Messages in this thread Patch in this message | | | Date | Mon, 27 May 2019 17:02:51 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2 1/2] lockdep: Fix OOO unlock when hlocks need merging |
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On Fri, May 24, 2019 at 11:15:08PM +0300, Imre Deak wrote: > > ww_mutex_lock(&ww_lock_a, &ww_ctx); > > mutex_lock(&lock_c); > > ww_mutex_lock(&ww_lock_b, &ww_ctx); > > mutex_unlock(&lock_c); (*)
> triggers the following WARN in __lock_release() when doing the unlock at *: > > DEBUG_LOCKS_WARN_ON(curr->lockdep_depth != depth - 1); > > The problem is that the WARN check doesn't take into account the merging > of ww_lock_a and ww_lock_b which results in decreasing curr->lockdep_depth > by 2 not only 1.
Cute...
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c > index c40fba54e324..967352d32af1 100644 > --- a/kernel/locking/lockdep.c > +++ b/kernel/locking/lockdep.c > @@ -3714,7 +3714,7 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass, > hlock->references = 2; > } > > - return 1; > + return 2; > } > } > > @@ -3920,22 +3920,33 @@ static struct held_lock *find_held_lock(struct task_struct *curr, > } > > static int reacquire_held_locks(struct task_struct *curr, unsigned int depth, > - int idx) > + int idx, bool *first_merged) > { > struct held_lock *hlock; > + int first_idx = idx; > > if (DEBUG_LOCKS_WARN_ON(!irqs_disabled())) > return 0; > > for (hlock = curr->held_locks + idx; idx < depth; idx++, hlock++) { > - if (!__lock_acquire(hlock->instance, > + switch (__lock_acquire(hlock->instance, > hlock_class(hlock)->subclass, > hlock->trylock, > hlock->read, hlock->check, > hlock->hardirqs_off, > hlock->nest_lock, hlock->acquire_ip, > - hlock->references, hlock->pin_count)) > + hlock->references, hlock->pin_count)) { > + case 0: > return 1; > + case 1: > + break; > + case 2: > + *first_merged = idx == first_idx; > + break; > + default: > + WARN_ON(1); > + return 0; > + } > } > return 0; > }
Does it work for you if I change it like so?
--- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -3712,7 +3712,7 @@ static int __lock_acquire(struct lockdep hlock->references = 2; } - return 1; + return 2; } } @@ -3918,22 +3918,33 @@ static struct held_lock *find_held_lock( } static int reacquire_held_locks(struct task_struct *curr, unsigned int depth, - int idx) + int idx, unsigned int *merged) { struct held_lock *hlock; + int first_idx = idx; if (DEBUG_LOCKS_WARN_ON(!irqs_disabled())) return 0; for (hlock = curr->held_locks + idx; idx < depth; idx++, hlock++) { - if (!__lock_acquire(hlock->instance, + switch (__lock_acquire(hlock->instance, hlock_class(hlock)->subclass, hlock->trylock, hlock->read, hlock->check, hlock->hardirqs_off, hlock->nest_lock, hlock->acquire_ip, - hlock->references, hlock->pin_count)) + hlock->references, hlock->pin_count)) { + case 0: return 1; + case 1: + break; + case 2: + *merged += (idx == first_idx); + break; + default: + WARN_ON(1); + return 0; + } } return 0; } @@ -3944,9 +3955,9 @@ __lock_set_class(struct lockdep_map *loc unsigned long ip) { struct task_struct *curr = current; + unsigned int depth, merged = 0 struct held_lock *hlock; struct lock_class *class; - unsigned int depth; int i; if (unlikely(!debug_locks)) @@ -3971,14 +3982,14 @@ __lock_set_class(struct lockdep_map *loc curr->lockdep_depth = i; curr->curr_chain_key = hlock->prev_chain_key; - if (reacquire_held_locks(curr, depth, i)) + if (reacquire_held_locks(curr, depth, i, &merged)) return 0; /* * I took it apart and put it back together again, except now I have * these 'spare' parts.. where shall I put them. */ - if (DEBUG_LOCKS_WARN_ON(curr->lockdep_depth != depth)) + if (DEBUG_LOCKS_WARN_ON(curr->lockdep_depth != depth - merged)) return 0; return 1; } @@ -3986,8 +3997,8 @@ __lock_set_class(struct lockdep_map *loc static int __lock_downgrade(struct lockdep_map *lock, unsigned long ip) { struct task_struct *curr = current; + unsigned int depth, merged = 0; struct held_lock *hlock; - unsigned int depth; int i; if (unlikely(!debug_locks)) @@ -4012,7 +4023,7 @@ static int __lock_downgrade(struct lockd hlock->read = 1; hlock->acquire_ip = ip; - if (reacquire_held_locks(curr, depth, i)) + if (reacquire_held_locks(curr, depth, i, &merged)) return 0; /* @@ -4021,6 +4032,11 @@ static int __lock_downgrade(struct lockd */ if (DEBUG_LOCKS_WARN_ON(curr->lockdep_depth != depth)) return 0; + + /* Merging can't happen with unchanged classes.. */ + if (DEBUG_LOCKS_WARN_ON(merged)) + return 0; + return 1; } @@ -4035,8 +4051,8 @@ static int __lock_release(struct lockdep_map *lock, int nested, unsigned long ip) { struct task_struct *curr = current; + unsigned int depth, merged = 1; struct held_lock *hlock; - unsigned int depth; int i; if (unlikely(!debug_locks)) @@ -4091,14 +4107,15 @@ __lock_release(struct lockdep_map *lock, if (i == depth-1) return 1; - if (reacquire_held_locks(curr, depth, i + 1)) + if (reacquire_held_locks(curr, depth, i + 1, &merged)) return 0; /* * We had N bottles of beer on the wall, we drank one, but now * there's not N-1 bottles of beer left on the wall... + * Pouring two of the bottles together is acceptable. */ - DEBUG_LOCKS_WARN_ON(curr->lockdep_depth != depth-1); + DEBUG_LOCKS_WARN_ON(curr->lockdep_depth != depth - merged); /* * Since reacquire_held_locks() would have called check_chain_key()
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