linux-kernel - Re: [PATCH 3/3] exec: Allow do_coredump to wait for user space pipe readers to complete (v7)

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Message-ID: <20090703101606.GB5764@redhat.com>
Date:	Fri, 3 Jul 2009 12:16:06 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Neil Horman <nhorman@...driver.com>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	earl_chew@...lent.com, andi@...stfloor.org,
	alan@...rguk.ukuu.org.uk
Subject: Re: [PATCH 3/3] exec: Allow do_coredump to wait for user space
	pipe readers to complete (v7)

On 07/02, Neil Horman wrote:
>
> +static void wait_for_dump_helpers(struct file *file)
> +{
> +	struct pipe_inode_info *pipe;
> +
> +	pipe = file->f_path.dentry->d_inode->i_pipe;
> +
> +	pipe_lock(pipe);
> +	pipe->readers++;
> +	pipe->writers--;
> +
> +	while ((pipe->readers > 1) && (!fatal_signal_pending(current))) {
> +		wake_up_interruptible_sync(&pipe->wait);
> +		kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
> +		pipe_wait(pipe);
> +	}

The kernel can hang on UP machine.

Suppose that rt task starts the coredump and then recieves a non-fatal
signal before core_pattern app closes stdin.

In that case this "while()" above becomes a busy-wait loop which never
stops.

Neil, please use signal_pending() as I said. Yes, this means wait_for_
will abort if we recieve a non-fatal signal. But as I said we have other
problems with signals here, when we fix them wait_for_dump_helpers()
will be fixed automatically.

Oleg.

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