[linux-cifs-client] [PATCH] Cannot allocate memory

[Pavel Shilovsky]

On Tuesday 10 March 2009 22:01:28 you wrote:
> On Tue, 10 Mar 2009 18:31:36 +0300
>
> Pavel Shilovsky <piastry at etersoft.ru> wrote:
> > Hello!
> >
> > This patch resolves problem "Cannot allocate memory" during loading
> > module when we do unload/load quickly. During unloading the
> > cifs_demultiplex_thread doesn't have enough time for clearing cache and
> > kmem_cache_destroy fails. Then during loading module it fails with
> > kmem_cache_create: duplicate cache cifs_request.
> >
> > This script can show this bug:
> >

> > rmmod cifs
> >
> > for i in `seq 1 20`;
> > do {
> >         echo "trying to mount " $i
> >         insmod ./cifs.ko
> >         cifsmount [имя шары] [путь] -onoperm
Sorry, I forgot to change this line to:
              cifsmount [share name] [path] -onoperm
> >         umount [путь]
> >         rmmod cifs
> > };
> > done
> >
> >
> >
> > And it fails on 2nd iteration.
> >
> > My patch fixes it.
> >
> > diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
> > index 1ae6314..18ba45a 100644
> > --- a/fs/cifs/cifsglob.h
> > +++ b/fs/cifs/cifsglob.h
> > @@ -176,6 +176,7 @@ struct TCP_Server_Info {
> >         struct mac_key mac_signing_key;
> >         char ntlmv2_hash[16];
> >         unsigned long lstrp; /* when we got last response from this
> > server */
> > +       int running;
> >  };
> >
> >  /*
> > diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
> > index f254235..39daaf2 100644
> > --- a/fs/cifs/connect.c
> > +++ b/fs/cifs/connect.c
> > @@ -347,6 +347,7 @@ cifs_demultiplex_thread(struct TCP_Server_Info
> > *server) bool isMultiRsp;
> >         int reconnect;
> >
> > +       server->running = 1;
> >         current->flags |= PF_MEMALLOC;
> >         cFYI(1, ("Demultiplex PID: %d", task_pid_nr(current)));
> >
> > @@ -758,6 +759,8 @@ multi_t2_fnd:
> >
> >         kfree(server->hostname);
> >         task_to_wake = xchg(&server->tsk, NULL);
> > +       server->running = 0;
> > +       msleep(20);
> >         kfree(server);
> >
> >         length = atomic_dec_return(&tcpSesAllocCount);
> > @@ -1408,6 +1411,9 @@ cifs_put_tcp_session(struct TCP_Server_Info
> > *server) task = xchg(&server->tsk, NULL);
> >         if (task)
> >                 force_sig(SIGKILL, task);
> > +
> > +       while(server->running == 1)
> > +               msleep(10);
> >  }
> >
> >  static struct cifsSesInfo *
>
> On what kernel version are you reproducing this? Does it have this patch?
>
> commit 0468a2cf914e79442b8309ce62e3f861599d8cab
> Author: Jeff Layton <jlayton at redhat.com>
> Date:   Mon Dec 1 07:09:35 2008 -0500
>
>     cifs: take module reference when starting cifsd
>
>     cifsd can outlive the last cifs mount. We need to hold a module
>     reference until it exits to prevent someone from unplugging
>     the module until we're ready.
>
>     Signed-off-by: Jeff Layton <jlayton at redhat.com>
>     Signed-off-by: Steve French <sfrench at us.ibm.com>
I have 2.6.27 version of kernel and it doesn't contain this code. I added it 
and tested.
Result: Umounting share finish and when I try to do "rmmod cifs" it says that 
module is in use. I have to wait some time to do it successfully.

My patch provides another behaviour: when umounting share finishes I can remove 
module at once.  

-- 
Best regards,
Pavel Shilovsky.