Am 18.12.2019 um 14:17 hat Paolo Bonzini geschrieben:
> Marking without waiting would not result in actual serialising behavior.
> Thus, make a call bdrv_mark_request_serialising sufficient for
> serialisation to happen.
>
> Signed-off-by: Paolo Bonzini <[email protected]>
> @@ -1851,13 +1841,18 @@ bdrv_co_write_req_prepare(BdrvChild *child, int64_t
> offset, uint64_t bytes,
> assert(!(flags & ~BDRV_REQ_MASK));
>
> if (flags & BDRV_REQ_SERIALISING) {
> - bdrv_mark_request_serialising(req, bdrv_get_cluster_size(bs));
> + waited = bdrv_mark_request_serialising(req,
> bdrv_get_cluster_size(bs));
> + /*
> + * For a misaligned request, we should have already waited
> + * in bdrv_padding_rmw_read and locked out concurrent writers.
Actually, bdrv_padding_rmw_read() only asserts that the request is
already serialised. bdrv_mark_request_serialising() is already called by
the callers of bdrv_padding_rmw_read().
> + */
> + assert(!waited ||
> + (req->offset == req->overlap_offset &&
> + req->bytes == req->overlap_bytes));
> + } else {
> + bdrv_wait_serialising_requests(req);
> }
>
> - waited = bdrv_wait_serialising_requests(req);
> -
> - assert(!waited || !req->serialising ||
> - is_request_serialising_and_aligned(req));
> assert(req->overlap_offset <= offset);
> assert(offset + bytes <= req->overlap_offset + req->overlap_bytes);
> assert(end_sector <= bs->total_sectors || child->perm & BLK_PERM_RESIZE);
Other than the comment, the patch looks fine to me.
Kevin
