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Date: Wed, 9 Oct 2013 09:37:41 -0400
From: Benjamin LaHaise <bcrl@kvack.org>
To: Will Deacon <will.deacon@arm.com>, Kent Overstreet <kmo@daterainc.com>
Cc: linux-aio@kvack.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
Subject: Re: Kernel warning triggered with trinity on 3.12-rc4
Message-ID: <20131009133741.GA16003@kvack.org>
References: <20131008145217.GB21189@mudshark.cambridge.arm.com>
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On Tue, Oct 08, 2013 at 03:52:17PM +0100, Will Deacon wrote:
> Hi guys,
> 
> I've been running trinity on my ARMv7 Cortex-A15 system and managed to
> trigger the following kernel warning:

Adding Kent to the list of recipients since this is in code he wrote.  I'd 
like to try to track down a test case to add to the libaio tests if we can 
figure it out.

		-ben

> 8<---
> 
> [15333.257972] ------------[ cut here ]------------
> [15333.259328] WARNING: CPU: 1 PID: 18717 at fs/aio.c:474 free_ioctx+0x1d0/0x1d4()
> [15333.259894] Modules linked in:
> [15333.260643] CPU: 1 PID: 18717 Comm: kworker/1:0 Not tainted 3.12.0-rc4 #3
> [15333.261580] Workqueue: events free_ioctx
> [15333.261978] [<c00213f8>] (unwind_backtrace+0x0/0xf4) from [<c001e034>] (show_stack+0x10/0x14)
> [15333.263231] [<c001e034>] (show_stack+0x10/0x14) from [<c03c350c>] (dump_stack+0x98/0xd4)
> [15333.264106] [<c03c350c>] (dump_stack+0x98/0xd4) from [<c002c5ac>] (warn_slowpath_common+0x6c/0x88)
> [15333.265132] [<c002c5ac>] (warn_slowpath_common+0x6c/0x88) from [<c002c664>] (warn_slowpath_null+0x1c/0x24)
> [15333.266053] [<c002c664>] (warn_slowpath_null+0x1c/0x24) from [<c01269a0>] (free_ioctx+0x1d0/0x1d4)
> [15333.267097] [<c01269a0>] (free_ioctx+0x1d0/0x1d4) from [<c0041c30>] (process_one_work+0xf4/0x35c)
> [15333.267822] [<c0041c30>] (process_one_work+0xf4/0x35c) from [<c004288c>] (worker_thread+0x138/0x3d4)
> [15333.268766] [<c004288c>] (worker_thread+0x138/0x3d4) from [<c0048058>] (kthread+0xb4/0xb8)
> [15333.269746] [<c0048058>] (kthread+0xb4/0xb8) from [<c001ae78>] (ret_from_fork+0x14/0x3c)
> [15333.270455] ---[ end trace d2466d8d496fd5c9 ]---
> 
> --->8
> 
> So this looks like either somebody else is messing with ctx->reqs_available
> on the ctx freeing path, or we're inadvertently incrementing the
> reqs_available count beyond the queue size. I'm really not familiar with
> this code, but the conditional assignment to avail looks pretty scary given
> that I don't think we hold the ctx->completion_lock and potentially read the
> tail pointer more than once.
> 
> Any ideas? I've not been able to reproduce the problem again with further
> fuzzing (yet).
> 
> Cheers,
> 
> Will

-- 
"Thought is the essence of where you are now."
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