[Qemu-devel] [PATCH] migration: Guard ram_bytes_remaining against early call

[Qemu-devel] [PATCH] migration: Guard ram_bytes_remaining against early call

[Dr. David Alan Gilbert (git)]

From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>

Calling ram_bytes_remaining during the early part of setup is unsafe
because the ram_state isn't yet initialised.

This can happen in the sequence:
   migrate
   migrate_cancel
   info migrate

if the migrate sticks trying to connect (e.g. to an unresponsive
destination due to the connect timeout).  Here 'info migrate' sees
a state of CANCELLING and so assumes the migrate has partially happened.

partial fix for:
RH bz: https://bugzilla.redhat.com/show_bug.cgi?id=1525899
Reported-by: Xianxian Wang <xianwang@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
 migration/ram.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/migration/ram.c b/migration/ram.c
index 021d583b9b..cb1950f3eb 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -237,7 +237,8 @@ static RAMState *ram_state;
 
 uint64_t ram_bytes_remaining(void)
 {
-    return ram_state->migration_dirty_pages * TARGET_PAGE_SIZE;
+    return ram_state ? (ram_state->migration_dirty_pages * TARGET_PAGE_SIZE) :
+                       0;
 }
 
 MigrationStats ram_counters;
-- 
2.14.3

Re: [Qemu-devel] [PATCH] migration: Guard ram_bytes_remaining against early call

[Peter Xu]

On Fri, Dec 15, 2017 at 11:51:23AM +0000, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> 
> Calling ram_bytes_remaining during the early part of setup is unsafe
> because the ram_state isn't yet initialised.
> 
> This can happen in the sequence:
>    migrate
>    migrate_cancel
>    info migrate
> 
> if the migrate sticks trying to connect (e.g. to an unresponsive
> destination due to the connect timeout).  Here 'info migrate' sees
> a state of CANCELLING and so assumes the migrate has partially happened.
> 
> partial fix for:
> RH bz: https://bugzilla.redhat.com/show_bug.cgi?id=1525899
> Reported-by: Xianxian Wang <xianwang@redhat.com>
> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

Reviewed-by: Peter Xu <peterx@redhat.com>

Now we fetch this as long as !COMPLETE:

    if (s->state != MIGRATION_STATUS_COMPLETED) {
        info->ram->remaining = ram_bytes_remaining();
        info->ram->dirty_pages_rate = ram_counters.dirty_pages_rate;
    }

Maybe we should also narrow this down some day.  Thanks,

-- 
Peter Xu

Re: [Qemu-devel] [PATCH] migration: Guard ram_bytes_remaining against early call

[Juan Quintela]

"Dr. David Alan Gilbert (git)" <dgilbert@redhat.com> wrote:
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
>
> Calling ram_bytes_remaining during the early part of setup is unsafe
> because the ram_state isn't yet initialised.
>
> This can happen in the sequence:
>    migrate
>    migrate_cancel
>    info migrate
>
> if the migrate sticks trying to connect (e.g. to an unresponsive
> destination due to the connect timeout).  Here 'info migrate' sees
> a state of CANCELLING and so assumes the migrate has partially happened.
>
> partial fix for:
> RH bz: https://bugzilla.redhat.com/show_bug.cgi?id=1525899
> Reported-by: Xianxian Wang <xianwang@redhat.com>
> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

Reviewed-by: Juan Quintela <quintela@redhat.com>