[PATCH] MPSAFE/LOOKUP_SHARED cd9660
John Baldwin
jhb at freebsd.org
Thu Nov 20 14:48:26 PST 2008
On Thursday 20 November 2008 04:30:57 pm Paul B. Mahol wrote:
> On 11/19/08, John Baldwin <jhb at freebsd.org> wrote:
> > This is a relatively simple patch to mark cd9660 MPSAFE and enable shared
> > lookups. The changes to cd9660_lookup() mirror similar changes to
> > ufs_lookup() to use static variables for local data rather than abusing
> > i-node members of the parent directory. I've done some light testing of
> > this, but not super-strenuous. This patch also includes simple locking
for
> > the iconv support in the kernel. That locking uses an sx lock to
serialize
> > open and close of translator tables and the associated refcount. Actual
> > conversions do not need any locks, however as the mount holds a reference
on
> > the table.
> >
> > http://www.FreeBSD.org/~jhb/patches/cd9660_mpsafe.patch
> >
>
> With this patch I'm unable to kldunload libiconv.ko once it is loaded.
> And trying to kldunload libiconv.ko will make any next
kldload/kldstat/kldunload
> to fail waiting forever(livelock).
>
> Regression were not encountered while only cd9660.ko were kldloaded.
So this is actually due to a bug in the module code. If you have two modules
like this:
DECLARE_MODULE(foo, SI_SUB_DRIVERS, SI_ORDER_FIRST);
DECLARE_MODULE(bar, SI_SUB_DRIVERS, SI_ORDER_SECOND);
The SI_* constants ensure that foo's module handler is called before bar's
module handler for MOD_LOAD. However, we don't enforce a reverse order (bar
then foo) for MOD_UNLOAD. In fact, the order of MOD_UNLOAD events is random
and has no relation to the SI_* constants. :(
What is happening here is that one of the 'bar' modules in libiconv.ko is
getting unloaded after 'foo' gets unloaded and using a destroyed lock (you
get a panic if you run with INVARIANTS).
--
John Baldwin
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