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

[dai.ngo@oracle.com]

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?

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.

-Dai