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 <abbo...@mev.co.uk>
---
drivers/staging/comedi/comedi_fops.c | 1 +
drivers/staging/comedi/comedidev.h | 2 ++
2 files changed, 3 insertions(+)
diff --git a/drivers/staging/comedi/comedi_fops.c
b/drivers/staging/comedi/comedi_fops.c
index 0d85654..a1705ed 100644
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -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;
}
diff --git a/drivers/staging/comedi/comedidev.h
b/drivers/staging/comedi/comedidev.h
index e243247..70de355 100644
--- a/drivers/staging/comedi/comedidev.h
+++ b/drivers/staging/comedi/comedidev.h
@@ -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;
--
1.8.4.2
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