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From: "Rafael J. Wysocki" <rafael@kernel.org>
To: "Luis R. Rodriguez" <mcgrof@kernel.org>
Cc: 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 00:48:15 +0100
Message-ID: <CAJZ5v0gO49=pXGEdi42Hka=Rf=SqVWp-QSJf9_+bGuOgsHMFig@mail.gmail.com> (raw)
In-Reply-To: <20171129232356.28296-6-mcgrof@kernel.org>

On Thu, Nov 30, 2017 at 12:23 AM, Luis R. Rodriguez <mcgrof@kernel.org> wrote:
> There are use cases where we wish to traverse the superblock list
> but also capture errors, and in which case we want to avoid having
> our callers issue a lock themselves since we can do the locking for
> the callers. Provide a iterate_supers_excl() which calls a function
> with the write lock held. If an error occurs we capture it and
> propagate it.
>
> Likewise there are use cases where we wish to traverse the superblock
> list but in reverse order. The new iterate_supers_reverse_excl() helpers
> does this but also also captures any errors encountered.
>
> Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
> ---
>  fs/super.c         | 91 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/fs.h |  2 ++
>  2 files changed, 93 insertions(+)
>
> diff --git a/fs/super.c b/fs/super.c
> index a63513d187e8..885711c1d35b 100644
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -605,6 +605,97 @@ void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
>         spin_unlock(&sb_lock);
>  }
>
> +/**
> + *     iterate_supers_excl - exclusively call func for all active superblocks
> + *     @f: function to call
> + *     @arg: argument to pass to it
> + *
> + *     Scans the superblock list and calls given function, passing it
> + *     locked superblock and given argument. Returns 0 unless an error
> + *     occurred on calling the function on any superblock.
> + */
> +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?

> +
> +               down_write(&sb->s_umount);
> +               if (sb->s_root && (sb->s_flags & SB_BORN)) {
> +                       error = f(sb, arg);
> +                       if (error) {
> +                               up_write(&sb->s_umount);
> +                               spin_lock(&sb_lock);
> +                               __put_super(sb);
> +                               break;
> +                       }
> +               }
> +               up_write(&sb->s_umount);
> +
> +               spin_lock(&sb_lock);
> +               if (p)
> +                       __put_super(p);
> +               p = sb;
> +       }
> +       if (p)
> +               __put_super(p);
> +       spin_unlock(&sb_lock);
> +
> +       return error;
> +}
> +

  reply index

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 [this message]
2017-11-30  0:22     ` Luis R. Rodriguez
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

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