Subject: Re: [PROBLEM] hard-lock with kmemtrace, relayfs, and splice
From: Pekka Enberg <penberg@cs.helsinki.fi>
To: Tom Zanussi <zanussi@comcast.net>
Cc: Eduard - Gabriel Munteanu <eduard.munteanu@linux360.ro>,
       jens.axboe@oracle.com, linux-kernel@vger.kernel.org
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Date: Mon, 13 Oct 2008 09:57:47 +0300
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Hi Tom,

On Fri, 2008-10-10 at 23:58 -0500, Tom Zanussi wrote:
> It looks like you hit the same problem as described here:
> 
> commit 8191ecd1d14c6914c660dfa007154860a7908857
> 
>     splice: fix infinite loop in generic_file_splice_read()
> 
> relay uses the same loop but it never got noticed or fixed.  Can you try
> the following patch:
> 
> diff --git a/kernel/relay.c b/kernel/relay.c
> index 8d13a78..6a4d439 100644
> --- a/kernel/relay.c
> +++ b/kernel/relay.c
> @@ -1318,12 +1318,9 @@ static ssize_t relay_file_splice_read(struct file *in,
>  		if (ret < 0)
>  			break;
>  		else if (!ret) {
> -			if (spliced)
> -				break;
> -			if (flags & SPLICE_F_NONBLOCK) {
> +			if (flags & SPLICE_F_NONBLOCK)
>  				ret = -EAGAIN;
> -				break;
> -			}
> +			break;
>  		}
>  
>  		*ppos += ret;
> 

Indeed. That fixes the deadlock.

However, now I don't get anything to the cpu*.out files if I run
kmemtraced with kmemtrace disabled. If I enable kmemtrace manually and
then run kmemtraced, I do receive some data. I did apply the
kmemtrace-user patch as well.

Hmm?

		Pekka

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