Re: mkstemp fails on cifs linux-2.6.31-rc1 / samba-3.3.6

On Tue, 2009-06-30 at 08:27 -0500, Shirish Pargaonkar wrote:
> On Tue, Jun 30, 2009 at 8:01 AM, Jeff Layton<[email protected]> wrote:
> > On Tue, 2009-06-30 at 13:00 +0200, Wilhelm Meier wrote:
> >> Hi,
> >>
> >> I made a simple test with cifs in linux-2.6.31-rc1 to see if the so called
> >> kmail-problem (cifs-user-homes are totally unusable for kmail-mail-cache)
> >> still remains. Than I ran into a strange problem using "sed -i <command> <file-
> >> on-cifs>". "sed" uses mkstemp libc-funktion and fails with EEXIST, writing
> >> therefore tons of files onto the cifs-share.
> >>
> >> You can reproduce it with:
> >>
> >> strace mktemp -p . abcXXXXXX 2>&1 | more
> >>
> >> giving
> >>
> >> stat64(".", {st_mode=S_IFDIR|0700, st_size=0, ...}) = 0
> >> open("./abcUJcKWM", O_RDWR|O_CREAT|O_EXCL, 0600) = -1 EEXIST (File exists)
> >> stat64(".", {st_mode=S_IFDIR|0700, st_size=0, ...}) = 0
> >> open("./abcUGJaiA", O_RDWR|O_CREAT|O_EXCL, 0600) = -1 EEXIST (File exists)
> >> stat64(".", {st_mode=S_IFDIR|0700, st_size=0, ...}) = 0
> >> open("./abcWfKacs", O_RDWR|O_CREAT|O_EXCL, 0600) = -1 EEXIST (File exists)
> >> stat64(".", {st_mode=S_IFDIR|0700, st_size=0, ...}) = 0
> >> open("./abcBaGjWM", O_RDWR|O_CREAT|O_EXCL, 0600) = -1 EEXIST (File exists)
> >>
> >> This is the same on 2.6.31-rc1-git6.
> >>
> >> This is not the case in 2.6.26-2-vserver-686 (debian).
> >>
> >> The Samba-Server is lenny with samba-enterprise:
> >> kmux-fs:/# dpkg -l | grep samba
> >> ii  sernet-samba                    3.3.6-24                 a LanManager-like
> >> file and printer server fo
> >> ii  sernet-samba-common             3.3.6-24                 Samba common files
> >> used by both the server a
> >> ii  sernet-samba-keyring            1.1                      GnuPG archive
> >> keys of the SerNet Samba archi
> >>
> >> If I change Samba to the lenny-version
> >>
> >> ii  samba                           2:3.2.5-4lenny6          a LanManager-like
> >> file and printer server fo
> >> ii  samba-common                    2:3.2.5-4lenny6          Samba common files
> >> used by both the server a
> >>
> >> the described test-case is fine.
> >>
> >>
> >
> > I can reproduce this too.
> >
> > Looks like another regression from the create-on-lookup patches. I
> > commented the relevant chunk out of cifs_lookup and that fixes the
> > issue.
> >
> > Shirish, thoughts?
> >
> > --
> > Jeff Layton <[email protected]>
> >
> >
> 
> Jeff, Wilhelm,
> 
> I will spend some time later in the day on this but one thought came to mind,
> Jeff, we took out a line where if there was exclusive create, we would let
> vfs handle it, not sure if putting it back would help!
> 

Probably...it does seem to be related to O_EXCL. Rather than just
blindly putting that back though, I'd like to see some understanding
about why this is failing, and a consistent idea about how this is code
is intended to work.

Skipping create on lookup for the O_EXCL case seems ass-backwards to me.
Doing it on lookup should help atomicity, and that's just what you want
for O_EXCL.

-- 
Jeff Layton <[email protected]>