qemu/stubs
Paolo Bonzini 5f50be9b58 async: the main AioContext is only "current" if under the BQL
If we want to wake up a coroutine from a worker thread, aio_co_wake()
currently does not work.  In that scenario, aio_co_wake() calls
aio_co_enter(), but there is no current AioContext and therefore
qemu_get_current_aio_context() returns the main thread.  aio_co_wake()
then attempts to call aio_context_acquire() instead of going through
aio_co_schedule().

The default case of qemu_get_current_aio_context() was added to cover
synchronous I/O started from the vCPU thread, but the main and vCPU
threads are quite different.  The main thread is an I/O thread itself,
only running a more complicated event loop; the vCPU thread instead
is essentially a worker thread that occasionally calls
qemu_mutex_lock_iothread().  It is only in those critical sections
that it acts as if it were the home thread of the main AioContext.

Therefore, this patch detaches qemu_get_current_aio_context() from
iothreads, which is a useless complication.  The AioContext pointer
is stored directly in the thread-local variable, including for the
main loop.  Worker threads (including vCPU threads) optionally behave
as temporary home threads if they have taken the big QEMU lock,
but if that is not the case they will always schedule coroutines
on remote threads via aio_co_schedule().

With this change, the stub qemu_mutex_iothread_locked() must be changed
from true to false.  The previous value of true was needed because the
main thread did not have an AioContext in the thread-local variable,
but now it does have one.

Reported-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210609122234.544153-1-pbonzini@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Tested-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
[eblake: tweak commit message per Vladimir's review]
Signed-off-by: Eric Blake <eblake@redhat.com>
2021-06-18 10:59:52 -05:00
..
arch_type.c stubs: Add arch_type 2020-03-06 17:15:38 +01:00
bdrv-next-monitor-owned.c Include qemu-common.h exactly where needed 2019-06-12 13:20:20 +02:00
blk-commit-all.c Include qemu-common.h exactly where needed 2019-06-12 13:20:20 +02:00
blk-exp-close-all.c block: move block exports to libblockdev 2020-10-23 13:42:16 +01:00
blockdev-close-all-bdrv-states.c all: Clean up includes 2016-02-16 14:29:28 +00:00
change-state-handler.c sysemu: Split sysemu/runstate.h off sysemu/sysemu.h 2019-08-16 13:37:36 +02:00
cmos.c stubs/cmos: Use correct include 2020-09-01 09:10:58 +02:00
cpu-get-clock.c cpu-timers, icount: new modules 2020-10-05 16:41:22 +02:00
cpu-synchronize-state.c cpus: prepare new CpusAccel cpu accelerator interface 2020-10-05 16:41:22 +02:00
cpus-get-virtual-clock.c cpus: prepare new CpusAccel cpu accelerator interface 2020-10-05 16:41:22 +02:00
dump.c Include qemu-common.h exactly where needed 2019-06-12 13:20:20 +02:00
error-printf.c Include qemu-common.h exactly where needed 2019-06-12 13:20:20 +02:00
fdset.c monitor: simplify functions for getting a dup'd fdset entry 2020-09-16 10:33:48 +01:00
fw_cfg.c hw/nvram/fw_cfg: Add fw_cfg_arch_key_name() 2019-05-23 14:10:31 +02:00
gdbstub.c Clean up includes some more 2016-03-22 22:20:16 +01:00
get-vm-name.c stubs: Clean up includes 2016-02-04 17:01:04 +00:00
icount.c icount: rename functions to be consistent with the module name 2020-10-05 16:41:22 +02:00
io_uring.c stubs: add stubs for io_uring interface 2020-01-30 20:59:41 +00:00
iothread-lock.c async: the main AioContext is only "current" if under the BQL 2021-06-18 10:59:52 -05:00
is-daemonized.c Include qemu-common.h exactly where needed 2019-06-12 13:20:20 +02:00
isa-bus.c stubs: add isa_create_simple 2020-07-06 17:01:11 +02:00
linux-aio.c linux-aio: properly bubble up errors from initialization 2018-06-27 13:06:34 +01:00
meson.build async: the main AioContext is only "current" if under the BQL 2021-06-18 10:59:52 -05:00
migr-blocker.c Include qemu-common.h exactly where needed 2019-06-12 13:20:20 +02:00
module-opts.c qemu-config: load modules when instantiating option groups 2021-05-26 14:49:46 +02:00
monitor-core.c monitor: Make current monitor a per-coroutine property 2020-10-09 07:08:19 +02:00
monitor.c hmp: Fail gracefully if chardev is already in use 2020-03-06 17:21:28 +01:00
pci-bus.c stubs: add pci_create_simple 2020-07-06 17:01:11 +02:00
pci-host-piix.c hw/pci-host/piix: Move i440FX declarations to hw/pci-host/i440fx.h 2019-11-05 23:33:12 +01:00
qdev.c qapi/meson: Restrict qdev code to system-mode emulation 2021-02-08 14:43:55 +01:00
qemu-timer-notify-cb.c cpu-timers, icount: new modules 2020-10-05 16:41:22 +02:00
qmp-command-available.c remove preconfig state 2020-12-15 12:51:48 -05:00
qmp_memory_device.c qom/object: Move Object typedef to 'qemu/typedefs.h' 2020-06-10 12:09:36 -04:00
qtest.c cpu-timers, icount: new modules 2020-10-05 16:41:22 +02:00
ram-block.c util/vfio-helpers.c: Use ram_block_discard_disable() in qemu_vfio_open_pci() 2020-11-16 13:22:17 -05:00
ramfb.c Revert "hw/display/ramfb: initialize fw-config space with xres/ yres" 2020-05-18 15:42:34 +02:00
replay-tools.c replay: fix icount request when replaying clock access 2021-02-16 17:15:39 +01:00
replay.c replay: do not build if TCG is not available 2020-10-22 11:53:54 -04:00
runstate-check.c sysemu: Split sysemu/runstate.h off sysemu/sysemu.h 2019-08-16 13:37:36 +02:00
semihost.c Do not include sysemu/sysemu.h if it's not really necessary 2021-05-02 17:24:50 +02:00
sysbus.c stubs: Clean up includes 2016-02-04 17:01:04 +00:00
target-get-monitor-def.c Clean up includes some more 2016-03-22 22:20:16 +01:00
target-monitor-defs.c Clean up includes some more 2016-03-22 22:20:16 +01:00
trace-control.c trace: remove global 'uint16 dstate[]' array 2016-10-12 09:35:54 +02:00
usb-dev-stub.c hw/usb: Do not build USB subsystem if not required 2021-05-04 08:38:23 +02:00
uuid.c qapi: Restrict query-uuid command to machine code 2020-09-29 15:41:35 +02:00
virtio-gpu-udmabuf.c virtio-gpu: Add helpers to create and destroy dmabuf objects 2021-05-27 12:07:37 +02:00
vm-stop.c sysemu: Split sysemu/runstate.h off sysemu/sysemu.h 2019-08-16 13:37:36 +02:00
vmgenid.c qapi: Restrict query-vm-generation-id command to machine code 2020-09-29 15:41:35 +02:00
vmstate.c cpu: Move CPUClass::vmsd to SysemuCPUOps 2021-05-26 15:33:59 -07:00
win32-kbd-hook.c ui/win32-kbd-hook: handle AltGr in a hook procedure 2020-05-19 09:06:44 +02:00
xen-hw-stub.c stubs/xen-hw-stub: drop xenstore_store_pv_console_info stub 2020-11-16 11:07:53 +00:00