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Marc-André reported an issue on QEMU crash when retrying a cancelled migration during early setup phase, see "Link:" for more information, and also easy way to reproduce. This patch is a replacement of the prior fix proposed by not only switching to migration_cleanup(), but also fixing it from CPR side, so that we track hup_source properly to know if src QEMU is waiting or the HUP signal. To put it simple: this chunk of special casing in migration_cancel() should not affect normal migration, but only cpr-transfer migration to cover the small window when the src QEMU is waiting for a HUP signal on cpr channel (so that src QEMU can continue the migration on the main channel). To achieve that, we'll also need to remember to detach the hup_source whenenver invoked: after that point, we should always be able to cleanup the migration. It's not a generic operation to explicitly detach a gsource from its context while in its dispatch() function. But it should be safe, because gsource disptch() will only happen with a boosted refcount for the dispatcher so that the gsource will not be freed until the callback completes. It's also safe to return G_SOURCE_REMOVE after the gsource is detached, as glib will simply ignore the G_SOURCE_REMOVE. One can refer to latest 2.86.5 glib code in g_main_dispatch() for that: https://github.com/GNOME/glib/blob/2.86.5/glib/gmain.c#L3592 When at this, add a bunch of assertions to make sure nothing surprises us. After this patch applied, the 2nd migration will not crash QEMU, instead it'll be in CANCELLING until the socket connection times out (it will take ~2min on my Fedora default kernel). During this process no 2nd migration will be allowed, and after it timed out migration can be restarted. It's because so far we don't have control over socket_connect_outgoing(), or anything yet managed by a task executed in qio_task_run_in_thread(). Speeding up the cancellation to be left for future. I also tested cpr-transfer by only providing cpr channel not the main channel (with -incoming defer), kickoff migration on source, then cancel it on source directly without providing the main channel. It keeps working. I wanted to add an unit test for that but it'll need to refactor current cpr-transfer tests first; let's leave it for later. Link: https://lore.kernel.org/r/20260417184742.293061-1-marcandre.lureau@redhat.com Reported-by: Marc-André Lureau <marcandre.lureau@redhat.com> Tested-by: Fabiano Rosas <farosas@suse.de> Reviewed-by: Fabiano Rosas <farosas@suse.de> Link: https://lore.kernel.org/r/20260421175820.302795-1-peterx@redhat.com Signed-off-by: Peter Xu <peterx@redhat.com>
=========== QEMU README =========== QEMU is a generic and open source machine & userspace emulator and virtualizer. QEMU is capable of emulating a complete machine in software without any need for hardware virtualization support. By using dynamic translation, it achieves very good performance. QEMU can also integrate with the Xen and KVM hypervisors to provide emulated hardware while allowing the hypervisor to manage the CPU. With hypervisor support, QEMU can achieve near native performance for CPUs. When QEMU emulates CPUs directly it is capable of running operating systems made for one machine (e.g. an ARMv7 board) on a different machine (e.g. an x86_64 PC board). QEMU is also capable of providing userspace API virtualization for Linux and BSD kernel interfaces. This allows binaries compiled against one architecture ABI (e.g. the Linux PPC64 ABI) to be run on a host using a different architecture ABI (e.g. the Linux x86_64 ABI). This does not involve any hardware emulation, simply CPU and syscall emulation. QEMU aims to fit into a variety of use cases. It can be invoked directly by users wishing to have full control over its behaviour and settings. It also aims to facilitate integration into higher level management layers, by providing a stable command line interface and monitor API. It is commonly invoked indirectly via the libvirt library when using open source applications such as oVirt, OpenStack and virt-manager. QEMU as a whole is released under the GNU General Public License, version 2. For full licensing details, consult the LICENSE file. Documentation ============= Documentation can be found hosted online at `<https://www.qemu.org/documentation/>`_. The documentation for the current development version that is available at `<https://www.qemu.org/docs/master/>`_ is generated from the ``docs/`` folder in the source tree, and is built by `Sphinx <https://www.sphinx-doc.org/en/master/>`_. Building ======== QEMU is multi-platform software intended to be buildable on all modern Linux platforms, OS-X, Win32 (via the Mingw64 toolchain) and a variety of other UNIX targets. The simple steps to build QEMU are: .. code-block:: shell mkdir build cd build ../configure make Additional information can also be found online via the QEMU website: * `<https://wiki.qemu.org/Hosts/Linux>`_ * `<https://wiki.qemu.org/Hosts/Mac>`_ * `<https://wiki.qemu.org/Hosts/W32>`_ Submitting patches ================== The QEMU source code is maintained under the GIT version control system. .. code-block:: shell git clone https://gitlab.com/qemu-project/qemu.git When submitting patches, one common approach is to use 'git format-patch' and/or 'git send-email' to format & send the mail to the qemu-devel@nongnu.org mailing list. All patches submitted must contain a 'Signed-off-by' line from the author. Patches should follow the guidelines set out in the `style section <https://www.qemu.org/docs/master/devel/style.html>`_ of the Developers Guide. Additional information on submitting patches can be found online via the QEMU website: * `<https://wiki.qemu.org/Contribute/SubmitAPatch>`_ * `<https://wiki.qemu.org/Contribute/TrivialPatches>`_ The QEMU website is also maintained under source control. .. code-block:: shell git clone https://gitlab.com/qemu-project/qemu-web.git * `<https://www.qemu.org/2017/02/04/the-new-qemu-website-is-up/>`_ A 'git-publish' utility was created to make above process less cumbersome, and is highly recommended for making regular contributions, or even just for sending consecutive patch series revisions. It also requires a working 'git send-email' setup, and by default doesn't automate everything, so you may want to go through the above steps manually for once. For installation instructions, please go to: * `<https://github.com/stefanha/git-publish>`_ The workflow with 'git-publish' is: .. code-block:: shell $ git checkout master -b my-feature $ # work on new commits, add your 'Signed-off-by' lines to each $ git publish Your patch series will be sent and tagged as my-feature-v1 if you need to refer back to it in the future. Sending v2: .. code-block:: shell $ git checkout my-feature # same topic branch $ # making changes to the commits (using 'git rebase', for example) $ git publish Your patch series will be sent with 'v2' tag in the subject and the git tip will be tagged as my-feature-v2. Bug reporting ============= The QEMU project uses GitLab issues to track bugs. Bugs found when running code built from QEMU git or upstream released sources should be reported via: * `<https://gitlab.com/qemu-project/qemu/-/issues>`_ If using QEMU via an operating system vendor pre-built binary package, it is preferable to report bugs to the vendor's own bug tracker first. If the bug is also known to affect latest upstream code, it can also be reported via GitLab. For additional information on bug reporting consult: * `<https://wiki.qemu.org/Contribute/ReportABug>`_ ChangeLog ========= For version history and release notes, please visit `<https://wiki.qemu.org/ChangeLog/>`_ or look at the git history for more detailed information. Contact ======= The QEMU community can be contacted in a number of ways, with the two main methods being email and IRC: * `<mailto:qemu-devel@nongnu.org>`_ * `<https://lists.nongnu.org/mailman/listinfo/qemu-devel>`_ * #qemu on irc.oftc.net Information on additional methods of contacting the community can be found online via the QEMU website: * `<https://wiki.qemu.org/Contribute/StartHere>`_