-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 Hi,
since commit 7e9c816b (included since qubes-core-dom0 3.2.5)
QubesWatch._register_watches() is called twice for dom0 [0]. This
uncovered that _register_watches() does not handle multiple calls for
dom0 correctly (see commit message for details). This leads to (at
least) two bugs in qubes-manager:
1) qubes-manager misses when a block device becomes available during
runtime of qubes-manager so no notification is shown and you cannot
attached it through the GUI.
2) qubes-manager misses the qrexec startup when a VM is started
externaly (e.g. qvm-start ...). Therefore it thinks qrexec does not
run and for example "Run Command in VM" hangs.
While debugging two things in QubesWatch.__init__ raised my attention:
1) Is _register_watches() intentionally called a second time in L711 for
dom0? (Might be a preparation for not Xen based libvirt backends)
2) L708 should be a 'continue', right?
HW42
[0]: It was already called twice before but _register_watches()
mishandled the libvirt_domain object for dom0, so effectively it was
only called once.
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From f6ccaad77eb7035431e2acafc3031fdcde6465f4 Mon Sep 17 00:00:00 2001 From: HW42 <[email protected]> Date: Sun, 17 Jul 2016 21:35:16 +0200 Subject: [PATCH] QubesWatch: do not create multiple dom0 QubesDB connections When calling _register_watches() multiple times for dom0 (by passing None or since 7e9c816b by passing the corresponding libvirt domain) the check was missing if there is already a QubesDB in _qdb. Therefore a new QubesDB was created and the old one is destroyed by the GC. As a consequence the watch_fd is closed but the libvirt event handle for this fd is still registered. So when libvirt calls poll() it returns immediately POLLNVAL with the closed fd. This is not caught in libvirt and the callback is called as if an event happened. _qdb_handler() now calls read_watch() on the new fd for dom0 and thereby hangs the thread. This leads (at leads) to qubes-manager to miss VM status updates and block device events. --- core/qubesutils.py | 2 ++ 1 file changed, 2 insertions(+) diff --git a/core/qubesutils.py b/core/qubesutils.py index 1f1a4f4..90c2ef8 100644 --- a/core/qubesutils.py +++ b/core/qubesutils.py @@ -761,6 +761,8 @@ class QubesWatch(object): return else: name = "dom0" + if name in self._qdb: + return self._qdb[name] = QubesDB(name) try: self._qdb[name].watch('/qubes-block-devices') -- 2.8.1
0001-QubesWatch-do-not-create-multiple-dom0-QubesDB-conne.patch.sig
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