Re: [PATCH] MPSAFE/LOOKUP_SHARED cd9660

On Friday 05 December 2008 04:54:23 pm Paul B. Mahol wrote:
> On 12/5/08, John Baldwin <jhb_at_freebsd.org> wrote:
> > On Friday 05 December 2008 03:56:31 pm Paul B. Mahol wrote:
> >> On 12/5/08, John Baldwin <jhb_at_freebsd.org> wrote:
> >> > On Thursday 20 November 2008 05:47:28 pm John Baldwin wrote:
> >> >> 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).
> >> >
> >> > So this should now be fixed with this commit.  If you could verify that
> >> > iconv
> >> > works ok with the latest kern_module.c I would appreciate it.
> >> >
> >> > Author: jhb
> >> > Date: Fri Dec  5 16:47:30 2008
> >> > New Revision: 185642
> >> > URL: http://svn.freebsd.org/changeset/base/185642
> >> >
> >> > Log:
> >> >   When the SYSINIT() to load a module invokes the MOD_LOAD event
> >> > successfully,
> >> >   move that module to the head of the associated linker file's list of
> >> > modules.
> >> >   The end result is that once all the modules are loaded, they are
> >> > sorted
> > in
> >> >   the reverse of their load order.  This causes the kernel linker to
> > invoke
> >> >   the MOD_QUIESCE and MOD_UNLOAD events in the reverse of the order 
that
> >> >   MOD_LOAD was invoked.  This means that the ordering of MOD_LOAD 
events
> >> > that
> >> >   is set by the SI_* paramters to DECLARE_MODULE() are now honored in
> >> > the
> >> > same
> >> >   order they would be for SYSUNINIT() for the MOD_QUIESCE and 
MOD_UNLOAD
> >> >   events.
> >> >
> >> >   MFC after:    1 month
> >> >
> >> > --
> >> > John Baldwin
> >> >
> >>
> >> Yes it works, I tried hard multiple times kldload/kldunload
> >> {libiconv,cd9660,cd9660_iconv in various order} to livelock/panic it,
> >> but without success.
> >>
> >> FYI following LORs happened:
> >>
> >> lock order reversal:
> >>  1st 0xc4322ce8 isofs (isofs) _at_ /usr/src/sys/kern/vfs_lookup.c:442
> >>  2nd 0xd7d8d740 bufwait (bufwait) _at_ /usr/src/sys/kern/vfs_bio.c:2443
> >>  3rd 0xc4322bdc isofs (isofs) _at_
> >> /usr/src/sys/modules/cd9660/../../fs/cd9660/cd9660_vfsops.c:694
> >
> > This LOR should be addressed in the latest cd9660 locking patches.
> >
> > --
> > John Baldwin
> >
> 
> Oh, why I did not checked new version?
> 
> Yes that LOR have gone, but when doing "ll -R" first time on /mnt
> I got following messages from kernel:
> 
> RRIP without PX field?             x ~ 50 times.
> 
> I see you changed LK_EXCLUSIVE to flags, and with MPSAFE ....

The RRIP stuff is all done in cd9660_vget_internal() under an exclusive lock.  
It could be a property of the ISO image.  "PX" holds permissions (owner, 
etc.).  Do you get the same messages w/o the patch with the same ISO image / 
CD?

-- 
John Baldwin