Re: [PATCH v2 4/4] migration: Check in savevm_state_handler_insert for dups

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Peter Xu (peterx@redhat.com) wrote:
> Before finally register one SaveStateEntry, we detect for duplicated
> entries.  This could be helpful to notify us asap instead of get
> silent migration failures which could be hard to diagnose.
> 
> For example, this patch will generate a message like this (if without
> previous fixes on x2apic) as long as we wants to boot a VM instance
> with "-smp 200,maxcpus=288,sockets=2,cores=72,threads=2" and QEMU will
> bail out even before VM starts:
> 
> savevm_state_handler_insert: Detected duplicate SaveStateEntry: id=apic, instance_id=0x0
> 
> Suggested-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> Signed-off-by: Peter Xu <peterx@redhat.com>

Right, lets see what this triggers :-)

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

> ---
>  migration/savevm.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/migration/savevm.c b/migration/savevm.c
> index 1e44f06d7a..83e91ddafa 100644
> --- a/migration/savevm.c
> +++ b/migration/savevm.c
> @@ -264,6 +264,8 @@ static SaveState savevm_state = {
>      .global_section_id = 0,
>  };
>  
> +static SaveStateEntry *find_se(const char *idstr, uint32_t instance_id);
> +
>  static bool should_validate_capability(int capability)
>  {
>      assert(capability >= 0 && capability < MIGRATION_CAPABILITY__MAX);
> @@ -714,6 +716,18 @@ static void savevm_state_handler_insert(SaveStateEntry *nse)
>  
>      assert(priority <= MIG_PRI_MAX);
>  
> +    /*
> +     * This should never happen otherwise migration will probably fail
> +     * silently somewhere because we can be wrongly applying one
> +     * object properties upon another one.  Bail out ASAP.
> +     */
> +    if (find_se(nse->idstr, nse->instance_id)) {
> +        error_report("%s: Detected duplicate SaveStateEntry: "
> +                     "id=%s, instance_id=0x%"PRIx32, __func__,
> +                     nse->idstr, nse->instance_id);
> +        exit(EXIT_FAILURE);
> +    }
> +
>      QTAILQ_FOREACH(se, &savevm_state.handlers, entry) {
>          if (save_state_priority(se) < priority) {
>              break;
> -- 
> 2.21.0
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK