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Commit 25f2f3da authored by Rafael J. Wysocki's avatar Rafael J. Wysocki Committed by Andi Kleen
Browse files

snapshot: Use pm_mutex for mutual exclusion 



We can avoid taking the BKL in snapshot_ioctl() if pm_mutex is used to prevent
the ioctls from being executed concurrently.

In addition, although it is only possible to open /dev/snapshot once, the task
which has done that may spawn a child that will inherit the open descriptor,
so in theory they can call snapshot_write(), snapshot_read() and
snapshot_release() concurrently.  pm_mutex can also be used for mutual
exclusion in such cases.

Signed-off-by: default avatarRafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: default avatarAndi Kleen <ak@linux.intel.com>
Acked-by: default avatarPavel Machek <pavel@suse.cz>
Signed-off-by: default avatarLen Brown <len.brown@intel.com>
parent 52d11025

kernel/power/user.c

+42 −26
Original line number Diff line number Diff line
@@ -70,16 +70,22 @@ static int snapshot_open(struct inode *inode, struct file *filp) 
	struct snapshot_data *data;

	int error;



	if (!atomic_add_unless(&snapshot_device_available, -1, 0))

		return -EBUSY;

	mutex_lock(&pm_mutex);



	if (!atomic_add_unless(&snapshot_device_available, -1, 0)) {

		error = -EBUSY;

		goto Unlock;

	}



	if ((filp->f_flags & O_ACCMODE) == O_RDWR) {

		atomic_inc(&snapshot_device_available);

		return -ENOSYS;

		error = -ENOSYS;

		goto Unlock;

	}

	if(create_basic_memory_bitmaps()) {

		atomic_inc(&snapshot_device_available);

		return -ENOMEM;

		error = -ENOMEM;

		goto Unlock;

	}

	nonseekable_open(inode, filp);

	data = &snapshot_state;
@@ -99,33 +105,36 @@ static int snapshot_open(struct inode *inode, struct file *filp) 
		if (error)

			pm_notifier_call_chain(PM_POST_HIBERNATION);

	}

	if (error) {

	if (error)

		atomic_inc(&snapshot_device_available);

		return error;

	}

	data->frozen = 0;

	data->ready = 0;

	data->platform_support = 0;



	return 0;

 Unlock:

	mutex_unlock(&pm_mutex);



	return error;

}



static int snapshot_release(struct inode *inode, struct file *filp)

{

	struct snapshot_data *data;



	mutex_lock(&pm_mutex);



	swsusp_free();

	free_basic_memory_bitmaps();

	data = filp->private_data;

	free_all_swap_pages(data->swap);

	if (data->frozen) {

		mutex_lock(&pm_mutex);

	if (data->frozen)

		thaw_processes();

		mutex_unlock(&pm_mutex);

	}

	pm_notifier_call_chain(data->mode == O_WRONLY ?

			PM_POST_HIBERNATION : PM_POST_RESTORE);

	atomic_inc(&snapshot_device_available);



	mutex_unlock(&pm_mutex);



	return 0;

}
@@ -135,9 +144,13 @@ static ssize_t snapshot_read(struct file *filp, char __user *buf, 
	struct snapshot_data *data;

	ssize_t res;



	mutex_lock(&pm_mutex);



	data = filp->private_data;

	if (!data->ready)

		return -ENODATA;

	if (!data->ready) {

		res = -ENODATA;

		goto Unlock;

	}

	res = snapshot_read_next(&data->handle, count);

	if (res > 0) {

		if (copy_to_user(buf, data_of(data->handle), res))
@@ -145,6 +158,10 @@ static ssize_t snapshot_read(struct file *filp, char __user *buf, 
		else

			*offp = data->handle.offset;

	}



 Unlock:

	mutex_unlock(&pm_mutex);



	return res;

}
@@ -154,6 +171,8 @@ static ssize_t snapshot_write(struct file *filp, const char __user *buf, 
	struct snapshot_data *data;

	ssize_t res;



	mutex_lock(&pm_mutex);



	data = filp->private_data;

	res = snapshot_write_next(&data->handle, count);

	if (res > 0) {
@@ -162,6 +181,9 @@ static ssize_t snapshot_write(struct file *filp, const char __user *buf, 
		else

			*offp = data->handle.offset;

	}



	mutex_unlock(&pm_mutex);



	return res;

}
@@ -180,16 +202,16 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd, 
	if (!capable(CAP_SYS_ADMIN))

		return -EPERM;



	data = filp->private_data;

	if (!mutex_trylock(&pm_mutex))

		return -EBUSY;



	lock_kernel();

	data = filp->private_data;



	switch (cmd) {



	case SNAPSHOT_FREEZE:

		if (data->frozen)

			break;

		mutex_lock(&pm_mutex);

		printk("Syncing filesystems ... ");

		sys_sync();

		printk("done.\n");
@@ -197,7 +219,6 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd, 
		error = freeze_processes();

		if (error)

			thaw_processes();

		mutex_unlock(&pm_mutex);

		if (!error)

			data->frozen = 1;

		break;
@@ -205,9 +226,7 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd, 
	case SNAPSHOT_UNFREEZE:

		if (!data->frozen || data->ready)

			break;

		mutex_lock(&pm_mutex);

		thaw_processes();

		mutex_unlock(&pm_mutex);

		data->frozen = 0;

		break;
@@ -310,16 +329,11 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd, 
			error = -EPERM;

			break;

		}

		if (!mutex_trylock(&pm_mutex)) {

			error = -EBUSY;

			break;

		}

		/*

		 * Tasks are frozen and the notifiers have been called with

		 * PM_HIBERNATION_PREPARE

		 */

		error = suspend_devices_and_enter(PM_SUSPEND_MEM);

		mutex_unlock(&pm_mutex);

		break;



	case SNAPSHOT_PLATFORM_SUPPORT:
@@ -392,7 +406,9 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd, 
		error = -ENOTTY;



	}

	unlock_kernel();



	mutex_unlock(&pm_mutex);



	return error;

}