From mboxrd@z Thu Jan  1 00:00:00 1970
From: Dmitry Monakhov <dmonakhov@openvz.org>
Subject: Re: [PATCH 3/3]      vfs: fix filesystem_sync vs write race on rw=>ro remount v2
Date: Tue, 02 Mar 2010 17:04:26 +0300
Message-ID: <87zl2qddlg.fsf@openvz.org>
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Cc: linux-fsdevel@vger.kernel.org, viro@ZenIV.linux.org.uk
To: Jan Kara <jack@suse.cz>
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In-Reply-To: <20100302132911.GB4763@quack.suse.cz> (Jan Kara's message of
	"Tue, 2 Mar 2010 14:29:11 +0100")
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Jan Kara <jack@suse.cz> writes:

> On Sat 27-02-10 03:25:49, Dmitry Monakhov wrote:
>> +/**
>> + * Check whenever is it possible to remount given sb to readonly.
>> + * @sb : super block in question
>> + *
>> + * Caller is responsible to set ST_REMOUNT_RO state before the call.
>> + */
>> +int fs_may_remount_ro(struct super_block *sb)
>> +{
>> +	struct vfsmount *mnt;
>> +	int ret = 1;
>> +	spin_lock(&vfsmount_lock);
>> +	list_for_each_entry(mnt, &sb->s_vfsmount, mnt_sb_list) {
>> +		ret = !mnt_check_writers(mnt, 0);
>> +		if (ret)
>> +			break;
>> +	}
>> +	spin_unlock(&vfsmount_lock);
>> +	/*
>> +	 * If new writer appears after we have checked all vfsmounts.
>> +	 * Then ST_REMOUNT_RO bit will be cleared.
>> +	 */
>> +	if (!test_bit(ST_REMOUNT_RO, &sb->s_state))
>> +		ret = 0;
>> +	return ret;
>> +}
>   This misses the case when the superblock as unlinked-but-open files.
> In such case we have to fail remount RO as well. The original
> fs_may_remount_ro checks for that..
Since file is opened for write one of vfsmnt struct would have non
zero write count. So -EBUSY will be returned from fs_may_remount_ro()
>
> 								Honza