Commit d5eb3a74 authored Oct 09, 2015 by Ian Abbott Committed by Greg Kroah-Hartman Oct 13, 2015

staging: comedi: don't use mutex when polling file



The main mutex in a comedi device can get held for quite a while when
processing comedi instructions, so for performance reasons, the "read"
and "write" file operations do not use it; they use use the
`attach_lock` rwsemaphore to protect against the comedi device becoming
detached at an inopportune moment.  Do the same for the "poll" file
operation.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 3834234f

drivers/staging/comedi/comedi_fops.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -2264,7 +2264,7 @@ static unsigned int comedi_poll(struct file file, poll_table wait)
		struct comedi_device *dev = cfp->dev;
		struct comedi_subdevice s, s_read;

		mutex_lock(&dev->mutex);
		down_read(&dev->attach_lock);

		if (!dev->attached) {
		dev_dbg(dev->class_dev, "no driver attached\n");
		@@ -2294,7 +2294,7 @@ static unsigned int comedi_poll(struct file file, poll_table wait)
		}

		done:
		mutex_unlock(&dev->mutex);
		up_read(&dev->attach_lock);
		return mask;
		}

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