RE: [PATCH v4 07/10] migration: split migration_incoming_co
> -Original Message- > From: Vladimir Sementsov-Ogievskiy > Sent: Thursday, May 4, 2023 6:52 AM > To: Peter Xu > Cc: qemu-devel@nongnu.org; lukasstra...@web.de; quint...@redhat.com; > Zhang, Chen ; Zhang, Hailiang > ; Leonardo Bras > Subject: Re: [PATCH v4 07/10] migration: split migration_incoming_co > > On 02.05.23 23:48, Peter Xu wrote: > > On Fri, Apr 28, 2023 at 10:49:25PM +0300, Vladimir Sementsov-Ogievskiy > wrote: > >> Originally, migration_incoming_co was introduced by > >> 25d0c16f625feb3b6 > >> "migration: Switch to COLO process after finishing loadvm" > >> to be able to enter from COLO code to one specific yield point, added > >> by 25d0c16f625feb3b6. > >> > >> Later in 923709896b1b0 > >> "migration: poll the cm event for destination qemu" > >> we reused this variable to wake the migration incoming coroutine from > >> RDMA code. > >> > >> That was doubtful idea. Entering coroutines is a very fragile thing: > >> you should be absolutely sure which yield point you are going to enter. > >> > >> I don't know how much is it safe to enter during qemu_loadvm_state() > >> which I think what RDMA want to do. But for sure RDMA shouldn't enter > >> the special COLO-related yield-point. As well, COLO code doesn't want > >> to enter during qemu_loadvm_state(), it want to enter it's own > >> specific yield-point. > >> > >> As well, when in 8e48ac95865ac97d > >> "COLO: Add block replication into colo process" we added > >> bdrv_invalidate_cache_all() call (now it's called activate_all()) it > >> became possible to enter the migration incoming coroutine during that > >> call which is wrong too. > >> > >> So, let't make these things separate and disjoint: loadvm_co for > >> RDMA, non-NULL during qemu_loadvm_state(), and colo_incoming_co for > >> COLO, non-NULL only around specific yield. > >> > >> Signed-off-by: Vladimir Sementsov-Ogievskiy > >> > >> --- > >> migration/colo.c | 4 ++-- > >> migration/migration.c | 8 ++-- > >> migration/migration.h | 9 - > >> 3 files changed, 16 insertions(+), 5 deletions(-) > > > > The idea looks right to me, but I really know mostly nothing on > > coroutines and also rdma+colo.. > > > > Is the other ref in rdma.c (rdma_cm_poll_handler()) still missing? > > > > Oops right.. I was building with rdma disabled. Will fix. > > Thanks a lot for reviewing! > Yes, I know some people and company try to enable COLO with RDMA. But in my side, I haven't tried this way yet. Thanks Chen > -- > Best regards, > Vladimir
Re: [PATCH v4 07/10] migration: split migration_incoming_co
On 02.05.23 23:48, Peter Xu wrote: On Fri, Apr 28, 2023 at 10:49:25PM +0300, Vladimir Sementsov-Ogievskiy wrote: Originally, migration_incoming_co was introduced by 25d0c16f625feb3b6 "migration: Switch to COLO process after finishing loadvm" to be able to enter from COLO code to one specific yield point, added by 25d0c16f625feb3b6. Later in 923709896b1b0 "migration: poll the cm event for destination qemu" we reused this variable to wake the migration incoming coroutine from RDMA code. That was doubtful idea. Entering coroutines is a very fragile thing: you should be absolutely sure which yield point you are going to enter. I don't know how much is it safe to enter during qemu_loadvm_state() which I think what RDMA want to do. But for sure RDMA shouldn't enter the special COLO-related yield-point. As well, COLO code doesn't want to enter during qemu_loadvm_state(), it want to enter it's own specific yield-point. As well, when in 8e48ac95865ac97d "COLO: Add block replication into colo process" we added bdrv_invalidate_cache_all() call (now it's called activate_all()) it became possible to enter the migration incoming coroutine during that call which is wrong too. So, let't make these things separate and disjoint: loadvm_co for RDMA, non-NULL during qemu_loadvm_state(), and colo_incoming_co for COLO, non-NULL only around specific yield. Signed-off-by: Vladimir Sementsov-Ogievskiy --- migration/colo.c | 4 ++-- migration/migration.c | 8 ++-- migration/migration.h | 9 - 3 files changed, 16 insertions(+), 5 deletions(-) The idea looks right to me, but I really know mostly nothing on coroutines and also rdma+colo.. Is the other ref in rdma.c (rdma_cm_poll_handler()) still missing? Oops right.. I was building with rdma disabled. Will fix. Thanks a lot for reviewing! -- Best regards, Vladimir
Re: [PATCH v4 07/10] migration: split migration_incoming_co
On Fri, Apr 28, 2023 at 10:49:25PM +0300, Vladimir Sementsov-Ogievskiy wrote: > Originally, migration_incoming_co was introduced by > 25d0c16f625feb3b6 >"migration: Switch to COLO process after finishing loadvm" > to be able to enter from COLO code to one specific yield point, added > by 25d0c16f625feb3b6. > > Later in 923709896b1b0 > "migration: poll the cm event for destination qemu" > we reused this variable to wake the migration incoming coroutine from > RDMA code. > > That was doubtful idea. Entering coroutines is a very fragile thing: > you should be absolutely sure which yield point you are going to enter. > > I don't know how much is it safe to enter during qemu_loadvm_state() > which I think what RDMA want to do. But for sure RDMA shouldn't enter > the special COLO-related yield-point. As well, COLO code doesn't want > to enter during qemu_loadvm_state(), it want to enter it's own specific > yield-point. > > As well, when in 8e48ac95865ac97d > "COLO: Add block replication into colo process" we added > bdrv_invalidate_cache_all() call (now it's called activate_all()) > it became possible to enter the migration incoming coroutine during > that call which is wrong too. > > So, let't make these things separate and disjoint: loadvm_co for RDMA, > non-NULL during qemu_loadvm_state(), and colo_incoming_co for COLO, > non-NULL only around specific yield. > > Signed-off-by: Vladimir Sementsov-Ogievskiy > --- > migration/colo.c | 4 ++-- > migration/migration.c | 8 ++-- > migration/migration.h | 9 - > 3 files changed, 16 insertions(+), 5 deletions(-) The idea looks right to me, but I really know mostly nothing on coroutines and also rdma+colo.. Is the other ref in rdma.c (rdma_cm_poll_handler()) still missing? -- Peter Xu
[PATCH v4 07/10] migration: split migration_incoming_co
Originally, migration_incoming_co was introduced by
25d0c16f625feb3b6
"migration: Switch to COLO process after finishing loadvm"
to be able to enter from COLO code to one specific yield point, added
by 25d0c16f625feb3b6.
Later in 923709896b1b0
"migration: poll the cm event for destination qemu"
we reused this variable to wake the migration incoming coroutine from
RDMA code.
That was doubtful idea. Entering coroutines is a very fragile thing:
you should be absolutely sure which yield point you are going to enter.
I don't know how much is it safe to enter during qemu_loadvm_state()
which I think what RDMA want to do. But for sure RDMA shouldn't enter
the special COLO-related yield-point. As well, COLO code doesn't want
to enter during qemu_loadvm_state(), it want to enter it's own specific
yield-point.
As well, when in 8e48ac95865ac97d
"COLO: Add block replication into colo process" we added
bdrv_invalidate_cache_all() call (now it's called activate_all())
it became possible to enter the migration incoming coroutine during
that call which is wrong too.
So, let't make these things separate and disjoint: loadvm_co for RDMA,
non-NULL during qemu_loadvm_state(), and colo_incoming_co for COLO,
non-NULL only around specific yield.
Signed-off-by: Vladimir Sementsov-Ogievskiy
---
migration/colo.c | 4 ++--
migration/migration.c | 8 ++--
migration/migration.h | 9 -
3 files changed, 16 insertions(+), 5 deletions(-)
diff --git a/migration/colo.c b/migration/colo.c
index 6c7c313956..a688ac553a 100644
--- a/migration/colo.c
+++ b/migration/colo.c
@@ -145,8 +145,8 @@ static void secondary_vm_do_failover(void)
qemu_sem_post(>colo_incoming_sem);
/* For Secondary VM, jump to incoming co */
-if (mis->migration_incoming_co) {
-qemu_coroutine_enter(mis->migration_incoming_co);
+if (mis->colo_incoming_co) {
+qemu_coroutine_enter(mis->colo_incoming_co);
}
}
diff --git a/migration/migration.c b/migration/migration.c
index 8db0892317..23b2d187de 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -505,12 +505,14 @@ process_incoming_migration_co(void *opaque)
Error *local_err = NULL;
assert(mis->from_src_file);
-mis->migration_incoming_co = qemu_coroutine_self();
mis->largest_page_size = qemu_ram_pagesize_largest();
postcopy_state_set(POSTCOPY_INCOMING_NONE);
migrate_set_state(>state, MIGRATION_STATUS_NONE,
MIGRATION_STATUS_ACTIVE);
+
+mis->loadvm_co = qemu_coroutine_self();
ret = qemu_loadvm_state(mis->from_src_file);
+mis->loadvm_co = NULL;
ps = postcopy_state_get();
trace_process_incoming_migration_co_end(ret, ps);
@@ -551,7 +553,10 @@ process_incoming_migration_co(void *opaque)
qemu_thread_create(_incoming_thread, "COLO incoming",
colo_process_incoming_thread, mis, QEMU_THREAD_JOINABLE);
+
+mis->colo_incoming_co = qemu_coroutine_self();
qemu_coroutine_yield();
+mis->colo_incoming_co = NULL;
qemu_mutex_unlock_iothread();
/* Wait checkpoint incoming thread exit before free resource */
@@ -563,7 +568,6 @@ process_incoming_migration_co(void *opaque)
mis->bh = qemu_bh_new(process_incoming_migration_bh, mis);
qemu_bh_schedule(mis->bh);
-mis->migration_incoming_co = NULL;
return;
fail:
local_err = NULL;
diff --git a/migration/migration.h b/migration/migration.h
index 7721c7658b..48a46123a0 100644
--- a/migration/migration.h
+++ b/migration/migration.h
@@ -162,8 +162,15 @@ struct MigrationIncomingState {
int state;
+/*
+ * The incoming migration coroutine, non-NULL during qemu_loadvm_state().
+ * Used to wake the migration incoming coroutine from rdma code. How much
is
+ * it safe - it's a question.
+ */
+Coroutine *loadvm_co;
+
/* The coroutine we should enter (back) after failover */
-Coroutine *migration_incoming_co;
+Coroutine *colo_incoming_co;
QemuSemaphore colo_incoming_sem;
/*
--
2.34.1
