From 2f3fdcd7ce935f6f2899ceab57dc8fe5286db3e1 Mon Sep 17 00:00:00 2001 From: Ian Abbott Date: Fri, 8 Nov 2013 15:03:24 +0000 Subject: [PATCH] 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 Signed-off-by: Greg Kroah-Hartman --- 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 0d8565428abb..a1705ed0b844 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 e2432471c390..70de3558c74e 100644 --- a/drivers/staging/comedi/comedidev.h +++ b/drivers/staging/comedi/comedidev.h @@ -22,6 +22,7 @@ #include #include #include +#include #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; -- 2.30.2