On 11/16/21 14:54, Peter Xu wrote:
> When finalizing the dump-guest-memory with detached mode, we'll first set dump
> status to either FAIL or COMPLETE before doing the cleanup, however right
> after
> the dump status change it's possible that another dump-guest-memory qmp
> command
> is sent so both the main thread and dump thread (which is during cleanup)
> could
> be accessing dump state in parallel. That's racy.
>
> Fix it by protecting the finalizing phase of dump-guest-memory using BQL as
> well, as qmp_dump_guest_memory() (which is the QEMU main thread) requires BQL.
> To do that, we expand the BQL from dump_cleanup() into dump_process(), so we
> will take the BQL longer than before. The critical section must cover the
> status switch from ACTIVE->{FAIL|COMPLETE} so as to make sure there's no race
> any more.
>
> We can also just introduce a specific mutex to serialize the dump process, but
> BQL should be enough for now so far, not to mention vm_start() in dump_cleanup
> will need BQL anyway, so maybe easier to just use the same mutex.
>
> Reported-by: Laszlo Ersek <ler...@redhat.com>
> Reviewed-by: Marc-André Lureau <marcandre.lur...@redhat.com>
> Signed-off-by: Peter Xu <pet...@redhat.com>
> ---
> v2:
> - Fix parallel spelling [Marc-Andre]
> - Add r-b for Marc-Andre
> - Mention that qmp_dump_guest_memory() is with BQL held [Laszlo]
> ---
> dump/dump.c | 24 ++++++++++++++++++------
> 1 file changed, 18 insertions(+), 6 deletions(-)
Reviewed-by: Laszlo Ersek <ler...@redhat.com>
Thank you!
Laszlo
