Re: [PATCH RFC 1/1] nfsd: Initial implementation of NFSv4 Courteous Server

dai.ngo
2021-06-28T23:40:24Z

On 6/28/21 1:23 PM, J. Bruce Fields wrote:
> On Thu, Jun 03, 2021 at 02:14:38PM -0400, Dai Ngo wrote:
>> @@ -6875,7 +6947,12 @@ nfsd4_lock(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>> case -EAGAIN: /* conflock holds conflicting lock */
>> status = nfserr_denied;
>> dprintk("NFSD: nfsd4_lock: conflicting lock found!\n");
>> - nfs4_set_lock_denied(conflock, &lock->lk_denied);
>> +
>> + /* try again if conflict with courtesy client */
>> + if (nfs4_set_lock_denied(conflock, &lock->lk_denied) == -EAGAIN && !retried) {
>> + retried = true;
>> + goto again;
>> + }
> Ugh, apologies, this was my idea, but I just noticed it only handles conflicts
> from other NFSv4 clients. The conflicting lock could just as well come from
> NLM or a local process. So we need cooperation from the common locks.c code.
>
> I'm not sure what to suggest....
>
> Maybe something like:
>
> @@ -1159,6 +1159,7 @@ static int posix_lock_inode(struct inode *inode, struct file_lock *request,
> }
>
> percpu_down_read(&file_rwsem);
> +retry:
> spin_lock(&ctx->flc_lock);
> /*
> * New lock request. Walk all POSIX locks and look for conflicts. If
> @@ -1169,6 +1170,11 @@ static int posix_lock_inode(struct inode *inode, struct file_lock *request,
> list_for_each_entry(fl, &ctx->flc_posix, fl_list) {
> if (!posix_locks_conflict(request, fl))
> continue;
> + if (fl->fl_lops->fl_expire_lock(fl, 1)) {
> + spin_unlock(&ctx->flc_lock);
> + fl->fl_lops->fl_expire_locks(fl, 0);
> + goto retry;
> + }
> if (conflock)
> locks_copy_conflock(conflock, fl);
> error = -EAGAIN;
>
>
> where ->fl_expire_lock is a new lock callback with second argument "check"
> where:
>
> check = 1 means: just check whether this lock could be freed
> check = 0 means: go ahead and free this lock if you can

Thanks Bruce, I will look into this approach.

-Dai

>
> --b.