Re: [PATCH] MPSAFE/LOOKUP_SHARED cd9660

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 ....

-- 
Paul