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Re: [PATCH 11/19] xfs: Convert to new freezing code

To: Jan Kara <jack@xxxxxxx>
Subject: Re: [PATCH 11/19] xfs: Convert to new freezing code
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Fri, 9 Mar 2012 10:20:41 +1100
Cc: LKML <linux-kernel@xxxxxxxxxxxxxxx>, linux-fsdevel@xxxxxxxxxxxxxxx, Al Viro <viro@xxxxxxxxxxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, dchinner@xxxxxxxxxx, sandeen@xxxxxxxxxx, Kamal Mostafa <kamal@xxxxxxxxxxxxx>, Ben Myers <bpm@xxxxxxx>, Alex Elder <elder@xxxxxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <1330963277-26336-12-git-send-email-jack@xxxxxxx>
References: <1330963277-26336-1-git-send-email-jack@xxxxxxx> <1330963277-26336-12-git-send-email-jack@xxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Mon, Mar 05, 2012 at 05:01:09PM +0100, Jan Kara wrote:
> Generic code now blocks all writers from standard write paths. So we block all
> writers coming from ioctl and replace blocking of transactions on frozen
> filesystem with a debugging check. As a bonus, we get a protection of ioctl
> against racing remount read-only. We also convert xfs_file_aio_write() to a
> non-racy freeze protection.
....
> diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
> index 329b06a..6468a2a 100644
> --- a/fs/xfs/xfs_trans.c
> +++ b/fs/xfs/xfs_trans.c
> @@ -577,7 +577,6 @@ xfs_trans_alloc(
>       xfs_mount_t     *mp,
>       uint            type)
>  {
> -     xfs_wait_for_freeze(mp, SB_FREEZE_TRANS);
>       return _xfs_trans_alloc(mp, type, KM_SLEEP);
>  }

So what is there to stop internal XFS threads from starting
transactions when the filesystem is frozen? Previously this
SB_FREEZE_TRANS would guarantee even internal fucntions would get
stopped, but now there's nothing?

I do beleive that ext4 has the same problem (the issue reported with
the lazy inode init background thread), and I can see that any other
filesystem that can make modifications via internal triggers will
see the same problem - freeze doesn't block them any more...

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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