Re: [RFC tip/locking/lockdep v5 06/17] lockdep: Support deadlock detection for recursive read in check_noncircular()
On Thu, Feb 22, 2018 at 04:16:26PM +0100, Peter Zijlstra wrote: > 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 Yep.. I was about to rely you with something similar.. I will add a comment for this function and other "brain-hurting" functions too. Sorry for the headache ;-( Regards, Boqun > does too. signature.asc Description: PGP signature
Re: [RFC tip/locking/lockdep v5 06/17] lockdep: Support deadlock detection for recursive read in check_noncircular()
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.
Re: [RFC tip/locking/lockdep v5 06/17] lockdep: Support deadlock detection for recursive read in check_noncircular()
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)