Re: [PATCH 2/2] nfsd: clean up potential nfsd_file refcount leaks in COPY codepath

[Jeff Layton <jlayton@kernel.org>]

On Sat, 2023-01-21 at 11:50 -0800, dai.ngo@oracle.com wrote:
> On 1/21/23 10:56 AM, dai.ngo@oracle.com wrote:
> > 
> > On 1/20/23 3:43 AM, Jeff Layton wrote:
> > > On Thu, 2023-01-19 at 10:38 -0800, dai.ngo@oracle.com wrote:
> > > > On 1/19/23 2:56 AM, Jeff Layton wrote:
> > > > > On Wed, 2023-01-18 at 21:05 -0800, dai.ngo@oracle.com wrote:
> > > > > > On 1/17/23 11:38 AM, Jeff Layton wrote:
> > > > > > > There are two different flavors of the nfsd4_copy struct. One is
> > > > > > > embedded in the compound and is used directly in synchronous 
> > > > > > > copies. The
> > > > > > > other is dynamically allocated, refcounted and tracked in the client
> > > > > > > struture. For the embedded one, the cleanup just involves 
> > > > > > > releasing any
> > > > > > > nfsd_files held on its behalf. For the async one, the cleanup is 
> > > > > > > a bit
> > > > > > > more involved, and we need to dequeue it from lists, unhash it, etc.
> > > > > > > 
> > > > > > > There is at least one potential refcount leak in this code now. 
> > > > > > > If the
> > > > > > > kthread_create call fails, then both the src and dst nfsd_files 
> > > > > > > in the
> > > > > > > original nfsd4_copy object are leaked.
> > > > > > > 
> > > > > > > The cleanup in this codepath is also sort of weird. In the async 
> > > > > > > copy
> > > > > > > case, we'll have up to four nfsd_file references (src and dst for 
> > > > > > > both
> > > > > > > flavors of copy structure). They are both put at the end of
> > > > > > > nfsd4_do_async_copy, even though the ones held on behalf of the 
> > > > > > > embedded
> > > > > > > one outlive that structure.
> > > > > > > 
> > > > > > > Change it so that we always clean up the nfsd_file refs held by the
> > > > > > > embedded copy structure before nfsd4_copy returns. Rework
> > > > > > > cleanup_async_copy to handle both inter and intra copies. Eliminate
> > > > > > > nfsd4_cleanup_intra_ssc since it now becomes a no-op.
> > > > > > > 
> > > > > > > Signed-off-by: Jeff Layton <jlayton@kernel.org>
> > > > > > > ---
> > > > > > >     fs/nfsd/nfs4proc.c | 23 ++++++++++-------------
> > > > > > >     1 file changed, 10 insertions(+), 13 deletions(-)
> > > > > > > 
> > > > > > > diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
> > > > > > > index 37a9cc8ae7ae..62b9d6c1b18b 100644
> > > > > > > --- a/fs/nfsd/nfs4proc.c
> > > > > > > +++ b/fs/nfsd/nfs4proc.c
> > > > > > > @@ -1512,7 +1512,6 @@ nfsd4_cleanup_inter_ssc(struct 
> > > > > > > nfsd4_ssc_umount_item *nsui, struct file *filp,
> > > > > > >         long timeout = msecs_to_jiffies(nfsd4_ssc_umount_timeout);
> > > > > > >             nfs42_ssc_close(filp);
> > > > > > > -    nfsd_file_put(dst);
> > > > > > I think we still need this, in addition to release_copy_files called
> > > > > > from cleanup_async_copy. For async inter-copy, there are 2 reference
> > > > > > count added to the destination file, one from nfsd4_setup_inter_ssc
> > > > > > and the other one from dup_copy_fields. The above nfsd_file_put is 
> > > > > > for
> > > > > > the count added by dup_copy_fields.
> > > > > > 
> > > > > With this patch, the references held by the original copy structure 
> > > > > are
> > > > > put by the call to release_copy_files at the end of nfsd4_copy. That
> > > > > means that the kthread task is only responsible for putting the
> > > > > references held by the (kmalloc'ed) async_copy structure. So, I think
> > > > > this gets the nfsd_file refcounting right.
> > > > Yes, I see. One refcount is decremented by release_copy_files at end
> > > > of nfsd4_copy and another is decremented by release_copy_files in
> > > > cleanup_async_copy.
> > > > 
> > > > > 
> > > > > > >         fput(filp);
> > > > > > >             spin_lock(&nn->nfsd_ssc_lock);
> > > > > > > @@ -1562,13 +1561,6 @@ nfsd4_setup_intra_ssc(struct svc_rqst *rqstp,
> > > > > > >                      &copy->nf_dst);
> > > > > > >     }
> > > > > > >     -static void
> > > > > > > -nfsd4_cleanup_intra_ssc(struct nfsd_file *src, struct nfsd_file 
> > > > > > > *dst)
> > > > > > > -{
> > > > > > > -    nfsd_file_put(src);
> > > > > > > -    nfsd_file_put(dst);
> > > > > > > -}
> > > > > > > -
> > > > > > >     static void nfsd4_cb_offload_release(struct nfsd4_callback *cb)
> > > > > > >     {
> > > > > > >         struct nfsd4_cb_offload *cbo =
> > > > > > > @@ -1683,12 +1675,18 @@ static void dup_copy_fields(struct 
> > > > > > > nfsd4_copy *src, struct nfsd4_copy *dst)
> > > > > > >         dst->ss_nsui = src->ss_nsui;
> > > > > > >     }
> > > > > > >     +static void release_copy_files(struct nfsd4_copy *copy)
> > > > > > > +{
> > > > > > > +    if (copy->nf_src)
> > > > > > > +        nfsd_file_put(copy->nf_src);
> > > > > > > +    if (copy->nf_dst)
> > > > > > > +        nfsd_file_put(copy->nf_dst);
> > > > > > > +}
> > > > > > > +
> > > > > > >     static void cleanup_async_copy(struct nfsd4_copy *copy)
> > > > > > >     {
> > > > > > >         nfs4_free_copy_state(copy);
> > > > > > > -    nfsd_file_put(copy->nf_dst);
> > > > > > > -    if (!nfsd4_ssc_is_inter(copy))
> > > > > > > -        nfsd_file_put(copy->nf_src);
> > > > > > > +    release_copy_files(copy);
> > > > > > >         spin_lock(&copy->cp_clp->async_lock);
> > > > > > >         list_del(&copy->copies);
> > > > > > > spin_unlock(&copy->cp_clp->async_lock);
> > > > > > > @@ -1748,7 +1746,6 @@ static int nfsd4_do_async_copy(void *data)
> > > > > > >         } else {
> > > > > > >             nfserr = nfsd4_do_copy(copy, copy->nf_src->nf_file,
> > > > > > >                            copy->nf_dst->nf_file, false);
> > > > > > > -        nfsd4_cleanup_intra_ssc(copy->nf_src, copy->nf_dst);
> > > > > > >         }
> > > > > > >         do_callback:
> > > > > > > @@ -1811,9 +1808,9 @@ nfsd4_copy(struct svc_rqst *rqstp, struct 
> > > > > > > nfsd4_compound_state *cstate,
> > > > > > >         } else {
> > > > > > >             status = nfsd4_do_copy(copy, copy->nf_src->nf_file,
> > > > > > >                            copy->nf_dst->nf_file, true);
> > > > > > > -        nfsd4_cleanup_intra_ssc(copy->nf_src, copy->nf_dst);
> > > > > > >         }
> > > > > > >     out:
> > > > > > > +    release_copy_files(copy);
> > > > > > >         return status;
> > > > > > >     out_err:
> > > > > > This is unrelated to the reference count issue.
> > > > > > 
> > > > > > Here if this is an inter-copy then we need to decrement the reference
> > > > > > count of the nfsd4_ssc_umount_item so that the vfsmount can be 
> > > > > > unmounted
> > > > > > later.
> > > > > > 
> > > > > Oh, I think I see what you mean. Maybe something like the (untested)
> > > > > patch below on top of the original patch would fix that?
> > > > > 
> > > > > diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
> > > > > index c9057462b973..7475c593553c 100644
> > > > > --- a/fs/nfsd/nfs4proc.c
> > > > > +++ b/fs/nfsd/nfs4proc.c
> > > > > @@ -1511,8 +1511,10 @@ nfsd4_cleanup_inter_ssc(struct 
> > > > > nfsd4_ssc_umount_item *nsui, struct file *filp,
> > > > >           struct nfsd_net *nn = net_generic(dst->nf_net, nfsd_net_id);
> > > > >           long timeout = msecs_to_jiffies(nfsd4_ssc_umount_timeout);
> > > > >    -       nfs42_ssc_close(filp);
> > > > > -       fput(filp);
> > > > > +       if (filp) {
> > > > > +               nfs42_ssc_close(filp);
> > > > > +               fput(filp);
> > > > > +       }
> > > > >              spin_lock(&nn->nfsd_ssc_lo
> > > > >           list_del(&nsui->nsui_list);
> > > > > @@ -1813,8 +1815,13 @@ nfsd4_copy(struct svc_rqst *rqstp, struct 
> > > > > nfsd4_compound_state *cstate,
> > > > >           release_copy_files(copy);
> > > > >           return status;
> > > > >    out_err:
> > > > > -       if (async_copy)
> > > > > +       if (async_copy) {
> > > > >                   cleanup_async_copy(async_copy);
> > > > > +               if (nfsd4_ssc_is_inter(async_copy))
> > > > We don't need to call nfsd4_cleanup_inter_ssc since the thread
> > > > nfsd4_do_async_copy has not started yet so the file is not opened.
> > > > We just need to do refcount_dec(&copy->ss_nsui->nsui_refcnt), unless
> > > > you want to change nfsd4_cleanup_inter_ssc to detect this error
> > > > condition and only decrement the reference count.
> > > > 
> > > Oh yeah, and this would break anyway since the nsui_list head is not
> > > being initialized. Dai, would you mind spinning up a patch for this
> > > since you're more familiar with the cleanup here?
> > 
> > Will do. My patch will only fix the unmount issue. Your patch does
> > the clean up potential nfsd_file refcount leaks in COPY codepath.
> 
> Or do you want me to merge your patch and mine into one?
> 

It probably is best to merge them, since backporters will probably want
both patches anyway. Just make yourself the patch author and keep my S-
o-b line.

> I think we need a bit more cleanup in addition to your patch. When
> kmalloc(sizeof(*async_copy->cp_src), ..) or nfs4_init_copy_state
> fails, the async_copy is not initialized yet so calling cleanup_async_copy
> can be a problem.
> 

Yeah.

It may even be best to ensure that the list_head and such are fully
initialized for both allocated and embedded struct nfsd4_copy's. You
might shave off a few cpu cycles by not doing that, but it makes things
more fragile.

Even better, we really ought to split a lot of the fields in nfsd4_copy
into a different structure (maybe nfsd4_async_copy). Trimming down
struct nfsd4_copy would cut down the size of nfsd4_compound as well
since it has a union that contains it. I was planning on doing that
eventually, but if you want to take that on, then that would be fine
too.

-- 
Jeff Layton <jlayton@kernel.org>