On Tue, Jul 25, 2023 at 09:00:59PM +0800, chengming.zhou@xxxxxxxxx wrote:
> From: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
>
> The cmd_flags in blk_kick_flush() should inherit the original request's
> cmd_flags, but the current code looks buggy to me:
Should it? I know the code is kinda trying to do it, but does it really
make sense? Adding Hannes who originally added this inheritance and
discussing the details below:
> flush_rq->cmd_flags = REQ_OP_FLUSH | REQ_PREFLUSH;
> - flush_rq->cmd_flags |= (flags & REQ_DRV) | (flags & REQ_FAILFAST_MASK);
> + flush_rq->cmd_flags |= (first_rq->cmd_flags & REQ_DRV) |
> + (first_rq->cmd_flags & REQ_FAILFAST_MASK);
Two cases here:
1) REQ_FAILFAST_MASK: I don't think this is actually set on flush request
currently, and even if it was applying it to the flush that serves more
than a single originating command seems wrong to me.
2) REQ_DRV is only set by drivers that have seen a bio. For dm this
is used as REQ_DM_POLL_LIST which should never be set for a flush/fua
request. For nvme-mpath it is REQ_NVME_MPATH, which is set in the
bio based driver and used for decision making in the I/O completion
handler. So I guess this one actually does need to get passed
through.
