Messages in this thread | | | Date | Thu, 22 Feb 2018 16:16:26 +0100 | From | Peter Zijlstra <> | Subject | Re: [RFC tip/locking/lockdep v5 06/17] lockdep: Support deadlock detection for recursive read in check_noncircular() |
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On Thu, Feb 22, 2018 at 03:54:34PM +0100, Peter Zijlstra wrote: > On Thu, Feb 22, 2018 at 03:08:53PM +0800, Boqun Feng wrote: > > > +static inline int hlock_conflict(struct lock_list *entry, void *data) > > +{ > > + struct held_lock *hlock = (struct held_lock *)data; > > + > > + return hlock_class(hlock) == entry->class && > > + (hlock->read != 2 || !entry->is_rr); > > +} > > Bah, brain hurts. > > So before we add prev -> this, relation, we check if there's a this -> > prev relation already in the graph -- if so that would be a problem. > > The above function has @data == @prev (__bfs_forward starts at @this, > looking for @prev), and the above patch augments the 'class_equal' test > with @prev not having read==2 or @entry not having xr; > > This is because.... (insert brain hurt)
(hlock->read != 2 || !entry->have_xr) := !(hlock->read == 2 && entry->have_xr)
hlock->read == 2 := prev->read == 2 entry->have_xr means the last fwd link has read==2.
Together this gives that:
@prev (Rx) ---> X ---> @entry (xR)
does not form a cycle, because:
@enrty (xR) -> @prev (Rx)
is not strong and can be ignored.
Did I get that right? If so, the Changelog needs serious help and code does too.
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