linux-kernel - Re: [v4 PATCH] block: introduce block_rq

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Message-ID: <CAHbLzkoaM=e7EXpKQkxP+BRi-1gSjfJ=9GHM+s=5Lyh2ksZ+Kw@mail.gmail.com>
Date:   Wed, 26 Jan 2022 10:35:59 -0800
From:   Yang Shi <shy828301@...il.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Jens Axboe <axboe@...nel.dk>, Steven Rostedt <rostedt@...dmis.org>,
        Cong Wang <xiyou.wangcong@...il.com>,
        linux-block@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [v4 PATCH] block: introduce block_rq_error tracepoint

On Wed, Jan 26, 2022 at 12:21 AM Christoph Hellwig <hch@...radead.org> wrote:
>
> On Tue, Jan 25, 2022 at 12:35:48PM -0800, Yang Shi wrote:
> > Currently, rasdaemon uses the existing tracepoint block_rq_complete
> > and filters out non-error cases in order to capture block disk errors.
> >
> > But there are a few problems with this approach:
> >
> > 1. Even kernel trace filter could do the filtering work, there is
> >    still some overhead after we enable this tracepoint.
> >
> > 2. The filter is merely based on errno, which does not align with kernel
> >    logic to check the errors for print_req_error().
> >
> > 3. block_rq_complete only provides dev major and minor to identify
> >    the block device, it is not convenient to use in user-space.
> >
> > So introduce a new tracepoint block_rq_error just for the error case
> > and provides the device name for convenience too. With this patch,
> > rasdaemon could switch to block_rq_error.
> >
> > Cc: Jens Axboe <axboe@...nel.dk>
> > Reviewed-by: Steven Rostedt <rostedt@...dmis.org>
> > Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
> > Signed-off-by: Yang Shi <shy828301@...il.com>
> > ---
> > The v3 patch was submitted in Feb 2020, and Steven reviewed the patch, but
> > it was not merged to upstream. See
> > https://lore.kernel.org/lkml/20200203053650.8923-1-xiyou.wangcong@gmail.com/.
> >
> > The problems fixed by that patch still exist and we do need it to make
> > disk error handling in rasdaemon easier. So this resurrected it and
> > continued the version number.
> >
> > v3 --> v4:
> >  * Rebased to v5.17-rc1.
> >  * Collected reviewed-by tag from Steven.
> >
> >  block/blk-mq.c               |  4 +++-
> >  include/trace/events/block.h | 41 ++++++++++++++++++++++++++++++++++++
> >  2 files changed, 44 insertions(+), 1 deletion(-)
> >
> > diff --git a/block/blk-mq.c b/block/blk-mq.c
> > index f3bf3358a3bb..bb0593f93675 100644
> > --- a/block/blk-mq.c
> > +++ b/block/blk-mq.c
> > @@ -789,8 +789,10 @@ bool blk_update_request(struct request *req, blk_status_t error,
> >  #endif
> >
> >       if (unlikely(error && !blk_rq_is_passthrough(req) &&
> > -                  !(req->rq_flags & RQF_QUIET)))
> > +                  !(req->rq_flags & RQF_QUIET))) {
> > +             trace_block_rq_error(req, blk_status_to_errno(error), nr_bytes);
>
> Please report the atual block layer status code instead of the errno
> mapping here.

Sure, thanks.