linux-ext4 - Re: Null pointer deref in do_aio

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Message-ID: <Pine.LNX.4.64.1202101013000.1531@cobra.newdream.net>
Date:	Fri, 10 Feb 2012 12:42:04 -0800 (PST)
From:	Sage Weil <sage@...dream.net>
To:	Jeff Moyer <jmoyer@...hat.com>
cc:	linux-ext4@...r.kernel.org
Subject: Re: Null pointer deref in do_aio_submit

On Fri, 10 Feb 2012, Jeff Moyer wrote:
> Sage Weil <sage@...dream.net> writes:
> 
> > I hit the following under a reasonable simple aio workload:
> >
> >  - reasonably heavy load
> >  - lots of threads doing buffered io to random files
> >  - one thread submitting O_DIRECT aio to a single file (journal), all 
> >    sequential (wrapping), 100MB
> >  - probably somewhere between 1 and 50 aios outstanding at any point in 
> >    time.
> >
> > The kernel was v3.2 mainline, plus unrelated btrfs and ceph patches.
> >
> > Is this a known issue?  Any other information that would be helpful?
> 
> I don't know for sure, but could you test with the following commit?
> 69e4747ee9727d660b88d7e1efe0f4afcb35db1b

I'll pull this in and see if it comes up again (this is the first time 
I've seen the crash).

> Also, I'll note that it looks like you are doing O_SYNC + O_DIRECT AIO.
> I'm curious to know what apps use that particular combination.  Is this
> just a test case, or do you have an app which does this in production?

That's what ceph-osd is doing on it's journal.  Rereading the man page 
it's not clear to me what I *should* be doing, though.  Would you use 
O_SYNC (with O_DIRECT) only to make sure the blocks you write to are 
allocated/reachable on crash?  (Or, say, mtime is updated?)

sage


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