Hi Ming,
On Fri, Nov 12, 2021 at 1:47 PM Ming Lei <ming.lei@xxxxxxxxxx> wrote:
> On Fri, Nov 12, 2021 at 09:44:41AM +0100, Christoph Hellwig wrote:
> > On Fri, Nov 12, 2021 at 04:37:19PM +0800, Ming Lei wrote:
> > > > can only be used for reads, and no fua can be set if the preallocating
> > > > I/O didn't use fua, etc.
> > > >
> > > > What are the pitfalls of just chanigng cmd_flags?
> > >
> > > Then we need to check cmd_flags carefully, such as hctx->type has to
> > > be same, flush & passthrough flags has to be same, that said all
> > > ->cmd_flags used for allocating rqs have to be same with the following
> > > bio->bi_opf.
> > >
> > > In usual cases, I guess all IOs submitted from same plug batch should be
> > > same type. If not, we can switch to change cmd_flags.
> >
> > Jens: is this a limit fitting into your use cases?
> >
> > I guess as a quick fix this rejecting different flags is probably the
> > best we can do for now, but I suspect we'll want to eventually relax
> > them.
>
> rw mixed workload will be affected, so I think we need to switch to
> change cmd_flags, how about the following patch?
>
> From 9ab77b7adee768272944c20b7cffc8abdb85a35b Mon Sep 17 00:00:00 2001
> From: Ming Lei <ming.lei@xxxxxxxxxx>
> Date: Fri, 12 Nov 2021 08:14:38 +0800
> Subject: [PATCH] blk-mq: fix filesystem I/O request allocation
>
> submit_bio_checks() may update bio->bi_opf, so we have to initialize
> blk_mq_alloc_data.cmd_flags with bio->bi_opf after submit_bio_checks()
> returns when allocating new request.
>
> In case of using cached request, fallback to allocate new request if
> cached rq isn't compatible with the incoming bio, otherwise change
> rq->cmd_flags with incoming bio->bi_opf.
>
> Fixes: 900e080752025f00 ("block: move queue enter logic into blk_mq_submit_bio()")
> Reported-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
Thanks, this alternative patch seems to work fine, too.
Tested-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
