linux-block.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: "Luis R. Rodriguez" <mcgrof@kernel.org>
To: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: "Luis R. Rodriguez" <mcgrof@kernel.org>,
	Al Viro <viro@zeniv.linux.org.uk>,
	bart.vanassche@wdc.com, ming.lei@redhat.com,
	Ted Ts'o <tytso@mit.edu>,
	"Darrick J. Wong" <darrick.wong@oracle.com>,
	Jiri Kosina <jikos@kernel.org>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Pavel Machek <pavel@ucw.cz>, Len Brown <len.brown@intel.com>,
	linux-fsdevel@vger.kernel.org,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	Juergen Gross <jgross@suse.com>,
	Todd Brandt <todd.e.brandt@linux.intel.com>,
	nborisov@suse.com, Jan Kara <jack@suse.cz>,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	Oliver Neukum <ONeukum@suse.com>,
	oleksandr@natalenko.name,
	Oleg Antonyan <oleg.b.antonyan@gmail.com>,
	Yu Chen <yu.chen.surf@gmail.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Linux PM <linux-pm@vger.kernel.org>,
	linux-block@vger.kernel.org, linux-xfs@vger.kernel.org,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 05/11] fs: add iterate_supers_excl() and iterate_supers_reverse_excl()
Date: Thu, 30 Nov 2017 01:22:59 +0100	[thread overview]
Message-ID: <20171130002259.GY729@wotan.suse.de> (raw)
In-Reply-To: <CAJZ5v0gO49=pXGEdi42Hka=Rf=SqVWp-QSJf9_+bGuOgsHMFig@mail.gmail.com>

On Thu, Nov 30, 2017 at 12:48:15AM +0100, Rafael J. Wysocki wrote:
> On Thu, Nov 30, 2017 at 12:23 AM, Luis R. Rodriguez <mcgrof@kernel.org> wrote:
> > +int iterate_supers_excl(int (*f)(struct super_block *, void *), void *arg)
> > +{
> > +       struct super_block *sb, *p = NULL;
> > +       int error = 0;
> > +
> > +       spin_lock(&sb_lock);
> > +       list_for_each_entry(sb, &super_blocks, s_list) {
> > +               if (hlist_unhashed(&sb->s_instances))
> > +                       continue;
> > +               sb->s_count++;
> > +               spin_unlock(&sb_lock);
> 
> Can anything bad happen if the list is modified at this point by a
> concurrent thread?

The race is theoretical and applies to all users of iterate_supers() as well.

Its certainly worth considering, however given other code is implicated its
not a *new* issue or race. Its the best we can do with the current design.

That said, as I looked at all this code I considered that perhaps super_blocks
deserves its own RCU lock to enable us to do full swap operations on the list,
without having to do these nasty releases in between.

If that's possible / desirable I'd consider it a welcomed future optimization,
and I could give it a shot, however its unclear if this is a requirement for
this feature at this time.

  Luis

  reply	other threads:[~2017-11-30  0:22 UTC|newest]

Thread overview: 47+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-11-29 23:23 [PATCH 00/11] fs: use freeze_fs on suspend/hibernate Luis R. Rodriguez
2017-11-29 23:23 ` [PATCH 01/11] fs: provide unlocked helper for freeze_super() Luis R. Rodriguez
2017-11-30 16:58   ` Jan Kara
2017-11-29 23:23 ` [PATCH 02/11] fs: provide unlocked helper thaw_super() Luis R. Rodriguez
2017-11-30 16:59   ` Jan Kara
2017-11-29 23:23 ` [PATCH 03/11] fs: add frozen sb state helpers Luis R. Rodriguez
2017-11-30 17:13   ` Jan Kara
2017-11-30 19:05     ` Luis R. Rodriguez
2017-12-01 11:47       ` Jan Kara
2017-12-01 21:13         ` Luis R. Rodriguez
2017-12-21 11:03           ` Jan Kara
2018-04-18  0:59             ` Luis R. Rodriguez
2018-04-18 10:12               ` Jan Kara
2018-04-20 18:49               ` Luis R. Rodriguez
2018-04-21 23:53                 ` Jan Kara
2018-04-22  1:22                   ` Luis R. Rodriguez
2018-04-22  2:53     ` Luis R. Rodriguez
2017-11-29 23:23 ` [PATCH 04/11] fs: distinguish between user initiated freeze and kernel initiated freeze Luis R. Rodriguez
2017-11-29 23:23 ` [PATCH 05/11] fs: add iterate_supers_excl() and iterate_supers_reverse_excl() Luis R. Rodriguez
2017-11-29 23:48   ` Rafael J. Wysocki
2017-11-30  0:22     ` Luis R. Rodriguez [this message]
2017-11-30  1:34     ` Dave Chinner
2017-11-30  1:40       ` Rafael J. Wysocki
2017-11-30 16:57   ` Jan Kara
2017-11-29 23:23 ` [PATCH 06/11] fs: freeze on suspend and thaw on resume Luis R. Rodriguez
2017-11-29 23:23 ` [PATCH 07/11] xfs: remove not needed freezing calls Luis R. Rodriguez
2017-11-30 16:21   ` Jan Kara
2017-11-30 20:32     ` Rafael J. Wysocki
2017-11-30 23:30       ` Dave Chinner
2017-11-30 23:40         ` Rafael J. Wysocki
2017-11-29 23:23 ` [PATCH 08/11] ext4: " Luis R. Rodriguez
2017-11-29 23:23 ` [PATCH 09/11] f2fs: " Luis R. Rodriguez
2017-11-29 23:23 ` [PATCH 10/11] nilfs2: " Luis R. Rodriguez
2017-11-29 23:23 ` [PATCH 11/11] jfs: " Luis R. Rodriguez
2017-11-30 16:36 ` [PATCH 00/11] fs: use freeze_fs on suspend/hibernate Yu Chen
2017-11-30 16:41   ` Jiri Kosina
2017-11-30 16:50     ` Yu Chen
2017-12-01 19:05     ` Jeff Layton
2017-12-01 21:51       ` Dave Chinner
2017-11-30 17:01 ` Bart Van Assche
2017-11-30 19:42   ` Luis R. Rodriguez
2017-11-30 20:53     ` Bart Van Assche
2017-11-30 21:03       ` Dave Chinner
2017-11-30 21:51 ` Pavel Machek
2017-12-01  0:44   ` Luis R. Rodriguez
2017-12-13  1:09 ` Rafael J. Wysocki
2017-12-19 16:50   ` Luis R. Rodriguez

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=20171130002259.GY729@wotan.suse.de \
    --to=mcgrof@kernel.org \
    --cc=ONeukum@suse.com \
    --cc=bart.vanassche@wdc.com \
    --cc=boris.ostrovsky@oracle.com \
    --cc=dan.j.williams@intel.com \
    --cc=darrick.wong@oracle.com \
    --cc=jack@suse.cz \
    --cc=jgross@suse.com \
    --cc=jikos@kernel.org \
    --cc=len.brown@intel.com \
    --cc=linux-block@vger.kernel.org \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-pm@vger.kernel.org \
    --cc=linux-xfs@vger.kernel.org \
    --cc=martin.petersen@oracle.com \
    --cc=ming.lei@redhat.com \
    --cc=nborisov@suse.com \
    --cc=oleg.b.antonyan@gmail.com \
    --cc=oleksandr@natalenko.name \
    --cc=pavel@ucw.cz \
    --cc=rafael@kernel.org \
    --cc=rjw@rjwysocki.net \
    --cc=todd.e.brandt@linux.intel.com \
    --cc=tytso@mit.edu \
    --cc=viro@zeniv.linux.org.uk \
    --cc=yu.chen.surf@gmail.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).