Re: [PATCH] blkdebug: ignore invalid rules in non-coroutine context

[Markus Armbruster <armbru@redhat.com>]

Paolo Bonzini <pbonzini@redhat.com> writes:

> blkdebug events can be called from either non-coroutine or coroutine
> contexts.  However, some actions (specifically suspend actions and
> errors reported with immediately=off) only make sense from within
> a coroutine.
>
> Currently, using those action would lead to an abort() in
> qemu_coroutine_yield() ("Co-routine is yielding to no one").
> Catch them and print an error instead.
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  block/blkdebug.c | 17 ++++++++++++++---
>  1 file changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/block/blkdebug.c b/block/blkdebug.c
> index bbf2948703..bf0aedb17d 100644
> --- a/block/blkdebug.c
> +++ b/block/blkdebug.c
> @@ -31,6 +31,7 @@
>  #include "block/qdict.h"
>  #include "qemu/module.h"
>  #include "qemu/option.h"
> +#include "qemu/error-report.h"
>  #include "qapi/qapi-visit-block-core.h"
>  #include "qapi/qmp/qdict.h"
>  #include "qapi/qmp/qlist.h"
> @@ -623,8 +624,13 @@ static int rule_check(BlockDriverState *bs, uint64_t offset, uint64_t bytes,
>  
>      qemu_mutex_unlock(&s->lock);
>      if (!immediately) {
> -        aio_co_schedule(qemu_get_current_aio_context(), qemu_coroutine_self());
> -        qemu_coroutine_yield();
> +        if (qemu_in_coroutine()) {
> +            aio_co_schedule(qemu_get_current_aio_context(), qemu_coroutine_self());
> +            qemu_coroutine_yield();
> +        } else {
> +            error_report("Non-coroutine event %s needs immediately = off\n",
> +                         BlkdebugEvent_lookup.array[rule->event]);

rule_check() is called from blkdebug_co_preadv(), blkdebug_co_pwritev(),
blkdebug_co_pwrite_zeroes(), blkdebug_co_pdiscard(),
blkdebug_co_block_status() (all marked coroutine_fn), and
blkdebug_co_flush() (which looks like it should be marked coroutine_fn).

Ignorant question: how could it be called outside coroutine context?

Also, code smell: reporting an error without taking an error path.  But
let's worry about that only after I understand the problem you're trying
to fix.

> +        }
>      }
>  
>      return -error;
> @@ -858,7 +864,12 @@ static void blkdebug_debug_event(BlockDriverState *bs, BlkdebugEvent event)
>      }
>  
>      while (actions_count[ACTION_SUSPEND] > 0) {
> -        qemu_coroutine_yield();
> +        if (qemu_in_coroutine()) {
> +            qemu_coroutine_yield();
> +        } else {
> +            error_report("Non-coroutine event %s cannot suspend\n",
> +                         BlkdebugEvent_lookup.array[event]);
> +        }
>          actions_count[ACTION_SUSPEND]--;
>      }
>  }