svn commit: r254309 - in head: share/man/man9 sys/cddl/contrib/opensolaris/uts/common/dtrace sys/cddl/dev/dtrace sys/cddl/dev/sdt sys/kern sys/sys

[Mark Johnston]

On Wed, Aug 14, 2013 at 8:19 AM, John Baldwin <jhb at freebsd.org> wrote:

> On Tuesday, August 13, 2013 8:42:22 pm Mark Johnston wrote:
> > Author: markj
> > Date: Wed Aug 14 00:42:21 2013
> > New Revision: 254309
> > URL: http://svnweb.freebsd.org/changeset/base/254309
> >
> > Log:
> >   Use kld_{load,unload} instead of mod_{load,unload} for the linker file
> load
> >   and unload event handlers added in r254266.
> >
> >   Reported by:        jhb
> >   X-MFC with: r254266
>
> Thanks!  BTW, it would be really nice to replace HWPMC_HOOKS in
> kern_linker.c with
> EVENTHANDLER calls.  I think kld_load would just work (though you might
> need to
> downgrade the lock before you run it).  For kld_unload it seems you want
> two events,
> a kld_unload_try for your newly added event (since it can reject a
> kld_unload), and
> perhaps kld_unload at the end where the current HWPMC_HOOK is.  Just an
> idea if
> someone is looking for something to do.  I know there are other modules
> that need
> to hook into linker events like this, and making HWPMC_HOOKS more generic
> would be
> a big help.
>

I will look into doing this. The DTrace SDT kld_load handler will not work
properly if the
linker lock is downgraded first because of the following code in
linker_file_lookup_set():

locked = KLD_LOCK();
if (!locked)
        KLD_LOCK();

In particular, it checks to see if the kld lock is exclusively held and
locks it if not, which
obviously causes problems if the thread holds the shared lock.

The answer might be to just run the hwpmc handler with the exclusive lock
held. Or perhaps
we just need a linker_file_lookup_set_locked(), assuming that it's ok to
look up a linker set
with the shared lock held.

-Mark