From: Chris Mason <chris.mason@fusionio.com>
To: Miao Xie <miaox@cn.fujitsu.com>
Cc: "Chris L. Mason" <clmason@fusionio.com>,
Linux Btrfs <linux-btrfs@vger.kernel.org>,
David Sterba <dave@jikos.cz>
Subject: Re: [RFC PATCH] Btrfs: fix full backref problem when inserting shared block reference
Date: Fri, 10 Aug 2012 07:56:28 -0400 [thread overview]
Message-ID: <20120810115628.GE32103@shiny> (raw)
In-Reply-To: <5024E4B7.20600@cn.fujitsu.com>
On Fri, Aug 10, 2012 at 04:38:47AM -0600, Miao Xie wrote:
> On thu, 9 Aug 2012 14:04:05 -0400, Chris Mason wrote:
> > On Wed, Aug 08, 2012 at 09:10:17PM -0600, Miao Xie wrote:
> >> If we create several snapshots at the same time, the following BUG_ON() will be
> >> triggered.
> >>
> >> kernel BUG at fs/btrfs/extent-tree.c:6047!
> >>
> >> Steps to reproduce:
> >> # mkfs.btrfs <partition>
> >> # mount <partition> <mnt>
> >> # cd <mnt>
> >> # for ((i=0;i<2400;i++)); do touch long_name_to_make_tree_more_deep$i; done
> >> # for ((i=0; i<4; i++))
> >> > do
> >> > mkdir $i
> >> > for ((j=0; j<200; j++))
> >> > do
> >> > btrfs sub snap . $i/$j
> >> > done &
> >> > done
> >
> > snapshot creation has a critical section. Once we copy a given root to
> > its snapshot, we're not allowed to change it until the transaction
> > is fully committed.
>
> I knew this critical section. But I think we can kick it away by forcing the
> snapshoted tree to do COW.
Yes, it should be possible.
>
> BTW, I will take a vacation next week, so I can not reply it until the week after next.
> If it is not urgent, I will continue looking into this problem after I come back.
No problem, we can take the current patch for now and improve add back
the ability to do multiple snapshots per root later.
-chris
next prev parent reply other threads:[~2012-08-10 11:56 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-09 3:10 [RFC PATCH] Btrfs: fix full backref problem when inserting shared block reference Miao Xie
2012-08-09 6:48 ` David Sterba
2012-08-09 7:21 ` David Sterba
2012-08-09 7:50 ` Miao Xie
2012-08-10 10:38 ` Miao Xie
2012-08-21 6:24 ` Miao Xie
2012-08-09 12:23 ` Josef Bacik
2012-08-09 13:11 ` Chris Mason
2012-08-09 13:12 ` Josef Bacik
2012-08-09 13:16 ` Chris Mason
2012-08-09 18:04 ` Chris Mason
2012-08-10 10:38 ` Miao Xie
2012-08-10 11:56 ` Chris Mason [this message]
2013-01-30 18:23 ` Alex Lyakas
2013-01-31 2:42 ` Miao Xie
2013-01-31 13:06 ` Alex Lyakas
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