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Bruce Fields" To: dai.ngo@oracle.com Cc: chuck.lever@oracle.com, linux-nfs@vger.kernel.org Subject: Re: [PATCH RFC 1/1] nfsd: Initial implementation of NFSv4 Courteous Server Message-ID: <20210630013529.GA6200@fieldses.org> References: <20210603181438.109851-1-dai.ngo@oracle.com> <20210628202331.GC6776@fieldses.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org On Mon, Jun 28, 2021 at 09:40:56PM -0700, dai.ngo@oracle.com wrote: > > On 6/28/21 4:39 PM, dai.ngo@oracle.com wrote: > > > >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.... > > One option is to use locks_copy_conflock/nfsd4_fl_get_owner to detect > the lock being copied belongs to a courtesy client and schedule the > laundromat to run to destroy the courtesy client. This option requires > callers of vfs_lock_file to provide the 'conflock' argument. I'm not sure I follow. What's the advantage of doing it this way? > Regarding local lock conflick, do_lock_file_wait calls vfs_lock_file and > just block waiting for the lock to be released. Both of the options > above do not handle the case where the local lock happens before the > v4 client expires and becomes courtesy client. In this case we can not > let the v4 client becomes courtesy client. Oh, good point, yes, we don't want that waiter stuck waiting forever on this expired client.... > We need to have a way to > detect that someone is blocked on a lock owned by the v4 client and > do not allow that client to become courtesy client. One way to handle > this to mark the v4 lock as 'has_waiter', and then before allowing > the expired v4 client to become courtesy client we need to search > all the locks of this v4 client for any lock with 'has_waiter' flag > and disallow it. The part that I don't like about this approach is > having to search all locks of each lockowner of the v4 client for > lock with 'has_waiter'. I need some suggestions here. I'm not seeing a way to do it without iterating over all the client's locks. I don't think you should need a new flag, though, shouldn't !list_empty(&lock->fl_blocked_requests) be enough? --b. > > -Dai > > >> > >>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.