Description of problem: the cifs client code in the kernel sometimes garbles files that are written in append mode.


Version-Release number of selected component (if applicable):
kernel 2.6.18-164.15.1.el5

How reproducible:
This depends on the write mode and probably on the type of SAMBA/CIFS server.

Solution:

I am pretty sure that the problem that we experience is what is described in kernel ChangeLog-2.31.7:
http://www.kernel.org/pub/linux/kernel/v2.6/ChangeLog-2.6.31.7

---> Quoting:
    CIFS: Duplicate data on appending to some Samba servers
    
    commit cea62343956c24452700c06cf028b72414c58a74 upstream.

    SMB writes are sent with a starting offset and length. When the server
    supports the newer SMB trans2 posix open (rather than using the SMB
    NTCreateX) a file can be opened with SMB_O_APPEND flag, and for that
    case Samba server assumes that the offset sent in SMBWriteX is unneeded
    since the write should go to the end of the file - which can cause
    problems if the write was cached (since the beginning part of a
    page could be written twice by the client mm).  Jeff suggested that
    masking the flag on posix open on the client is easiest for the time
    being.

----> End quote

The fix is simple: comment out or remove lines 170 and 171 of fs/cifs/dir.c:

if (oflags & O_APPEND) 
   posix_flags != O_SMB_APPEND

The line above is indeed not present in kernel 2.6.31.7. I recompiled the cifs kernel module and tested and for me this works.