Bug#324900: nscd: umount /var fails (unclean shutdowns)

[Zlatko Calusic <zlatko.calusic@iskon.hr>]

Gabor Gombas <gombasg@sztaki.hu> writes:

> Well, if /bin/sh is bash, then it is not weird at all, it is the same
> "bash vs. NSS" problem that came up several times in the past (last time
> quite recently on debian-devel). Previously it only happened with NSS
> modules that link to libraries under /usr, now it also affects nscd.
>
> What I _suspect_ is happening here:
>
> - by calling /etc/init.d/rc, bash is executed
> - bash unconditionally does some NSS calls during startup (getpwuid
>   etc.); this in turn
> - loads all NSS modules that serve passwd maps -> if a module uses
>   libraries from /usr, now you have a live memory mapping under /usr so
>   you cannot unmount it during shutdown
> - bash (libc) connects to nscd
> - nscd sends a file descriptor of /var/db/nscd/passwd to bash, and bash
>   does an mmap(2) on the received fd -> now you have a live memory
>   mapping under /var thus you cannot unmount it during shutdown
> - /etc/init.d/rc eventually kills nscd but that does not help, since the
>   bash process executing /etc/init.d/rc still has the cache file mapped
>   (deleting the cache file also doesn't help since unlink(2) only
>   operates on the directory and does not invalidate the memory mapping)
>

Yes, yes, yes. This is exactly what's happening and you explained it
so nicely I take my hat off and bow in front of you. :) THANKS!

At least we know now what we're dealing with here and I hope some of
your suggestions will be accepted to resolve this intricate problem.


-- 
Zlatko