Re: [PATCH v2] NFSd: fix locking in nfsd_forget_delegations()

[Bryan Schumaker]

On 07/12/2012 11:43 AM, J. Bruce Fields wrote:
> On Fri, May 25, 2012 at 06:38:50PM +0400, Stanislav Kinsbursky wrote:
>> v2: dl_recall_lru list is used for delegations collect because it's modified
>> both in unhash_delegation() and nfsd_break_one_deleg().
>>
>> This patch adds recall_lock hold to nfsd_forget_delegations() to protect
>> nfsd_process_n_delegations() call.
>> Also, looks like it would be better to collect delegations to some local
>> on-stack list, and then unhash collected list. This split allows to
>> simplify locking, because delegation traversing is protected by recall_lock,
>> when delegation unhash is protected by client_mutex.
> 
> Thanks, applying for 3.6 (assuming Bryan doesn't have any objection).

Nope, I don't have any objections.

- Bryan

> 
> --b.
> 
>>
>> Signed-off-by: Stanislav Kinsbursky <skinsbursky@xxxxxxxxxxxxx>
>> ---
>>  fs/nfsd/nfs4state.c |   21 +++++++++++++++++----
>>  1 files changed, 17 insertions(+), 4 deletions(-)
>>
>> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
>> index 21266c7..3d6848b 100644
>> --- a/fs/nfsd/nfs4state.c
>> +++ b/fs/nfsd/nfs4state.c
>> @@ -4694,7 +4694,7 @@ void nfsd_forget_openowners(u64 num)
>>  	printk(KERN_INFO "NFSD: Forgot %d open owners", count);
>>  }
>>  
>> -int nfsd_process_n_delegations(u64 num, void (*deleg_func)(struct nfs4_delegation *))
>> +int nfsd_process_n_delegations(u64 num, struct list_head *list)
>>  {
>>  	int i, count = 0;
>>  	struct nfs4_file *fp, *fnext;
>> @@ -4703,7 +4703,7 @@ int nfsd_process_n_delegations(u64 num, void (*deleg_func)(struct nfs4_delegatio
>>  	for (i = 0; i < FILE_HASH_SIZE; i++) {
>>  		list_for_each_entry_safe(fp, fnext, &file_hashtbl[i], fi_hash) {
>>  			list_for_each_entry_safe(dp, dnext, &fp->fi_delegations, dl_perfile) {
>> -				deleg_func(dp);
>> +				list_move(&dp->dl_recall_lru, list);
>>  				if (++count == num)
>>  					return count;
>>  			}
>> @@ -4716,9 +4716,16 @@ int nfsd_process_n_delegations(u64 num, void (*deleg_func)(struct nfs4_delegatio
>>  void nfsd_forget_delegations(u64 num)
>>  {
>>  	unsigned int count;
>> +	LIST_HEAD(victims);
>> +	struct nfs4_delegation *dp, *dnext;
>> +
>> +	spin_lock(&recall_lock);
>> +	count = nfsd_process_n_delegations(num, &victims);
>> +	spin_unlock(&recall_lock);
>>  
>>  	nfs4_lock_state();
>> -	count = nfsd_process_n_delegations(num, unhash_delegation);
>> +	list_for_each_entry_safe(dp, dnext, &victims, dl_recall_lru)
>> +		unhash_delegation(dp);
>>  	nfs4_unlock_state();
>>  
>>  	printk(KERN_INFO "NFSD: Forgot %d delegations", count);
>> @@ -4727,10 +4734,16 @@ void nfsd_forget_delegations(u64 num)
>>  void nfsd_recall_delegations(u64 num)
>>  {
>>  	unsigned int count;
>> +	LIST_HEAD(victims);
>> +	struct nfs4_delegation *dp, *dnext;
>>  
>>  	nfs4_lock_state();
>>  	spin_lock(&recall_lock);
>> -	count = nfsd_process_n_delegations(num, nfsd_break_one_deleg);
>> +	count = nfsd_process_n_delegations(num, &victims);
>> +	list_for_each_entry_safe(dp, dnext, &victims, dl_recall_lru) {
>> +		list_del(&dp->dl_recall_lru);
>> +		nfsd_break_one_deleg(dp);
>> +	}
>>  	spin_unlock(&recall_lock);
>>  	nfs4_unlock_state();
>>  
>>
>> --
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