From d5eb3a742109015cd794e536fe0968197b917e05 Mon Sep 17 00:00:00 2001
From: Ian Abbott <abbotti@mev.co.uk>
Date: Fri, 9 Oct 2015 12:26:52 +0100
Subject: [PATCH] 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>
---
drivers/staging/comedi/comedi_fops.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
index 1d6bef285821..fe25287c5688 100644
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -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;
}
--
2.34.1