PAGES state, and the pages
stuck in PAGECACHE_TAG_DIRTY state.

> commands.  Only `umount' can do the trick.
> 
> The direct cause is: the dirty page's PG_dirty is wrongly _cleared_.
> Call trace:
> 	 [<ffffffff8027e920>] cancel_dirty_page+0xd0/0xf0
> 	 [<ffffffff8816d470>] :reiserfs:reiserfs_cut_from_item+0x660/0x710
> 	 [<ffffffff8816d791>] :reiserfs:reiserfs_do_truncate+0x271/0x530
> 	 [<ffffffff8815872d>] :reiserfs:reiserfs_truncate_file+0xfd/0x3b0
> 	 [<ffffffff8815d3d0>] :reiserfs:reiserfs_file_release+0x1e0/0x340
> 	 [<ffffffff802a187c>] __fput+0xcc/0x1b0
> 	 [<ffffffff802a1ba6>] fput+0x16/0x20
> 	 [<ffffffff8029e676>] filp_close+0x56/0x90
> 	 [<ffffffff8029fe0d>] sys_close+0xad/0x110
> 	 [<ffffffff8020c41e>] system_call+0x7e/0x83
> 
> Fix the bug by removing the cancel_dirty_page() call. Tests show that
> it causes no bad behaviors on various write sizes.