From: "J. Bruce Fields" Subject: Re: [PATCH] NLM: hold BKL when clearing global lockd task and serv vars Date: Mon, 7 Apr 2008 16:50:27 -0400 Message-ID: <20080407205027.GE11219@fieldses.org> References: <1207575514-6703-1-git-send-email-jlayton@redhat.com> <1207575514-6703-2-git-send-email-jlayton@redhat.com> <20080407164500.GA17728@infradead.org> <20080407175615.GD3305@fieldses.org> <20080407162241.0a06fd6f@tleilax.poochiereds.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Cc: linux-nfs@vger.kernel.org, nfsv4@linux-nfs.org To: Jeff Layton Return-path: In-Reply-To: <20080407162241.0a06fd6f@tleilax.poochiereds.net> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: nfsv4-bounces@linux-nfs.org Errors-To: nfsv4-bounces@linux-nfs.org List-ID: On Mon, Apr 07, 2008 at 04:22:41PM -0400, Jeff Layton wrote: > On Mon, 7 Apr 2008 13:56:15 -0400 > "J. Bruce Fields" wrote: > > > On Mon, Apr 07, 2008 at 12:45:01PM -0400, Christoph Hellwig wrote: > > > On Mon, Apr 07, 2008 at 09:38:34AM -0400, Jeff Layton wrote: > > > > The global task and serv pointers for lockd are normally protected by > > > > the nlmsvc_mutex. The exception is when the lockd exits abnormally. When > > > > this occurs, these variables are cleared without any locking. > > > > > > Shouldn't we get rid of the case where it exits abnormally instead? > > > > I tried to figure out when this could actually occur (when can > > svc_recv() return an error other than -EINTR or -EAGAIN?), and got lost > > in sock_recvmsg(): > > > > - svc_recv() itself returns only -EAGAIN or the return from > > ->xpo_recvfrom(). > > - the only xpo_recvfrom() that's interesting is > > svc_tcp_recvfrom(), which can return the error it gets from > > svc_recvfrom(), which can return the error from > > kernel_recvmsg(), which gets its return from sock_recvmsg(). > > > > Since __sock_recvmsg() has a security hook, it looks like we can end up > > with an -EACCES from selinux? > > > > So one case would be selinux deciding we weren't allowed to receive > > packets from this socket. Huh. > > I got lost there too, but I would suspect that there are other errors > that can bubble up from the lower networking layers as well. Even if > there aren't currently, it's probably still prudent to assume that it's > a possibility and code for it. > > I tend to think the safest thing is probably to do a long sleep (1s or > so and retry when we get an error (maybe also a ratelimited printk?). Yeah, I guess I can't think of anything better. --b. > It's unlikely to do any harm (other than a few wasted CPU cycles), and > if the error is transient then we have the possibility to recover and > continue normal operation.