Messages in this thread | | | From | Michel Lespinasse <> | Date | Thu, 30 Apr 2020 00:51:02 -0700 | Subject | Re: [RFC][PATCH 1/7] rbtree: Add generic add and find helpers |
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On Thu, Apr 30, 2020 at 12:28 AM Juri Lelli <juri.lelli@redhat.com> wrote: > > --- a/include/linux/rbtree.h > > +++ b/include/linux/rbtree.h > > @@ -141,12 +141,18 @@ static inline void rb_insert_color_cache > > rb_insert_color(node, &root->rb_root); > > } > > > > -static inline void rb_erase_cached(struct rb_node *node, > > +static inline bool rb_erase_cached(struct rb_node *node, > > struct rb_root_cached *root) > > { > > - if (root->rb_leftmost == node) > > + bool leftmost = false; > > + > > + if (root->rb_leftmost == node) { > > root->rb_leftmost = rb_next(node); > > Think we need > > if (root->rb_leftmost) > > > + leftmost = true; > > DEADLINE crashes w/o that.
I think Peter's code is correct; after removing the only node in an rbtree rb_leftmost should be NULL.
The issue appears to be in dequeue_pushable_dl_task unconditionally dereferencing the pointer returned by rb_first_cached(), which may be NULL. I'm not sure what the correct behavior is though, i.e. what dl_rq->earliest_dl.next should be set to if the rbtree ends up empty. Current code (before Peter's changes) preserves the existing dl_rq->earliest_dl.next value in that case, which seems very weird to me (and worthy of a comment if it's correct).
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