Re: [PATCH v3 1/5] blkdebug: refactor removal of a suspended request

[Vladimir Sementsov-Ogievskiy]

17.05.2021 17:50, Emanuele Giuseppe Esposito wrote:
> Extract to a separate function.  Do not rely on FOREACH_SAFE, which is
> only "safe" if the *current* node is removed---not if another node is
> removed.  Instead, just walk the entire list from the beginning when
> asked to resume all suspended requests with a given tag.
>
> Co-developed-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
> ---
>   block/blkdebug.c | 28 +++++++++++++++++-----------
>   1 file changed, 17 insertions(+), 11 deletions(-)
>
> diff --git a/block/blkdebug.c b/block/blkdebug.c
> index 2c0b9b0ee8..8f19d991fa 100644
> --- a/block/blkdebug.c
> +++ b/block/blkdebug.c
> @@ -793,7 +793,6 @@ static void suspend_request(BlockDriverState *bs, 
> BlkdebugRule *rule)
>           printf("blkdebug: Resuming request '%s'\n", r.tag);
>       }
>   
> -    QLIST_REMOVE(&r, next);
>       g_free(r.tag);
>   }
>   
> @@ -869,25 +868,35 @@ static int blkdebug_debug_breakpoint(BlockDriverState *bs, const char *event,
>       return 0;
>   }
>   
> -static int blkdebug_debug_resume(BlockDriverState *bs, const char *tag)
> +static int resume_req_by_tag(BDRVBlkdebugState *s, const char *tag, bool all)
>   {
> -    BDRVBlkdebugState *s = bs->opaque;
> -    BlkdebugSuspendedReq *r, *next;
> +    BlkdebugSuspendedReq *r;
>   
> -    QLIST_FOREACH_SAFE(r, &s->suspended_reqs, next, next) {
> +retry:
> +    QLIST_FOREACH(r, &s->suspended_reqs, next) {
>           if (!strcmp(r->tag, tag)) {
> +            QLIST_REMOVE(r, next);
>               qemu_coroutine_enter(r->co);
> +            if (all) {
> +                goto retry;
> +            }
>               return 0;
>           }
>       }
>       return -ENOENT;
>   }
>   
> +static int blkdebug_debug_resume(BlockDriverState *bs, const char *tag)
> +{
> +    BDRVBlkdebugState *s = bs->opaque;
> +
> +    return resume_req_by_tag(s, tag, false);
> +}
> +
>   static int blkdebug_debug_remove_breakpoint(BlockDriverState *bs,
>                                               const char *tag)
>   {
>       BDRVBlkdebugState *s = bs->opaque;
> -    BlkdebugSuspendedReq *r, *r_next;
>       BlkdebugRule *rule, *next;
>       int i, ret = -ENOENT;
>   
> @@ -900,11 +909,8 @@ static int blkdebug_debug_remove_breakpoint(BlockDriverState *bs,
>               }
>           }
>       }
> -    QLIST_FOREACH_SAFE(r, &s->suspended_reqs, next, r_next) {
> -        if (!strcmp(r->tag, tag)) {
> -            qemu_coroutine_enter(r->co);
> -            ret = 0;
> -        }
> +    if (resume_req_by_tag(s, tag, true) == 0) {
> +        ret = 0;
>       }
>       return ret;
>   }

Interesting, could we really have several suspended_reqs with same tag, keeping 
in mind suspend_requests() removes rule before creating suspended_req with same 
tag.. Probably user could create new rule with same tag, when existing requests 
is suspended? Not sure is such behavior expected or should be abandoned. Still, 
it's all not about that patch:

Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>


--
Best regards,
Vladimir