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..

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