25.03.2019, 14:58, "Juan Quintela" <quint...@redhat.com>:
> Yury Kotov <yury-ko...@yandex-team.ru> wrote:
>> I found a bug in QEMU 2.12 with adding memory-backend while live migration
>> thread is running.
>>
>> But it seems that this bug was implicitly fixed in this commit (QEMU 3.0):
>> b895de50: migration: discard non-migratable RAMBlocks
>>
>> I think it's better to disallow add/del memory backends during migration to
>> to prevent other possible problems. Anyway, user can't use this memory
>> because
>> of disabled hotplug/hotunplug devs.
>
> Hi
>
> My understanding is that we already disable memory hotplug/unplug during
> migration. At least, the idea of those patches was to disable all
> hotplug/unplug during migration. The only reason that I can think for
> using this patch is if anyone is planning about support some
> hotplug/upplug during migration (to my knowledge, nobody is working on
> that).
>
Sorry, what patches do you mean? It seems that I missed them...
> So, I think it is better to just disallow on high level all hoplug
> operations, instead of in all backends.
>
Agreed. I also had such idea and I did a quick look on this, but din't found how
to do it without some refactoring.
> But will wait to see what everybody else think about it.
>
> BTW, if we plan to ship this for an old qemu, I will try to disable
> hotplug for all devices, not only memory, no?
>
> Later, Juan.
>
>> The idea of this commit is the same as that:
>> b06424de: migration: Disable hotplug/unplug memory during migration
>>
>> Backtrace of this bug in QEMU 2.12:
>> 0 find_next_bit (addr=addr@entry=0x0, size=size@entry=262144,
>> offset=offset@entry=0) at util/bitops.c:46
>> 1 migration_bitmap_find_dirty (rs=0x7f58f80008c0, start=0,
>> rb=0x5557e66e3200) at migration/ram.c:816
>> 2 find_dirty_block (again=<synthetic pointer>, pss=<synthetic pointer>,
>> rs=0x7f58f80008c0) at migration/ram.c:1243
>> 3 ram_find_and_save_block (rs=rs@entry=0x7f58f80008c0,
>> last_stage=last_stage@entry=false) at migration/ram.c:1592
>> 4 ram_find_and_save_block (last_stage=false, rs=0x7f58f80008c0) at
>> migration/ram.c:2335
>> 5 ram_save_iterate (f=0x5557e69f1000, opaque=<optimized out>) at
>> migration/ram.c:2338
>> 6 qemu_savevm_state_iterate (f=0x5557e69f1000, postcopy=false) at
>> migration/savevm.c:1191
>> 7 migration_iteration_run (s=0x5557e666b030) at migration/migration.c:2301
>> 8 migration_thread (opaque=0x5557e666b030) at migration/migration.c:2409
>> 9 start_thread (arg=0x7f59055d5700) at pthread_create.c:333
>> 10 clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109
>>
>> Signed-off-by: Yury Kotov <yury-ko...@yandex-team.ru>
>> ---
>> backends/hostmem.c | 9 ++++++++-
>> 1 file changed, 8 insertions(+), 1 deletion(-)
>>
>> diff --git a/backends/hostmem.c b/backends/hostmem.c
>> index f61093654e..5c71bd3f6b 100644
>> --- a/backends/hostmem.c
>> +++ b/backends/hostmem.c
>> @@ -18,6 +18,7 @@
>> #include "qapi/visitor.h"
>> #include "qemu/config-file.h"
>> #include "qom/object_interfaces.h"
>> +#include "migration/misc.h"
>>
>> #ifdef CONFIG_NUMA
>> #include <numaif.h>
>> @@ -271,6 +272,11 @@ host_memory_backend_memory_complete(UserCreatable *uc,
>> Error **errp)
>> void *ptr;
>> uint64_t sz;
>>
>> + if (!migration_is_idle()) {
>> + error_setg(errp, "Adding memory-backend isn't allowed while migrating");
>> + goto out;
>> + }
>> +
>> if (bc->alloc) {
>> bc->alloc(backend, &local_err);
>> if (local_err) {
>> @@ -344,7 +350,8 @@ out:
>> static bool
>> host_memory_backend_can_be_deleted(UserCreatable *uc)
>> {
>> - if (host_memory_backend_is_mapped(MEMORY_BACKEND(uc))) {
>> + if (host_memory_backend_is_mapped(MEMORY_BACKEND(uc)) ||
>> + !migration_is_idle()) {
>> return false;
>> } else {
>> return true;
Regards,
Yury
