From: Christoph Hellwig <hch@lst.de>
To: Ming Lei <ming.lei@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>, Brian Foster <bfoster@redhat.com>,
"Darrick J. Wong" <djwong@kernel.org>,
Dave Chinner <dchinner@redhat.com>,
linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: iomap: writeback ioend/bio allocation deadlock risk
Date: Mon, 24 May 2021 17:32:47 +0200 [thread overview]
Message-ID: <20210524153247.GA6041@lst.de> (raw)
In-Reply-To: <YKd1VS5gkzQRn+7x@T590>
On Fri, May 21, 2021 at 04:54:45PM +0800, Ming Lei wrote:
> On Fri, May 21, 2021 at 10:36:35AM +0200, Christoph Hellwig wrote:
> > On Fri, May 21, 2021 at 04:35:03PM +0800, Ming Lei wrote:
> > > Just wondering why the ioend isn't submitted out after it becomes full?
> >
> > block layer plugging? Although failing bio allocations will kick that,
> > so that is not a deadlock risk.
>
> These ioends are just added to one list stored on local stack variable(submit_list),
Yes. But only until the code finished iterating over a page. The
worst case number of bios for a page is PAGE_SIZE / SECTOR_SIZE, and
the bio_set is side to handle that comfortably.
> how can block layer plugging observe & submit them out?
It can't. I was talking about the high-level plug that is held
over multiple pages. At that point the bios are submitted to the
block layer already, but they might be held in a plug. And looking at
the bio_alloc_bioset code we don't actually flush a plug at the moment
in that case. Something like the patch below would do that:
diff --git a/block/bio.c b/block/bio.c
index 44205dfb6b60..5b9d2f4d7c08 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -432,6 +432,7 @@ struct bio *bio_alloc_bioset(gfp_t gfp_mask, unsigned short nr_iovecs,
p = mempool_alloc(&bs->bio_pool, gfp_mask);
if (!p && gfp_mask != saved_gfp) {
+ blk_schedule_flush_plug(current);
punt_bios_to_rescuer(bs);
gfp_mask = saved_gfp;
p = mempool_alloc(&bs->bio_pool, gfp_mask);
next prev parent reply other threads:[~2021-05-24 15:34 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-21 3:27 iomap: writeback ioend/bio allocation deadlock risk Ming Lei
2021-05-21 7:17 ` Christoph Hellwig
2021-05-21 7:31 ` Ming Lei
2021-05-21 7:35 ` Christoph Hellwig
2021-05-21 8:35 ` Ming Lei
2021-05-21 8:36 ` Christoph Hellwig
2021-05-21 8:54 ` Ming Lei
2021-05-24 15:32 ` Christoph Hellwig [this message]
2021-05-24 23:55 ` Dave Chinner
2021-05-25 4:54 ` Ming Lei
2021-05-25 6:28 ` Ming Lei
2021-05-25 8:21 ` Dave Chinner
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=20210524153247.GA6041@lst.de \
--to=hch@lst.de \
--cc=bfoster@redhat.com \
--cc=dchinner@redhat.com \
--cc=djwong@kernel.org \
--cc=linux-block@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=ming.lei@redhat.com \
/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).