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

[dai.ngo@oracle.com]

On 1/21/23 12:12 PM, Chuck Lever III wrote:
>
>> On Jan 21, 2023, at 3:05 PM, Jeff Layton <jlayton@kernel.org> wrote:
>>
>> 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.
> Unless these two changes are somehow interdependent, I'd like to keep
> them separate. They address two separate issues, yes?

Yes.

>
> And -- narrow fixes need to go to nfsd-fixes, but clean-ups can wait
> for nfsd-next. I'd rather not mix the two types of change.

Ok. Can we do this:

1. Jeff's patch goes to nfsd-fixes since it has the fix for missing
reference count.

2. My fix for the cleanup of allocated memory goes to nfsd-fixes.

3. I will do the optimization Jeff proposed about list_head and
nfsd4_compound in a separate patch that goes into nfsd-next.

-Dai

>> 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>
> --
> Chuck Lever
>
>
>