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Date: Mon, 8 Apr 2013 23:57:15 +0100
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Stephen Warren <swarren@wwwdotorg.org>
Cc: Nathan Zimmer <nzimmer@sgi.com>, akpm@linux-foundation.org,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
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        David Woodhouse <dwmw2@infradead.org>, stable@vger.kernel.org,
        "linux-next@vger.kernel.org" <linux-next@vger.kernel.org>
Subject: Re: hangs on boot in 9984d7394618df9
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On Mon, Apr 08, 2013 at 11:46:37PM +0100, Al Viro wrote:

> Very interesting...  Just in case, could you try this on top of that
> branch and see if it triggers?
> 
> diff --git a/fs/pipe.c b/fs/pipe.c
> index 8ce279b..b6cd51b 100644
> --- a/fs/pipe.c
> +++ b/fs/pipe.c
> @@ -1022,6 +1022,11 @@ static int fifo_open(struct inode *inode, struct file *filp)
>  	/* We can only do regular read/write on fifos */
>  	filp->f_mode &= (FMODE_READ | FMODE_WRITE);
>  
> +	if (inode->i_sb->s_magic == PIPEFS_MAGIC) {
> +		WARN_ON(filp->f_flags & O_NONBLOCK);
> +		filp->f_flags &= ~O_NONBLOCK;
> +	}

*d'oh*

OK, I'm an idiot.  I see what's going on now...  Give me a few and I'll push
a fix.