Hi

On Tue, Aug 24, 2021 at 7:27 PM Peter Xu <peterx@redhat.com> wrote:

> Both dump-guest-memory and live migration caches vm state at the beginning.
> Either of them entering the other one will cause race on the vm state, and
> even
> more severe on that (please refer to the crash report in the bug link).
>
> Let's block live migration in dump-guest-memory, and that'll also block
> dump-guest-memory if it detected that we're during a live migration.
>
> Side note: migrate_del_blocker() can be called even if the blocker is not
> inserted yet, so it's safe to unconditionally delete that blocker in
> dump_cleanup (g_slist_remove allows no-entry-found case).
>
> Suggested-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1996609
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>  dump/dump.c           | 20 +++++++++++++++-----
>  include/sysemu/dump.h |  1 +
>  2 files changed, 16 insertions(+), 5 deletions(-)
>
> diff --git a/dump/dump.c b/dump/dump.c
> index ab625909f3..7996d7a6c5 100644
> --- a/dump/dump.c
> +++ b/dump/dump.c
> @@ -29,6 +29,7 @@
>  #include "qemu/error-report.h"
>  #include "qemu/main-loop.h"
>  #include "hw/misc/vmcoreinfo.h"
> +#include "migration/blocker.h"
>
>  #ifdef TARGET_X86_64
>  #include "win_dump.h"
> @@ -101,6 +102,7 @@ static int dump_cleanup(DumpState *s)
>              qemu_mutex_unlock_iothread();
>          }
>      }
> +    migrate_del_blocker(s->dump_migration_blocker);
>
>      return 0;
>  }
> @@ -1857,6 +1859,19 @@ static void dump_init(DumpState *s, int fd, bool
> has_format,
>          }
>      }
>
> +    if (!s->dump_migration_blocker) {
> +        error_setg(&s->dump_migration_blocker,
> +                   "Live migration disabled: dump-guest-memory in
> progress");
> +    }
> +
> +    /*
> +     * Allows even for -only-migratable, but forbid migration during the
> +     * process of dump guest memory.
> +     */
> +    if (migrate_add_blocker_internal(s->dump_migration_blocker, errp)) {
> +        goto cleanup;
> +    }
> +
>

Shouldn't this be placed earlier in the function, before
runstate_is_running() and vm_stop() ?

     return;
>
>  cleanup:
> @@ -1927,11 +1942,6 @@ void qmp_dump_guest_memory(bool paging, const char
> *file,
>      Error *local_err = NULL;
>      bool detach_p = false;
>
> -    if (runstate_check(RUN_STATE_INMIGRATE)) {
> -        error_setg(errp, "Dump not allowed during incoming migration.");
> -        return;
> -    }
> -
>      /* if there is a dump in background, we should wait until the dump
>       * finished */
>      if (dump_in_progress()) {
> diff --git a/include/sysemu/dump.h b/include/sysemu/dump.h
> index 250143cb5a..7b619c2a43 100644
> --- a/include/sysemu/dump.h
> +++ b/include/sysemu/dump.h
> @@ -195,6 +195,7 @@ typedef struct DumpState {
>                                    * finished. */
>      uint8_t *guest_note;         /* ELF note content */
>      size_t guest_note_size;
> +    Error *dump_migration_blocker; /* Blocker for live migration */
>  } DumpState;
>
>  uint16_t cpu_to_dump16(DumpState *s, uint16_t val);
> --
> 2.31.1
>
>