LMB removal is completed only when the spapr_lmb_release callback
is called after all DRCs of the dimm are detached. During this
time, it is possible that a unplug request for the same dimm
arrives, trying to detach DRCs that were detached by the guest
in the first unplug_request.
BQL doesn't help in this case - the lock will prevent any concurrent
removal from happening until the end of spapr_memory_unplug_request
only. What happens is that the second unplug_request ends up calling
spapr_drc_detach in a DRC that were detached already, causing an
assert error in spapr_drc_detach (e.g
https://bugs.launchpad.net/qemu/+bug/1718118).
spapr_lmb_release uses a structure called sPAPRDIMMState, stored in the
spapr->pending_dimm_unplugs QTAIL, to track how many LMB DRCs are left
to be detached by the guest. When there are no more DRCs left, this
structure is deleted and the pc-dimm unplug handler is called to
finish the process.
This patch reuses the sPAPRDIMMState to allow unplug_request to know
if there is an ongoing unplug process for a given dimm, aborting the
unplug request in this case, by doing the following changes:
- in spapr_lmb_release callback, move the dimm state removal to the
end, after pc-dimm unplug handler. With this change we can check for
the existence of the dimm state to see if the unplug process is
done.
- use spapr_pending_dimm_unplugs_find in spapr_memory_unplug_request
to check if the dimm state exists. If positive, there is an unplug
operation already in progress for this dimm, meaning that we should
abort it and warn the user about it.
Fixes: https://bugs.launchpad.net/qemu/+bug/1718118
Signed-off-by: Daniel Henrique Barboza <danielhb@linux.vnet.ibm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
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.
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:
mkdir build
cd build
../configure
make
Additional information can also be found online via the QEMU website:
http://qemu-project.org/Hosts/Linux
http://qemu-project.org/Hosts/Mac
http://qemu-project.org/Hosts/W32
Submitting patches
==================
The QEMU source code is maintained under the GIT version control system.
git clone git://git.qemu-project.org/qemu.git
When submitting patches, the preferred 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 HACKING and CODING_STYLE files.
Additional information on submitting patches can be found online via
the QEMU website
http://qemu-project.org/Contribute/SubmitAPatch
http://qemu-project.org/Contribute/TrivialPatches
Bug reporting
=============
The QEMU project uses Launchpad as its primary upstream bug tracker. Bugs
found when running code built from QEMU git or upstream released sources
should be reported via:
https://bugs.launchpad.net/qemu/
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 launchpad.
For additional information on bug reporting consult:
http://qemu-project.org/Contribute/ReportABug
Contact
=======
The QEMU community can be contacted in a number of ways, with the two
main methods being email and IRC
- qemu-devel@nongnu.org
http://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:
http://qemu-project.org/Contribute/StartHere
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