linux-kernel - Re: [PATCH 03/32] fs: introduce new ->get_poll_head and ->poll

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Message-ID: <20180111082813.GA760@lst.de>
Date:   Thu, 11 Jan 2018 09:28:13 +0100
From:   Christoph Hellwig <hch@....de>
To:     Al Viro <viro@...IV.linux.org.uk>
Cc:     Christoph Hellwig <hch@....de>, Avi Kivity <avi@...lladb.com>,
        linux-aio@...ck.org, linux-fsdevel@...r.kernel.org,
        netdev@...r.kernel.org, linux-api@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 03/32] fs: introduce new ->get_poll_head and
        ->poll_mask methods

On Thu, Jan 11, 2018 at 05:22:00AM +0000, Al Viro wrote:
> Whee...  The very first ->poll() instance in alphabetic order on pathnames:
> in arch/cris/arch-v10/drivers/gpio.c
> 
> static __poll_t gpio_poll(struct file *file, poll_table *wait)
> {
>         __poll_t mask = 0;
>         struct gpio_private *priv = file->private_data;
>         unsigned long data;
>         unsigned long flags;
> 
>         spin_lock_irqsave(&gpio_lock, flags);
> 
>         poll_wait(file, &priv->alarm_wq, wait);
> 
> IOW, we are doing poll_wait() (== possible GFP_KERNEL __get_free_page()) under
> a spinlock...

Yes.  Another god reason to separate poll_wait and the actual
event check callback..