From: Chris Mason <chris.mason@oracle.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: Miao Xie <miaox@cn.fujitsu.com>, viro <viro@zeniv.linux.org.uk>,
Linux Btrfs <linux-btrfs@vger.kernel.org>,
Linux Fsdevel <linux-fsdevel@vger.kernel.org>,
Ito <t-itoh@jp.fujitsu.com>
Subject: Re: [PATCH 2/2] Btrfs: fix deadlock on sb->s_umount when doing umount
Date: Tue, 6 Dec 2011 16:36:11 -0500 [thread overview]
Message-ID: <20111206213611.GB4029@shiny> (raw)
In-Reply-To: <20111206112322.GA10836@infradead.org>
On Tue, Dec 06, 2011 at 06:23:23AM -0500, Christoph Hellwig wrote:
> On Tue, Dec 06, 2011 at 07:06:40PM +0800, Miao Xie wrote:
> > > I can't see why you need the writeout when the trylocks fails. Umount
> > > needs to take care of writing out all pending file data anyway, so doing
> > > it from the cleaner thread in addition doesn't sound like it would help.
> >
> > umount invokes sync_fs() and write out all the dirty file data. For the
> > other file systems, its OK because the file system does not introduce dirty pages
> > by itself. But btrfs is different. Its automatic defragment will make lots of dirty
> > pages after sync_fs() and reserve lots of meta-data space for those pages.
> > And then the cleaner thread may find there is no enough space to reserve, it must
> > sync the dirty file data and release the reserved space which is for the dirty
> > file data.
>
> I think the safest way to fix is is to write out all dirty data again
> once the cleaner thread has been safely stopped.
>
Said another way we want to stop the autodefrag code before the unmount
is ready to continue. We also want to stop balancing, scrub etc.
-chris
next prev parent reply other threads:[~2011-12-06 21:36 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-06 5:35 [PATCH 2/2] Btrfs: fix deadlock on sb->s_umount when doing umount Miao Xie
2011-12-06 5:49 ` Al Viro
2011-12-06 6:52 ` Miao Xie
2011-12-06 9:59 ` Christoph Hellwig
2011-12-06 11:06 ` Miao Xie
2011-12-06 11:23 ` Christoph Hellwig
2011-12-06 21:36 ` Chris Mason [this message]
2011-12-07 2:31 ` Miao Xie
2011-12-07 11:11 ` Ilya Dryomov
2011-12-08 3:46 ` Miao Xie
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