Double borrow in Box::padding_box_size

[Ms2ger]

STR: ./servo http://www.bing.com

Actual: task 'task 'task '<unnamed>' failed at '<unnamed>assertion failed: self.parent.borrow != WRITING && self.parent.borrow != UNUSED<unnamed>' failed at '' failed at 'RefCell<T> already mutably borrowed', ', RefCell<T> already mutably borrowed/src/compiler/rust/src/libstd/cell.rs/src/compiler/rust/src/libstd/cell.rs', :/src/compiler/rust/src/libstd/cell.rs248 ::135135 (sic)

(gdb) bt
#0  std::rt::unwind::Unwinder::begin_unwind::rust_fail () at /src/compiler/rust/src/libstd/rt/global_heap.rs:59
#1  0x00007ffff78c0663 in std::rt::unwind::Unwinder::begin_unwind (cause=..., self=<optimized out>)
    at /src/compiler/rust/src/libstd/rt/unwind.rs:183
#2  0x000000000045ce6a in rt::unwind::begin_unwind::h9db4a7f21e18372aab::v0.0 ()
#3  0x000000000056f471 in cell::RefCell::borrow::he05fa070c281e60fboaC::v0.0 ()
#4  0x000000000056f2cc in cell::RefCell::get::he1b6fbb93682951ePxaB::v0.0 ()
    at /src/components/main/layout/block.rs:1634
#5  0x00000000005979ae in servo::layout::box_::Box::padding_box_size (self=0x7fffd0078d60)
    at /src/components/main/layout/box_.rs:632
#6  0x000000000058598b in servo::layout::block::Flow$BlockFlow::generated_cb_size (self=0x7fffd0078bd0)
    at /src/components/main/layout/block.rs:1476
#7  0x000000000057c224 in servo::layout::block::BlockFlow::containing_block_size (self=0x7fffc005ae90, viewport_size=...)
    at /src/components/main/layout/block.rs:419
#8  0x0000000000572deb in servo::layout::block::WidthAndMarginsComputer$AbsoluteNonReplaced::containing_block_width (self=0x7fffc80a4710, 
    block=0x7fffc005ae90, ctx=0x7fffe8601228) at /src/components/main/layout/block.rs:1927
#9  0x0000000000572ea9 in servo::layout::block::WidthAndMarginsComputer::initial_computed_width<layout::block::AbsoluteNonReplaced> (
    self=0x7fffc80a4710, block=0x7fffc005ae90, parent_flow_width=..., ctx=0x7fffe8601228)
    at /src/components/main/layout/block.rs:1663
#10 0x00000000005726e2 in servo::layout::block::WidthAndMarginsComputer::compute_width_constraint_inputs<layout::block::AbsoluteNonReplaced> (
    self=0x7fffc80a4710, block=0x7fffc005ae90, parent_flow_width=..., ctx=0x7fffe8601228)
    at /src/components/main/layout/block.rs:1590
#11 0x00000000005740ff in servo::layout::block::WidthAndMarginsComputer::compute_used_width<layout::block::AbsoluteNonReplaced> (
    self=0x7fffc80a4710, block=0x7fffc005ae90, ctx=0x7fffe8601228, parent_flow_width=...)
    at /src/components/main/layout/block.rs:1681
#12 0x00000000005816c8 in servo::layout::block::Flow$BlockFlow::assign_widths (self=0x7fffc005ae90, ctx=0x7fffe8601228)
    at /src/components/main/layout/block.rs:1288
#13 0x00000000005ef6e8 in servo::layout::layout_task::PreorderFlowTraversal$AssignWidthsTraversal::process (self=0x7fffe1ff97f8, flow=...)
    at /src/components/main/layout/layout_task.rs:199
#14 0x0000000000649ff8 in servo::layout::parallel::ParallelPreorderFlowTraversal::run_parallel_helper<layout::layout_task::AssignWidthsTraversal<'static>> (self=0x7fffe1ff97f8, unsafe_flow=..., proxy=0x7fffe1ff9980, top_down_func=
    {void (struct (uint,uint,uint), struct util::workqueue::WorkerProxy<,*mut layout::context::LayoutContext,(uint,uint,uint)> *)} 0x7fffe1ff9748, 
    bottom_up_func=
    {void (struct (uint,uint,uint), struct util::workqueue::WorkerProxy<,*mut layout::context::LayoutContext,(uint,uint,uint)> *)} 0x7fffe1ff9740)
    at /src/components/main/layout/parallel.rs:197
#15 0x0000000000649f41 in servo::layout::parallel::ParallelPreorderFlowTraversal$AssignWidthsTraversal::run_parallel (self=0x7fffe1ff97f8, 
    unsafe_flow=..., proxy=0x7fffe1ff9980) at /src/components/main/layout/parallel.rs:223
#16 0x000000000064a61d in servo::layout::parallel::assign_widths (unsafe_flow=..., proxy=0x7fffe1ff9980)
    at /src/components/main/layout/parallel.rs:391
#17 0x000000000060d60b in workqueue::WorkerThread::start::hef848ab645e05bfamOaZ::v0.0 ()
    at /src/components/main/compositing/compositor_layer.rs:257
#18 0x000000000060cc32 in workqueue::WorkQueue::new::anon::expr_fn::KXa7aL ()
    at /src/components/main/compositing/compositor_layer.rs:257
#19 0x00007ffff7009a68 in fn6736 () at /src/compiler/rust/src/libnative/task.rs:85
#20 0x00007ffff79617e8 in finally (self=<optimized out>, dtor=<optimized out>)
    at /src/compiler/rust/src/libstd/unstable/finally.rs:53
#21 fn47863 () at /src/compiler/rust/src/libstd/rt/task.rs:128
#22 0x00007ffff7968edc in rust_try ()
   from /x86_64-unknown-linux-gnu/src/compiler/rust/x86_64-unknown-linux-gnu/stage2/lib/rustc/x86_64-unknown-linux-gnu/lib/libstd-3e5aeb83-0.9.so
#23 0x00007ffff796158e in put<rt::task::Task> (sched=<optimized out>)
    at /src/compiler/rust/src/libstd/rt/local_ptr.rs:102
#24 put (value=<optimized out>) at /src/compiler/rust/src/libstd/rt/local.rs:29
#25 std::rt::task::Task::run (f={void ()} 0x7fffe1ff9ce8, self=<optimized out>)
    at /src/compiler/rust/src/libstd/rt/task.rs:121
#26 0x00007ffff7009688 in fn6725 () at /src/compiler/rust/src/libnative/task.rs:85
#27 0x00007ffff7963374 in rt::thread::thread_start::h1c6c4d06897b01b3ax::v0.9 ()
    at /src/compiler/rust/src/libstd/rt/thread.rs:48
#28 0x00007ffff4c64e9a in start_thread () from /lib/x86_64-linux-gnu/libpthread.so.0
#29 0x00007ffff51733fd in clone () from /lib/x86_64-linux-gnu/libc.so.6
#30 0x0000000000000000 in ?? ()

[larsbergstrom]

This does not happen when parallel layout is disabled (-y 1)