Re: NFS/lazy-umount/path-lookup-related panics at shutdown (at kill of processes on lazy-umounted filesystems) with 3.9.2 and 3.9.5

[Nix <nix@esperi.org.uk>]

On 12 Jun 2013, Al Viro outgrape:

> On Wed, Jun 12, 2013 at 01:08:26PM +0100, Nix wrote:
>
>> At this point, we have a sibcall to call_connect() I think. The RPC task
>> of discourse happens to be local, and as the relevant comment says
>> 
>> 		 * We want the AF_LOCAL connect to be resolved in the
>> 		 * filesystem namespace of the process making the rpc
>> 		 * call.  Thus we connect synchronously.
>> 
>> Probably this should be doing this only if said namespace isn't
>> disconnected and going away...
>
> Namespace, shnamespace...  In this case the namespace is alive and well,
> it's just that the process is getting killed and it's already past the
> point where it has discarded all references to root/cwd.

Yeah.

>> > Why is it done in essentially random process context, anyway?  There's such thing
>> > as chroot, after all, which would screw that sucker as hard as NULL ->fs, but in
>> > a less visible way...
>> 
>> I don't think it is a random process context. It's all intentionally
>> done in the context of the process which is the last to close that
>> filesystem, as part of the process of tearing it down -- but it looks
>> like the NFS svcrpc connection code isn't expecting to be called in that
>> situation.
>
> _What_?  Suppose we have something mounted on /jail/net/foo/bar; will the
> effect of process chrooted into /jail doing umount /net/foo/bar be different
> from that of process outside of the jail doing umount /jail/net/foo/bar?

Correction: that comment suggests that it was intentionally done. I
didn't write the comment and I make no judgement on whether it makes
sense or not (it looks like it would *normally* make sense, but I guess
nobody thought of the case of a connection being done as part of
disconnection after the cwd is gone).

I'm just the guy getting bitten by the resulting oops :)

-- 
NULL && (void)