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[PULL 34/61] cpus: avoid pause_all_vcpus getting stuck due to race
From: |
Paolo Bonzini |
Subject: |
[PULL 34/61] cpus: avoid pause_all_vcpus getting stuck due to race |
Date: |
Mon, 16 Mar 2020 22:27:01 +0100 |
From: Longpeng <address@hidden>
We found an issue when repeat reboot in guest during migration, it cause the
migration thread never be waken up again.
<main loop> |<migration_thread>
|
LOCK BQL |
... |
main_loop_should_exit |
pause_all_vcpus |
1. set all cpus ->stop=true |
and then kick |
2. return if all cpus is paused |
(by '->stopped == true'), else|
3. qemu_cond_wait [BQL UNLOCK] |
|LOCK BQL
|...
|do_vm_stop
| pause_all_vcpus
| (A)set all cpus ->stop=true
| and then kick
| (B)return if all cpus is paused
| (by '->stopped == true'), else
| (C)qemu_cond_wait [BQL UNLOCK]
4. be waken up and LOCK BQL | (D)be waken up BUT wait for BQL
5. goto 2. |
(BQL is still LOCKed) |
resume_all_vcpus |
1. set all cpus ->stop=false |
and ->stopped=false |
... |
BQL UNLOCK | (E)LOCK BQL
| (F)goto B. [but stopped is false now!]
|Finally, sleep at step 3 forever.
resume_all_vcpus should notice this race, so we need to move the change
of runstate before pause_all_vcpus in do_vm_stop() and ignore the resume
request if runstate is not running.
Cc: Dr. David Alan Gilbert <address@hidden>
Cc: Richard Henderson <address@hidden>
Signed-off-by: Longpeng <address@hidden>
Suggested-by: Paolo Bonzini <address@hidden>
Message-Id: <address@hidden>
Signed-off-by: Paolo Bonzini <address@hidden>
---
cpus.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/cpus.c b/cpus.c
index b4f8b84..ef441bd 100644
--- a/cpus.c
+++ b/cpus.c
@@ -1026,9 +1026,9 @@ static int do_vm_stop(RunState state, bool send_stop)
int ret = 0;
if (runstate_is_running()) {
+ runstate_set(state);
cpu_disable_ticks();
pause_all_vcpus();
- runstate_set(state);
vm_state_notify(0, state);
if (send_stop) {
qapi_event_send_stop();
@@ -1899,6 +1899,10 @@ void resume_all_vcpus(void)
{
CPUState *cpu;
+ if (!runstate_is_running()) {
+ return;
+ }
+
qemu_clock_enable(QEMU_CLOCK_VIRTUAL, true);
CPU_FOREACH(cpu) {
cpu_resume(cpu);
--
1.8.3.1
- [PULL 28/61] ui/curses: Make control_characters[] array const, (continued)
- [PULL 28/61] ui/curses: Make control_characters[] array const, Paolo Bonzini, 2020/03/16
- [PULL 32/61] Use -isystem for linux-headers dir, Paolo Bonzini, 2020/03/16
- [PULL 29/61] ui/curses: Move arrays to .heap to save 74KiB of .bss, Paolo Bonzini, 2020/03/16
- [PULL 31/61] softmmu/vl.c: Handle '-cpu help' and '-device help' before 'no default machine', Paolo Bonzini, 2020/03/16
- [PULL 33/61] exec/rom_reset: Free rom data during inmigrate skip, Paolo Bonzini, 2020/03/16
- [PULL 36/61] lockable: add QemuRecMutex support, Paolo Bonzini, 2020/03/16
- [PULL 40/61] scripts/cocci: Patch to replace memory_region_init_{ram, readonly -> rom}, Paolo Bonzini, 2020/03/16
- [PULL 35/61] lockable: add lock guards, Paolo Bonzini, 2020/03/16
- [PULL 42/61] hw/display: Use memory_region_init_rom() with read-only regions, Paolo Bonzini, 2020/03/16
- [PULL 30/61] qemu-cpu-models.rst: Document -noTSX, mds-no, taa-no, and tsx-ctrl, Paolo Bonzini, 2020/03/16
- [PULL 34/61] cpus: avoid pause_all_vcpus getting stuck due to race,
Paolo Bonzini <=
- [PULL 37/61] memory: Correctly return alias region type, Paolo Bonzini, 2020/03/16
- [PULL 38/61] memory: Simplify memory_region_init_rom_nomigrate() to ease review, Paolo Bonzini, 2020/03/16
- [PULL 39/61] scripts/cocci: Rename memory-region-{init-ram -> housekeeping}, Paolo Bonzini, 2020/03/16
- [PULL 41/61] hw/arm: Use memory_region_init_rom() with read-only regions, Paolo Bonzini, 2020/03/16
- [PULL 44/61] hw/net: Use memory_region_init_rom() with read-only regions, Paolo Bonzini, 2020/03/16
- [PULL 45/61] hw/pci-host: Use memory_region_init_rom() with read-only regions, Paolo Bonzini, 2020/03/16
- [PULL 46/61] hw/ppc: Use memory_region_init_rom() with read-only regions, Paolo Bonzini, 2020/03/16
- [PULL 43/61] hw/m68k: Use memory_region_init_rom() with read-only regions, Paolo Bonzini, 2020/03/16
- [PULL 48/61] hw/sh4: Use memory_region_init_rom() with read-only regions, Paolo Bonzini, 2020/03/16
- [PULL 50/61] scripts/cocci: Patch to detect potential use of memory_region_init_rom, Paolo Bonzini, 2020/03/16