Commit cc3fc7ec authored by Kirill Smelkov's avatar Kirill Smelkov

context: Fix deadlock when new context is created from already-canceled parent

When _BaseCtx is setting up cancel propagation it locks a parent,
checks for parent.err != nil, and, if it is, calls
ctx._cancel(parent.err) _with_ _holding_ parent.mu. Since _cancel
internally also goes through parents and locks them this was deadlocking
on the second call to parent.mu.lock().

-> Fix it by calling ctx._cancel(err) in the constructor outside of
parent lock.

The bug was there from the beginning - from e9567c7b (context: New
package that mirrors Go's context).
parent 1ec2eba4
......@@ -118,12 +118,14 @@ struct _BaseCtx : _Context, object {
// parent is cancellable - glue to propagate cancel from it to us
_BaseCtx *_parent = dynamic_cast<_BaseCtx *>(parent._ptr());
if (_parent != nil) {
error err = nil;
_parent->_mu.lock();
if (_parent->_err != nil)
ctx._cancel(_parent->_err);
else
err = _parent->_err;
if (err == nil)
_parent->_children.insert(bctx);
_parent->_mu.unlock();
if (err != nil)
ctx._cancel(err);
}
else {
if (_ready(pdone))
......
# -*- coding: utf-8 -*-
# Copyright (C) 2019 Nexedi SA and Contributors.
# Copyright (C) 2019-2021 Nexedi SA and Contributors.
# Kirill Smelkov <kirr@nexedi.com>
#
# This program is free software: you can Use, Study, Modify and Redistribute
......@@ -265,6 +265,43 @@ def test_deadline():
assertCtx(ctx, Z, deadline=d, err=D, done=Y)
# test_already_canceled verifies context creation from already canceled parent.
# this used to deadlock.
def test_already_canceled():
parent, pcancel = context.with_cancel(bg)
assertCtx(parent, Z)
pcancel()
assertCtx(parent, Z, err=C, done=Y)
ctxC, _ = context.with_cancel(parent)
assert ctxC.done() != parent.done()
assertCtx(parent, Z, err=C, done=Y) # no ctxC in children
assertCtx(ctxC, Z, err=C, done=Y)
ctxT, _ = context.with_timeout(parent, 10*dt)
d = ctxT.deadline()
assert ctxT.done() != parent.done()
assertCtx(parent, Z, err=C, done=Y) # no ctxT in children
assertCtx(ctxT, Z, deadline=d, err=C, done=Y)
d = time.now() + 10*dt
ctxD, _ = context.with_deadline(parent, d)
assert ctxD.done() != parent.done()
assertCtx(parent, Z, err=C, done=Y) # no ctxD in children
assertCtx(ctxD, Z, deadline=d, err=C, done=Y)
ctxM, _ = context.merge(parent, bg)
assert ctxM.done() != parent.done()
assertCtx(parent, Z, err=C, done=Y) # no ctxM in children
assertCtx(ctxM, Z, err=C, done=Y)
ctxV = context.with_value(parent, kHello, "world")
assert ctxV.done() == parent.done()
assert ctxV.value(kHello) == "world"
assertCtx(parent, Z, err=C, done=Y) # no ctxV in children
assertCtx(ctxV, Z, err=C, done=Y)
# ---- misc ----
# _ready returns whether channel ch is ready.
......
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