Commit 2f3fdcd7 authored Nov 08, 2013 by Ian Abbott Committed by Greg Kroah-Hartman Nov 11, 2013

staging: comedi: add rw_semaphore to protect against device detachment

The 'read' and 'write' file operations on comedi devices do not use the
main mutex in the `struct comedi_device` to avoid contention with ioctls
that may take a while to complete. However, it is necessary to protect
against the device being detached while the operation is in progress.
Add member `struct rw_semaphore attach_lock` to `struct comedi_device`
for this purpose and initialize it on creation.

The actual locking and unlocking will be implemented by subsequent
patches. Tasks that are attaching or detaching comedi devices will
write-acquire the new semaphore whilst also holding the main mutex in
the `struct comedi_device`. Tasks that wish to protect against the
comedi device being detached need to acquire either the main mutex, or
read-acquire the new semaphore, or both in that order.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent ab3cb2e3

drivers/staging/comedi/comedi_fops.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -91,6 +91,7 @@ static void comedi_device_init(struct comedi_device *dev)
		{
		spin_lock_init(&dev->spinlock);
		mutex_init(&dev->mutex);
		init_rwsem(&dev->attach_lock);
		dev->minor = -1;
		}

drivers/staging/comedi/comedidev.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -22,6 +22,7 @@
		#include <linux/dma-mapping.h>
		#include <linux/mutex.h>
		#include <linux/spinlock_types.h>
		#include <linux/rwsem.h>

		#include "comedi.h"

		@@ -184,6 +185,7 @@ struct comedi_device {
		bool ioenabled:1;
		spinlock_t spinlock;
		struct mutex mutex;
		struct rw_semaphore attach_lock;

		int n_subdevices;
		struct comedi_subdevice *subdevices;