linux-kernel - Re: [BUGFIX] [PATCH] freeze_bdev: don't deactivate successfully frozen MS

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Date:	Sat, 30 Jan 2010 20:44:57 +0200
From:	Thomas Backlund <tmb@...driva.org>
To:	Jun'ichi Nomura <j-nomura@...jp.nec.com>
CC:	Christoph Hellwig <hch@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"tmb@...driva.org" <tmb@...driva.org>,
	Fran?ois Figarola <francois.figarola@...onsult.fr>,
	device-mapper development <dm-devel@...hat.com>,
	Neil Brown <neilb@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-raid@...r.kernel.org" <linux-raid@...r.kernel.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	"stable@...nel.org" <stable@...nel.org>
Subject: Re: [BUGFIX] [PATCH] freeze_bdev: don't deactivate successfully frozen
 MS_RDONLY sb

29.01.2010 02:56, Jun'ichi Nomura skrev:
> Thanks Thomas and Christoph for testing and review.
> I removed 'smp_wmb()' before up_write from the previous patch,
> since up_write() should have necessary ordering constraints.
> (I.e. the change of s_frozen is visible to others after up_write)
> I'm quite sure the change is harmless but if you are uncomfortable
> with Tested-by/Reviewed-by on the modified patch, please remove them.
>

I've just verified that this patch works as intended on both 2.6.32 and 
2.6.33-rc6, so for me it's still OK.
>
> If MS_RDONLY, freeze_bdev should just up_write(s_umount) instead of
> deactivate_locked_super().
> Also, keep sb->s_frozen consistent so that remount can check the frozen state.
>
> Otherwise a crash reported here can happen:
> http://lkml.org/lkml/2010/1/16/37
> http://lkml.org/lkml/2010/1/28/53
>
>
> This patch should be applied for 2.6.32 stable series, too.
>
> Reviewed-by: Christoph Hellwig<hch@....de>
> Tested-by: Thomas Backlund<tmb@...driva.org>
> Signed-off-by: Jun'ichi Nomura<j-nomura@...jp.nec.com>
> Cc: stable@...nel.org
>
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 73d6a73..d11d028 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -246,7 +246,8 @@ struct super_block *freeze_bdev(struct block_device *bdev)
>   	if (!sb)
>   		goto out;
>   	if (sb->s_flags&  MS_RDONLY) {
> -		deactivate_locked_super(sb);
> +		sb->s_frozen = SB_FREEZE_TRANS;
> +		up_write(&sb->s_umount);
>   		mutex_unlock(&bdev->bd_fsfreeze_mutex);
>   		return sb;
>   	}
> @@ -307,7 +308,7 @@ int thaw_bdev(struct block_device *bdev, struct super_block *sb)
>   	BUG_ON(sb->s_bdev != bdev);
>   	down_write(&sb->s_umount);
>   	if (sb->s_flags&  MS_RDONLY)
> -		goto out_deactivate;
> +		goto out_unfrozen;
>
>   	if (sb->s_op->unfreeze_fs) {
>   		error = sb->s_op->unfreeze_fs(sb);
> @@ -321,11 +322,11 @@ int thaw_bdev(struct block_device *bdev, struct super_block *sb)
>   		}
>   	}
>
> +out_unfrozen:
>   	sb->s_frozen = SB_UNFROZEN;
>   	smp_wmb();
>   	wake_up(&sb->s_wait_unfrozen);
>
> -out_deactivate:
>   	if (sb)
>   		deactivate_locked_super(sb);
>   out_unlock:
> .
>

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