Linux-XFS Archive on lore.kernel.org
 help / color / Atom feed
From: "Darrick J. Wong" <djwong@kernel.org>
To: Christoph Hellwig <hch@lst.de>
Cc: linux-xfs@vger.kernel.org, dchinner@redhat.com,
	christian.brauner@ubuntu.com
Subject: Re: [PATCH 2/3] xfs: avoid buffer deadlocks in inumbers/bulkstat
Date: Wed, 3 Mar 2021 10:57:59 -0800
Message-ID: <20210303185759.GU7269@magnolia> (raw)
In-Reply-To: <20210303064556.GC7499@lst.de>

On Wed, Mar 03, 2021 at 07:45:56AM +0100, Christoph Hellwig wrote:
> On Tue, Mar 02, 2021 at 02:28:28PM -0800, Darrick J. Wong wrote:
> > From: Darrick J. Wong <djwong@kernel.org>
> > 
> > When we're servicing an INUMBERS or BULKSTAT request, grab an empty
> > transaction so that we don't hit an ABBA buffer deadlock if the inode
> > btree contains a cycle.
> > 
> > Found by fuzzing an inode btree pointer to introduce a cycle into the
> > tree (xfs/365).
> > 
> > Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> 
> So basically you want to piggy back on the per-trans recursion using
> xfs_trans_buf_item_match?

Right.

> Why do we need the sb-counter for that?

I was about to say that we need freeze protection to prevent fsfreeze
and inumbers/bulkstat stalling each other out on the buffer LRU, but
then I remembered that Brian changed freeze to wait for IO to complete
without dumping the buffer cache this cycle.  So, I don't think freeze
protection is necessary anymore.

> Can the comments be a little more clear?

/*
 * Grab an empty transaction so that we can use the recursive locking
 * support to detect tree cycles instead of deadlocking.
 */

How does that sound?

> Why don't we want that elsewhere where we're walking the btrees?

I'm merely playing whackamole with tree walks here.  I would guess that
quotacheck will be next for evaluation.

It also occurs to me that inumbers/bulkstat should probably not be
calling copy_to_user() separately for every single record.

--D

  reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-02 22:28 [PATCHSET 0/3] xfs: small fixes for 5.12 Darrick J. Wong
2021-03-02 22:28 ` [PATCH 1/3] xfs: fix quota accounting when a mount is idmapped Darrick J. Wong
2021-03-03  6:43   ` Christoph Hellwig
2021-03-03 14:44   ` Christian Brauner
2021-03-03 18:33     ` Darrick J. Wong
2021-03-03 19:09       ` Christian Brauner
2021-03-02 22:28 ` [PATCH 2/3] xfs: avoid buffer deadlocks in inumbers/bulkstat Darrick J. Wong
2021-03-03  6:45   ` Christoph Hellwig
2021-03-03 18:57     ` Darrick J. Wong [this message]
2021-03-02 22:28 ` [PATCH 3/3] xfs: force log and push AIL to clear pinned inodes when aborting mount Darrick J. Wong
2021-03-03  6:48   ` Christoph Hellwig
2021-03-03 19:02     ` Darrick J. Wong
2021-03-02 23:07 ` [PATCHSET 0/3] xfs: small fixes for 5.12 Christian Brauner

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=20210303185759.GU7269@magnolia \
    --to=djwong@kernel.org \
    --cc=christian.brauner@ubuntu.com \
    --cc=dchinner@redhat.com \
    --cc=hch@lst.de \
    --cc=linux-xfs@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

Linux-XFS Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-xfs/0 linux-xfs/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-xfs linux-xfs/ https://lore.kernel.org/linux-xfs \
		linux-xfs@vger.kernel.org
	public-inbox-index linux-xfs

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-xfs


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git