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    SubjectRe: [PATCH] reiserfs: don't drop PG_dirty when releasing sub-page-sized dirty file
    FromPeter Zijlstra <>
    DateTue, 23 Oct 2007 12:07:07 +0200
    [ adding reiserfs devs to the CC ]
    
    On Tue, 2007-10-23 at 15:55 +0800, Fengguang Wu wrote:
    > 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 leave newly created sub-page-size files in dirty state
    > for ever.  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 ;-)
    > 
    > Cc: Maxim Levitsky <maximlevitsky@gmail.com>                                                                           
    > Cc: Peter Zijlstra <peterz@infradead.org>
    > Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
    > ---
    >  fs/reiserfs/stree.c |    3 ---
    >  1 file changed, 3 deletions(-)
    > 
    > --- linux-2.6.24-git17.orig/fs/reiserfs/stree.c
    > +++ linux-2.6.24-git17/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);
    > -			}
    >  		}
    >  	}
    >  }
    > 
    
    -
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