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Message-Id: <1245202532.2560.402.camel@ymzhang>
Date: Wed, 17 Jun 2009 09:35:32 +0800
From: "Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
To: Jens Axboe <jens.axboe@...cle.com>
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
chris.mason@...cle.com, david@...morbit.com, hch@...radead.org,
akpm@...ux-foundation.org, jack@...e.cz, richard@....demon.co.uk,
damien.wyart@...e.fr, dedekind1@...il.com, fweisbec@...il.com
Subject: Re: [PATCH 0/15] Per-bdi writeback flusher threads v10
On Tue, 2009-06-16 at 10:00 +0200, Jens Axboe wrote:
> On Tue, Jun 16 2009, Zhang, Yanmin wrote:
> > On Fri, 2009-06-12 at 14:54 +0200, Jens Axboe wrote:
> > > Hi,
> > >
> > > Here's the 10th version of the writeback patches. Changes since v9:
> > >
> > > - Fix bdi task exit race leaving work on the list, flush it after we
> > > know we cannot be found anymore.
> > > - Rename flusher tasks from bdi-foo to flush-foo. Should make it more
> > > clear to the casual observer.
> > > - Fix a problem with the btrfs bdi register patch that would spew
> > > warnings for > 1 mounted btrfs file system.
> > > - Rebase to current -git, there were some conflicts with the latest work
> > > from viro/hch.
> > > - Fix a block layer core problem were stacked devices would overwrite
> > > the bdi state, causing problems and warning spew.
> > > - In bdi_writeback_all(), in the race occurence of a work allocation
> > > failure, restart scanning from the beginning. Then we can drop the
> > > bdi_lock mutex before diving into bdi specific writeback.
> > > - Convert bdi_lock to a spinlock.
> > > - Use spin_trylock() in bdi_writeback_all(), if this isn't a data
> > > integrity writeback. Debatable, I kind of like it...
> > > - Get rid of BDI_CAP_FLUSH_FORKER, just check for match with the
> > > default_backing_dev_info.
> > > - Fix race in list checking in bdi_forker_task().
> > >
> > >
> > > For ease of patching, I've put the full diff here:
> > >
> > > http://kernel.dk/writeback-v10.patch
> > Jens,
> >
> > I applied the patch to 2.6.30 and got a confliction. The attachment is
> > the patch I ported to 2.6.30. Did I miss anything?
> >
> >
> > With the patch, kernel reports below messages on 2 machines.
> >
> > INFO: task sync:29984 blocked for more than 120 seconds.
> > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> > sync D ffff88002805e300 6168 29984 24581
> > ffff88022f84b780 0000000000000082 7fffffffffffffff ffff880133dbfe70
> > 0000000000000000 ffff88022e2b4c50 ffff88022e2b4fd8 00000001000c7bb8
> > ffff88022f513fd0 ffff880133dbfde8 ffff880133dbfec8 ffff88022d5d13c8
> > Call Trace:
> > [<ffffffff802b69e4>] ? bdi_sched_wait+0x0/0xd
> > [<ffffffff80780fde>] ? schedule+0x9/0x1d
> > [<ffffffff802b69ed>] ? bdi_sched_wait+0x9/0xd
> > [<ffffffff8078158d>] ? __wait_on_bit+0x40/0x6f
> > [<ffffffff802b69e4>] ? bdi_sched_wait+0x0/0xd
> > [<ffffffff80781628>] ? out_of_line_wait_on_bit+0x6c/0x78
> > [<ffffffff8024a426>] ? wake_bit_function+0x0/0x23
> > [<ffffffff802b67ac>] ? bdi_writeback_all+0x12a/0x152
> > [<ffffffff802b6805>] ? generic_sync_sb_inodes+0x31/0xde
> > [<ffffffff802b6935>] ? sync_inodes_sb+0x83/0x88
> > [<ffffffff802b6980>] ? __sync_inodes+0x46/0x8f
> > [<ffffffff802b94f2>] ? do_sync+0x36/0x5a
> > [<ffffffff802b9538>] ? sys_sync+0xe/0x12
> > [<ffffffff8020b9ab>] ? system_call_fastpath+0x16/0x1b
>
> I don't think it is your backport, for some reason the v10 missed a
> change that I think could solve this race. If not, there's another in
> there that I need to look at.
>
> So against your current base, could you try with the below added as
> well? The printk() is just so we can see if this triggers for you or
> not.
>
> diff --git a/mm/backing-dev.c b/mm/backing-dev.c
> index b3e80c5..a065da5 100644
> --- a/mm/backing-dev.c
> +++ b/mm/backing-dev.c
> @@ -384,6 +384,15 @@ static int bdi_start_fn(void *ptr)
> */
> synchronize_srcu(&bdi->srcu);
>
> + /*
> + * Flush any pending work. No more can be added, since
> + * the bdi is no longer discoverable.
> + */
> + if (!list_empty(&bdi->work_list)) {
> + printk("bdi: flushing racy work\n");
I ran testings with the patch. 2 machines reported the same issues when do sync
just after mounting filesystems for testing.
These 2 machines did print out above info. One printed it just before dumping the
blocking info.
I ran a series of test cases. Every case does umount filesystems, then mount
them again for testing.
> + wb_do_writeback(wb);
> + }
> +
> bdi_put_wb(bdi, wb);
> return ret;
> }
>
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