io-uring.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Keith Busch <kbusch@kernel.org>
To: Jens Axboe <axboe@kernel.dk>
Cc: io-uring@vger.kernel.org, linux-block@vger.kernel.org, hch@infradead.org
Subject: Re: [PATCH 4/6] block: clear BIO_PERCPU_CACHE flag if polling isn't supported
Date: Fri, 13 Aug 2021 13:31:38 -0700	[thread overview]
Message-ID: <20210813203138.GA2761@dhcp-10-100-145-180.wdc.com> (raw)
In-Reply-To: <33d05811-a9c6-c1d3-8b9c-7b95bdadd457@kernel.dk>

On Fri, Aug 13, 2021 at 02:19:11PM -0600, Jens Axboe wrote:
> On 8/13/21 2:17 PM, Keith Busch wrote:
> > On Thu, Aug 12, 2021 at 11:41:58AM -0600, Jens Axboe wrote:
> >> Indeed. Wonder if we should make that a small helper, as any clear of
> >> REQ_HIPRI should clear BIO_PERCPU_CACHE as well.
> >>
> >>
> >> diff --git a/block/blk-core.c b/block/blk-core.c
> >> index 7e852242f4cc..d2722ecd4d9b 100644
> >> --- a/block/blk-core.c
> >> +++ b/block/blk-core.c
> >> @@ -821,11 +821,8 @@ static noinline_for_stack bool submit_bio_checks(struct bio *bio)
> >>  		}
> >>  	}
> >>  
> >> -	if (!test_bit(QUEUE_FLAG_POLL, &q->queue_flags)) {
> >> -		/* can't support alloc cache if we turn off polling */
> >> -		bio_clear_flag(bio, BIO_PERCPU_CACHE);
> >> -		bio->bi_opf &= ~REQ_HIPRI;
> >> -	}
> >> +	if (!test_bit(QUEUE_FLAG_POLL, &q->queue_flags))
> >> +		bio_clear_hipri(bio);
> > 
> > Since BIO_PERCPU_CACHE doesn't work without REQ_HIRPI, should this check
> > look more like this?
> > 
> > 	if (!test_bit(QUEUE_FLAG_POLL, &q->queue_flags))
> > 		bio->bi_opf &= ~REQ_HIPRI;
> > 	if (!(bio->bi_opf & REQ_HIPRI))
> > 		bio_clear_flag(bio, BIO_PERCPU_CACHE);
> > 
> > I realise the only BIO_PERCPU_CACHE user in this series never sets it
> > without REQ_HIPRI, but it looks like a problem waiting to happen if
> > nothing enforces this pairing: someone could set the CACHE flag on a
> > QUEUE_FLAG_POLL enabled queue without setting HIPRI and get the wrong
> > bio_put() action.
> 
> I'd rather turn that into a WARN_ON or similar. But probably better to
> do that on the freeing side, honestly. That'll be the most reliable way,
> but a shame to add cycles to the hot path...

Yeah, it is a coding error if that happened, so a WARN sounds okay. I
also don't like adding these kinds of checks, so please feel free to not
include it if you think the usage is clear enough.

  reply	other threads:[~2021-08-13 20:31 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-12 15:41 [PATCHSET v5 0/6] Enable bio recycling for polled IO Jens Axboe
2021-08-12 15:41 ` [PATCH 1/6] bio: optimize initialization of a bio Jens Axboe
2021-08-12 16:16   ` Christoph Hellwig
2021-08-12 15:41 ` [PATCH 2/6] fs: add kiocb alloc cache flag Jens Axboe
2021-08-12 16:20   ` Christoph Hellwig
2021-08-12 15:41 ` [PATCH 3/6] bio: add allocation cache abstraction Jens Axboe
2021-08-12 16:32   ` Christoph Hellwig
2021-08-12 16:39     ` Jens Axboe
2021-08-12 15:41 ` [PATCH 4/6] block: clear BIO_PERCPU_CACHE flag if polling isn't supported Jens Axboe
2021-08-12 16:33   ` Christoph Hellwig
2021-08-12 17:31   ` Keith Busch
2021-08-12 17:41     ` Jens Axboe
2021-08-13 20:17       ` Keith Busch
2021-08-13 20:19         ` Jens Axboe
2021-08-13 20:31           ` Keith Busch [this message]
2021-08-13 20:33             ` Jens Axboe
2021-08-12 15:41 ` [PATCH 5/6] io_uring: enable use of bio alloc cache Jens Axboe
2021-08-12 16:39   ` Christoph Hellwig
2021-08-12 16:46     ` Jens Axboe
2021-08-12 15:41 ` [PATCH 6/6] block: use the percpu bio cache in __blkdev_direct_IO Jens Axboe
  -- strict thread matches above, loose matches on Subject: below --
2021-08-11 19:35 [PATCHSET v4 0/6] Enable bio recycling for polled IO Jens Axboe
2021-08-11 19:35 ` [PATCH 4/6] block: clear BIO_PERCPU_CACHE flag if polling isn't supported Jens Axboe

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20210813203138.GA2761@dhcp-10-100-145-180.wdc.com \
    --to=kbusch@kernel.org \
    --cc=axboe@kernel.dk \
    --cc=hch@infradead.org \
    --cc=io-uring@vger.kernel.org \
    --cc=linux-block@vger.kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).