svn commit: r238907 - projects/calloutng/sys/kern

[Konstantin Belousov]

On Sat, Sep 08, 2012 at 06:14:41PM +0100, Attilio Rao wrote:
> On Sat, Sep 8, 2012 at 4:38 PM, Konstantin Belousov <kostikbel at gmail.com> wrote:
> > On Fri, Sep 07, 2012 at 11:35:15PM +0100, Attilio Rao wrote:
> >> On Mon, Jul 30, 2012 at 9:39 PM, Attilio Rao <attilio at freebsd.org> wrote:
> >> > On Mon, Jul 30, 2012 at 4:31 PM, Andriy Gapon <avg at freebsd.org> wrote:
> >> >> on 30/07/2012 18:04 Attilio Rao said the following:
> >> >>> On 7/30/12, Andriy Gapon <avg at freebsd.org> wrote:
> >> >>>> on 30/07/2012 17:56 Attilio Rao said the following:
> >> >>>>> More explicitly, I think such combination TDP_NOSLEEPING +
> >> >>>>> TDP_NOBLOCKING (name invented) should be set on entering the interrupt
> >> >>>>> context, not only related to this part of callouts. This would be a
> >> >>>>> very good help for catching buggy situations.
> >> >>>>
> >> >>>> Something very tangential.  I think it would also be nice to check if a
> >> >>>> thread has
> >> >>>> any(?) locks held when returning to userland.
> >> >>>
> >> >>> This happens already for INVARIANTS case, with td_locks counters.
> >> >>> In the !INVARIANTS case, this doesn't happen because you don't want to
> >> >>> add the burden to bump td_locks for the fast case and I think it is a
> >> >>> good approach.
> >> >>
> >> >> Ah, I missed that, thank you.
> >> >> BTW, it seems that td_locks is checked twice in normal syscallret() path: once in
> >> >> syscallret() itself and then in userret().  On this note, would it make sense to
> >> >> move the whole nine yards of asserts from syscallret() to userret()?
> >> >> I mean it might make sense to have those checks (td_critnest, td_pflags) in other
> >> >> paths to userland.
> >> >
> >> > Nice catch.
> >> > The checks were added to syscallret() in r208453. While this is fine,
> >> > I think that putting them in userret() may give them more exposure and
> >> > cover also cases like traps which are not covered right now.
> >> > If you want to make a patch that moves these conditions in userret()
> >> > I'd be in favor of it.
> >>
> >> More specifically, what do you think about this patch?:
> >> http://www.freebsd.org/~attilio/userret_diag.patch
> >>
> >> Of course I moved the XEN par too before the checks.
> >> The patch survived to few consecutive and parallel buildworlds, FWIW.
> >
> > At least in fork_return(), the last assert which checks that Giant is not
> > held, is no longer needed.
> 
> Actually, this is unnecessary also with -CURRENT stock code today,
> because userret() already checks for td_locks. And it seems
> fork_return() is not the only function where this happens, as trap()
> did this too on x86 and possibly all the other architectures grew it
> with cut&paste. Possibly we need this further, separate, patch before
> userred_diag:
> http://www.freebsd.org/~attilio/userret_nogiant.patch
Yes, this looks good. I suggest to move #ifdef XEN part of the userret()
to befire KASSERT(td->td_locks == 0).

> 
> > I had similar thought from the time when I added TDP_NOFAULTING check to the
> > syscallret(), but the loss of the syscall name in the panic output always
> > stopped me.
> 
> I think in case of a lock/td_pinned/td_critnest/etc. leak, having the
> syscall number in the panic message won't change anything as you will
> likely need a coredump and possibly instrument your kernel with
> further debugging, etc. to see what's going on.

For me, when I debugged TDP_NOFAULTING (which indeed leaked in the
intermediate versions of the patch) the syscall name appeared to be enough.
But, I do not object strongly.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 196 bytes
Desc: not available
Url : http://lists.freebsd.org/pipermail/svn-src-projects/attachments/20120908/302fa7fb/attachment.pgp