On Jun 22, 2015 4:37 AM, "Borislav Petkov" <b...@alien8.de> wrote: > > On Thu, Jun 18, 2015 at 12:08:35PM -0700, Andy Lutomirski wrote: > > Low-level arch entries often call notify_die, and it's easy for arch > > code to fail to exit an RCU quiescent state first. Assert that > > we're not quiescent in notify_die. > > > > Signed-off-by: Andy Lutomirski <l...@kernel.org> > > --- > > kernel/notifier.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/kernel/notifier.c b/kernel/notifier.c > > index ae9fc7cc360e..980e4330fb59 100644 > > --- a/kernel/notifier.c > > +++ b/kernel/notifier.c > > @@ -544,6 +544,8 @@ int notrace notify_die(enum die_val val, const char > > *str, > > .signr = sig, > > > > }; > > + rcu_lockdep_assert(rcu_is_watching(), > > + "notify_die called but RCU thinks we're > > quiescent"); > > return atomic_notifier_call_chain(&die_chain, val, &args); > > } > > Ok, we're about to die and we will prepend what would be a more > important splat possibly hinting at the problem is with a lockdep splat. > > I think we should do the assertion and make the rcu_lockdep splat come > last I but don't see how to do this easily from all the notify_die() > call sites. > > Or am I missing something...?
notify_die is misnamed and has little to do with death. It's really just notifying about an exception, and we might end up oopsing, sending a signal, or neither. It's unfortunate that context tracking state isn't nmi-safe, forcing us to differentiate rcu_is_watching (set by rcu_nmi_enter) from ct_state() != CONTEXT_USER. Also, I just realized that this whole series has a minor issue in that there's a race where an IRQ hits after syscall entry but before context tracking. I'll fix it up. (I think the impact is limited to a warning.) --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in Please read the FAQ at http://www.tux.org/lkml/
