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

[dai.ngo@oracle.com]

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.

Thanks,
-Dai

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