linux-kernel - Re: [PATCH 1/2] vfs: Provide function to get superblock and wait for it to thaw

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Message-ID: <20120212211325.GT23916@ZenIV.linux.org.uk>
Date:	Sun, 12 Feb 2012 21:13:25 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Jan Kara <jack@...e.cz>
Cc:	LKML <linux-kernel@...r.kernel.org>, linux-fsdevel@...r.kernel.org,
	Dave Chinner <david@...morbit.com>, mpatocka@...hat.com,
	Eric Sandeen <sandeen@...deen.net>
Subject: Re: [PATCH 1/2] vfs: Provide function to get superblock and wait for
 it to thaw

On Fri, Feb 10, 2012 at 11:03:00AM +0100, Jan Kara wrote:
> In quota code we need to find a superblock corresponding to a device and wait
> for superblock to be unfrozen. However this waiting has to happen without
> s_umount semaphore because that is required for superblock to thaw. So provide
> a function in VFS for this to keep dances with s_umount where they belong.

Eww...  All it takes is
struct super_block *get_super_thawed(struct block_device *bdev)
{
        while (1) {
                struct super_block *s = get_super(bdev);
                if (!s || s->s_frozen == SB_UNFROZEN)
                        return s;
		up_read(&s->s_umount);
		vfs_check_frozen(s, SB_FREEZE_WRITE);
		put_super(s);
        }
}
and there's no need of extra arguments, etc. whatsoever.  Both patches
applied, with implementation of get_super_thawed() done as above.
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