linux-kernel - Re: [take3 1/4] kevent: Core files.

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Date:	Thu, 3 Aug 2006 16:40:34 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Evgeniy Polyakov <johnpol@....mipt.ru>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	Ulrich Drepper <drepper@...hat.com>,
	netdev <netdev@...r.kernel.org>,
	Zach Brown <zach.brown@...cle.com>
Subject: Re: [take3 1/4] kevent: Core files.

On Thursday 03 August 2006 11:46, Evgeniy Polyakov wrote:
> Core files.
>
> This patch includes core kevent files:
>  - userspace controlling
>  - kernelspace interfaces
>  - initialization
>  - notification state machines
>

> +static int kevent_user_wait(struct file *file, struct kevent_user *u,
> +		unsigned int min_nr, unsigned int max_nr, unsigned int timeout,
> +		void __user *buf)
> +{
>

> +	mutex_lock(&u->ctl_mutex);
> +	while (num < max_nr && ((k = kqueue_dequeue_ready(u)) != NULL)) {
> +		if (copy_to_user(buf + num*sizeof(struct ukevent),
> +					&k->event, sizeof(struct ukevent))) {
> +			cerr = -EINVAL;
> +			break;
> +		}


It seems quite wrong to hold ctl_mutex while doing a copy_to_user() (of 
possibly a large amount of data) : A thread can sleep on a page fault and 
other threads cannot make progress.

Eric
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