Date: Sun, 25 Sep 2011 15:40:13 GMT From: Robert Millan <rmh@freebsd.org> To: freebsd-bugs@FreeBSD.org Subject: Re: kern/159663: sockets don't work though nullfs mounts Message-ID: <201109251540.p8PFeDcm074567@freefall.freebsd.org>
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The following reply was made to PR kern/159663; it has been noted by GNATS. From: Robert Millan <rmh@freebsd.org> To: FreeBSD-gnats-submit@freebsd.org, freebsd-bugs@freebsd.org Cc: Kostik Belousov <kostikbel@gmail.com>, Adrian Chadd <adrian@freebsd.org>, Josef Karthauser <joe@freebsd.org>, freebsd-fs@freebsd.org Subject: Re: kern/159663: sockets don't work though nullfs mounts Date: Sun, 25 Sep 2011 17:32:27 +0200 2011/9/24 Robert Millan <rmh@freebsd.org>: > I found a thread from 2007 with further discussion about this problem: > > http://lists.freebsd.org/pipermail/freebsd-fs/2007-February/002669.html Hi, I've looked at the situation in a bit more detail, for now only with sockets in mind (not named pipes). My understanding is (please correct me if I'm wrong): - nullfs holds reference counts for each vnode, but sockets have their own mechanism for reference counting (so_count / soref / sorele). vnode reference counting doesn't protect against socket being closed, which would leave a stale pointer in the upper nullfs layer. - Increasing the reference count of the socket itself can't be done in null_nodeget() because this function is merely a getter whose call doesn't indicate any meaningful event. - It's not clear to me that there's any event in time where the socket reference can be increased. If mounting a nullfs were that event, then all existing sockets would be soref'ed but we wouldn't be soref'ing future sockets created in the lower layer after the mount. This doesn't seem correct. - Possible solution: null_nodeget() semantics are replaced with something that actually allows vnodes in the upper layer to be created and destroyed. - Possible solution: upper layer has a memory structure to keep track of which sockets in the lower layer have been soref'ed.
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