On Tue, 2012-08-07 at 11:52 -0400, Bryan Schumaker wrote:
> On 08/07/2012 11:44 AM, Myklebust, Trond wrote:
> > On Tue, 2012-08-07 at 11:30 -0400, bjschuma@xxxxxxxxxx wrote:
> >> From: Bryan Schumaker <bjschuma@xxxxxxxxxx>
> >>
> >> idmap_pipe_downcall already clears this field if the upcall succeeds,
> >> but if it fails (rpc.idmapd isn't running) the field will still be set
> >> on the next call triggering a BUG_ON().
> >>
> >> Signed-off-by: Bryan Schumaker <bjschuma@xxxxxxxxxx>
> >> ---
> >> fs/nfs/idmap.c | 16 +++++++++-------
> >> 1 file changed, 9 insertions(+), 7 deletions(-)
> >>
> >> diff --git a/fs/nfs/idmap.c b/fs/nfs/idmap.c
> >> index b701358..645cfe7 100644
> >> --- a/fs/nfs/idmap.c
> >> +++ b/fs/nfs/idmap.c
> >> @@ -683,10 +683,12 @@ static int nfs_idmap_legacy_upcall(struct key_construction *cons,
> >>
> >> ret = rpc_queue_upcall(idmap->idmap_pipe, msg);
> >> if (ret < 0)
> >> - goto out2;
> >> + goto out3;
> >>
> >> return ret;
> >>
> >> +out3:
> >> + idmap->idmap_key_cons = NULL;
> >> out2:
> >> kfree(im);
> >> out1:
> >
> > That fixes rpc_queue_upcall failure path, but we still need to deal with
> > timeouts and close.
> >
> > How about the following alternative:
> >
> > Set idmap->idmap_key_cons after grabbing the mutex in
> > nfs_idmap_get_key(), then clear it before you release that mutex. That
>
> The key construction data doesn't exist during nfs_idmap_get_key(). request_key() sets it up to pass to our functions as it works through the keyrings code.
OK, however you can still clear idmap_key_cons there...
> > leaves one possible race in which the idmap->idmap_key_cons is cleared
> > while we're in idmap_pipe_downcall. One way to solve that race is to use
> > a second mutex (see the original idmapper design from before your
> > changes) to ensure that nothing clears idmap_key_cons while we're in
> > idmap_pipe_downcall.
This would still apply.
--
Trond Myklebust
Linux NFS client maintainer
NetApp
Trond.Myklebust@xxxxxxxxxx
www.netapp.com
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