Le Friday 17 Jan 2014 à 15:15:09 (+0100), Kevin Wolf a écrit :
> We can only have a single wait_serialising_requests() call per request
> because otherwise we can run into deadlocks where requests are waiting
> for each other. The same is true when wait_serialising_requests() is not
> at the very beginning of a request, so that other requests can be issued
> between the start of the tracking and wait_serialising_requests().
>
> Fix this by changing wait_serialising_requests() to ignore requests that
> are already (directly or indirectly) waiting for the calling request.
>
> Signed-off-by: Kevin Wolf <kw...@redhat.com>
> Reviewed-by: Max Reitz <mre...@redhat.com>
> ---
> block.c | 13 ++++++++++---
> include/block/block_int.h | 2 ++
> 2 files changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/block.c b/block.c
> index e72966a..55e8c69 100644
> --- a/block.c
> +++ b/block.c
> @@ -2148,9 +2148,16 @@ static void coroutine_fn
> wait_serialising_requests(BdrvTrackedRequest *self)
> */
> assert(qemu_coroutine_self() != req->co);
>
> - qemu_co_queue_wait(&req->wait_queue);
> - retry = true;
> - break;
> + /* If the request is already (indirectly) waiting for us, or
> + * will wait for us as soon as it wakes up, then just go on
> + * (instead of producing a deadlock in the former case). */
> + if (!req->waiting_for) {
> + self->waiting_for = req;
> + qemu_co_queue_wait(&req->wait_queue);
> + self->waiting_for = NULL;
> + retry = true;
> + break;
> + }
> }
> }
> } while (retry);
> diff --git a/include/block/block_int.h b/include/block/block_int.h
> index ccd2c68..fdf0e0b 100644
> --- a/include/block/block_int.h
> +++ b/include/block/block_int.h
> @@ -68,6 +68,8 @@ typedef struct BdrvTrackedRequest {
> QLIST_ENTRY(BdrvTrackedRequest) list;
> Coroutine *co; /* owner, used for deadlock detection */
> CoQueue wait_queue; /* coroutines blocked on this request */
> +
> + struct BdrvTrackedRequest *waiting_for;
> } BdrvTrackedRequest;
>
> struct BlockDriver {
> --
> 1.8.1.4
>
>
Reviewed-by: Benoit Canet <ben...@irqsave.net>
