From: Jens Axboe <axboe@kernel.dk>
To: Theodore Ts'o <tytso@mit.edu>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-ext4@vger.kernel.org" <linux-ext4@vger.kernel.org>
Subject: Re: What am I doing wrong? submit_bio() suddenly stops working...
Date: Thu, 21 Oct 2010 08:59:46 +0200 [thread overview]
Message-ID: <4CBFE4E2.7050001@kernel.dk> (raw)
In-Reply-To: <E1P8kSE-0001DW-8C@tytso-glaptop>
On 2010-10-21 04:00, Theodore Ts'o wrote:
> Hey Jens,
>
> I've been trying to figure out what I'm doing wrong. I've been trying
> to convert the data writeback bath to use the bio layer. It mostly
> works --- until all of sudden all calls to block_bio_queue(), either via
> submit_bh() or via submit_bio(), start turning into no-ops.
>
> I'm sure I'm doing something wrong, but the bio layer isn't terribly
> well documented, so I'm not sure what it might be. The patch which
> causes the problem can be found be found here:
>
> http://userweb.kernel.org/~tytso/ext4-bio-patches/0006-Ext4-Use-bio-layer-instead-of-buffer-layer-in-mpage_.patch
>
> Here is an except from an ftrace I've been taking to get to the bottom
> of it. It's a combination of some trace_printk's, blktrace, and the
> block_bio_queue tracepoint. The full log can be found at:
>
> http://userweb.kernel.org/~tytso/ext4-bio-patches/kvm-console
>
> It shows all of the blktrace events that shows up after block_bio_queue
> tracepoint, but at some point, after jbd2 or ext4 calls submit_bh() or
> submit_bio(), after the block_bio_queue tracepoint, we stop seeing the
> blktrace events, and it looks like the block I/O layer stops answering
> the phone. No complaints in dmesg, no BUG_ON's, no errors....
>
> If I back out the ext4 bio patches, things work correctly, and as I
> said, I'm pretty sure the bug is in my code. But the failure is
> happening deep in the block I/O stack, and I can't figure out why it's
> failing.
>
> I'm hoping this rings a bell, and perhaps we should consider some of the
> debugging trace_printk's as possible new tracepoints?
>
> Any help you could give me would be greatly appreciated. Ideally, you
> or someone can tell me what stupid thing I'm doing. :-)
I don't see anything immediately wrong with your approach. I suspect
we'll need to see sysrq-t traces of the relevant processes to make a
more educated guess!
--
Jens Axboe
next prev parent reply other threads:[~2010-10-21 6:59 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-10-21 2:00 What am I doing wrong? submit_bio() suddenly stops working Theodore Ts'o
2010-10-21 6:59 ` Jens Axboe [this message]
2010-10-21 16:55 ` Ted Ts'o
2010-10-21 17:41 ` Boaz Harrosh
2010-10-21 18:07 ` Jens Axboe
2010-10-22 13:04 ` Peter Zijlstra
2010-10-22 14:08 ` Jens Axboe
2010-10-21 18:14 ` Ted Ts'o
2010-10-21 18:21 ` Jens Axboe
2010-10-21 17:46 ` Jens Axboe
2010-10-21 21:29 ` Ted Ts'o
2010-10-22 3:34 ` Ted Ts'o
2010-10-22 7:19 ` Jens Axboe
2010-10-23 14:48 ` Ted Ts'o
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