New: File data corruption when writing to files with DM_EVENT_WRITE enabled over NFS (2.4 kernel)

Seems like someone forgot to send TAKEs to the xfs list once again..

Hmmm - that was a bad one to miss considering the importance of the problem it fixes......

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TAKE 958522 - XFS has conflicting strategies between metadata and file data flushing

Fix to prevent the notorious 'NULL files' problem after a crash.

The problem that has been addressed is that of synchronising updates of the file size with writes that extend a file. Without the fix the update of a file's size, as a result of a write beyond eof, is independent of when the cached data is flushed to disk. Often the file size update would be written to the filesystem log before the data is flushed to disk. When a system crashes between these two events and the filesystem log is replayed on mount the file's size will be set but since the contents never made it to disk the file is full of holes. If some of the cached data was flushed to disk then it may just be a section of the file at the end that has holes.

There are existing fixes to help alleviate this problem, particularly in the case where a file has been truncated, that force cached data to be flushed to disk when the file is closed. If the system crashes while the file(s) are still open then this flushing will never occur.

The fix that we have implemented is to introduce a second file size, called the in-memory file size, that represents the current file size as viewed by the user. The existing file size, called the on-disk file size, is the one that get's written to the filesystem log and we only update it when it is safe to do so. When we write to a file beyond eof we only update the in- memory file size in the write operation. Later when the I/O operation, that flushes the cached data to disk completes, an I/O completion routine will update the on-disk file size. The on-disk file size will be updated to the maximum offset of the I/O or to the value of the in-memory file size if the I/O includes eof.

Date:  Fri Mar 30 02:24:06 AEST 2007
Workarea:  vpn-emea-sw-emea-160-18.emea.sgi.com:/home/lachlan/isms/2.6.x-null
Inspected by:  dgc,tes

The following file(s) were checked into:
longdrop.melbourne.sgi.com:/isms/linux/2.6.x-xfs-melb

Modid: xfs-linux-melb:xfs-kern:28322a
fs/xfs/xfsidbg.c - 1.312 - changed
http://oss.sgi.com/cgi-bin/cvsweb.cgi/xfs-linux/xfsidbg.c.diff?r1=text&tr1=1.312&r2=text&tr2=1.311&f=h
- Fix to prevent the notorious 'NULL files' problem after a crash.

fs/xfs/xfs_vnodeops.c - 1.693 - changed
http://oss.sgi.com/cgi-bin/cvsweb.cgi/xfs-linux/xfs_vnodeops.c.diff?r1=text&tr1=1.693&r2=text&tr2=1.692&f=h
- Fix to prevent the notorious 'NULL files' problem after a crash.

fs/xfs/xfs_iocore.c - 1.52 - changed
http://oss.sgi.com/cgi-bin/cvsweb.cgi/xfs-linux/xfs_iocore.c.diff?r1=text&tr1=1.52&r2=text&tr2=1.51&f=h
- Fix to prevent the notorious 'NULL files' problem after a crash.

fs/xfs/xfs_inode.c - 1.463 - changed
http://oss.sgi.com/cgi-bin/cvsweb.cgi/xfs-linux/xfs_inode.c.diff?r1=text&tr1=1.463&r2=text&tr2=1.462&f=h
- Fix to prevent the notorious 'NULL files' problem after a crash.

fs/xfs/xfs_inode.h - 1.219 - changed
http://oss.sgi.com/cgi-bin/cvsweb.cgi/xfs-linux/xfs_inode.h.diff?r1=text&tr1=1.219&r2=text&tr2=1.218&f=h
- Fix to prevent the notorious 'NULL files' problem after a crash.

fs/xfs/xfs_bmap.c - 1.367 - changed
http://oss.sgi.com/cgi-bin/cvsweb.cgi/xfs-linux/xfs_bmap.c.diff?r1=text&tr1=1.367&r2=text&tr2=1.366&f=h
- Fix to prevent the notorious 'NULL files' problem after a crash.

fs/xfs/xfs_iomap.h - 1.10 - changed
http://oss.sgi.com/cgi-bin/cvsweb.cgi/xfs-linux/xfs_iomap.h.diff?r1=text&tr1=1.10&r2=text&tr2=1.9&f=h
- Fix to prevent the notorious 'NULL files' problem after a crash.

fs/xfs/xfs_iomap.c - 1.52 - changed
http://oss.sgi.com/cgi-bin/cvsweb.cgi/xfs-linux/xfs_iomap.c.diff?r1=text&tr1=1.52&r2=text&tr2=1.51&f=h
- Fix to prevent the notorious 'NULL files' problem after a crash.

fs/xfs/linux-2.6/xfs_lrw.c - 1.259 - changed
http://oss.sgi.com/cgi-bin/cvsweb.cgi/xfs-linux/linux-2.6/xfs_lrw.c.diff?r1=text&tr1=1.259&r2=text&tr2=1.258&f=h
- Fix to prevent the notorious 'NULL files' problem after a crash.

fs/xfs/linux-2.6/xfs_aops.c - 1.142 - changed
http://oss.sgi.com/cgi-bin/cvsweb.cgi/xfs-linux/linux-2.6/xfs_aops.c.diff?r1=text&tr1=1.142&r2=text&tr2=1.141&f=h
- Fix to prevent the notorious 'NULL files' problem after a crash.

fs/xfs/dmapi/xfs_dm.c - 1.34 - changed
http://oss.sgi.com/cgi-bin/cvsweb.cgi/xfs-linux/dmapi/xfs_dm.c.diff?r1=text&tr1=1.34&r2=text&tr2=1.33&f=h
- Fix to prevent the notorious 'NULL files' problem after a crash.

Dave Chinner
Principal Engineer
SGI Australian Software Group