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Commit a096cafc authored by Sergey Senozhatsky's avatar Sergey Senozhatsky Committed by Linus Torvalds
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zram: rework reset and destroy path 



We need to return set_capacity(disk, 0) from reset_store() back to
zram_reset_device(), a catch by Ganesh Mahendran.  Potentially, we can
race set_capacity() calls from init and reset paths.

The problem is that zram_reset_device() is also getting called from
zram_exit(), which performs operations in misleading reversed order -- we
first create_device() and then init it, while zram_exit() perform
destroy_device() first and then does zram_reset_device().  This is done to
remove sysfs group before we reset device, so we can continue with device
reset/destruction not being raced by sysfs attr write (f.e.  disksize).

Apart from that, destroy_device() releases zram->disk (but we still have
->disk pointer), so we cannot acces zram->disk in later
zram_reset_device() call, which may cause additional errors in the future.

So, this patch rework and cleanup destroy path.

1) remove several unneeded goto labels in zram_init()

2) factor out zram_init() error path and zram_exit() into
   destroy_devices() function, which takes the number of devices to
   destroy as its argument.

3) remove sysfs group in destroy_devices() first, so we can reorder
   operations -- reset device (as expected) goes before disk destroy and
   queue cleanup.  So we can always access ->disk in zram_reset_device().

4) and, finally, return set_capacity() back under ->init_lock.

[akpm@linux-foundation.org: tweak comment]
Signed-off-by: default avatarSergey Senozhatsky <sergey.senozhatsky@gmail.com>
Reported-by: default avatarGanesh Mahendran <opensource.ganesh@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent ba6b17d6

drivers/block/zram/zram_drv.c

+33 −42
Original line number Diff line number Diff line
@@ -732,8 +732,9 @@ static void zram_reset_device(struct zram *zram) 
	zram->meta = NULL;

	/* Reset stats */

	memset(&zram->stats, 0, sizeof(zram->stats));



	zram->disksize = 0;

	set_capacity(zram->disk, 0);



	up_write(&zram->init_lock);

}
@@ -826,7 +827,6 @@ static ssize_t reset_store(struct device *dev, 
	/* Make sure all pending I/O is finished */

	fsync_bdev(bdev);

	zram_reset_device(zram);

	set_capacity(zram->disk, 0);



	mutex_unlock(&bdev->bd_mutex);

	revalidate_disk(zram->disk);
@@ -1112,17 +1112,33 @@ static int create_device(struct zram *zram, int device_id) 
	return ret;

}



static void destroy_device(struct zram *zram)

static void destroy_devices(unsigned int nr)

{

	struct zram *zram;

	unsigned int i;



	for (i = 0; i < nr; i++) {

		zram = &zram_devices[i];

		/*

		 * Remove sysfs first, so no one will perform a disksize

		 * store while we destroy the devices

		 */

		sysfs_remove_group(&disk_to_dev(zram->disk)->kobj,

				&zram_disk_attr_group);



		zram_reset_device(zram);



		del_gendisk(zram->disk);

		put_disk(zram->disk);



		blk_cleanup_queue(zram->queue);

	}



	kfree(zram_devices);

	unregister_blkdev(zram_major, "zram");

	pr_info("Destroyed %u device(s)\n", nr);

}



static int __init zram_init(void)

{

	int ret, dev_id;
@@ -1130,64 +1146,39 @@ static int __init zram_init(void) 
	if (num_devices > max_num_devices) {

		pr_warn("Invalid value for num_devices: %u\n",

				num_devices);

		ret = -EINVAL;

		goto out;

		return -EINVAL;

	}



	zram_major = register_blkdev(0, "zram");

	if (zram_major <= 0) {

		pr_warn("Unable to get major number\n");

		ret = -EBUSY;

		goto out;

		return -EBUSY;

	}



	/* Allocate the device array and initialize each one */

	zram_devices = kzalloc(num_devices * sizeof(struct zram), GFP_KERNEL);

	if (!zram_devices) {

		ret = -ENOMEM;

		goto unregister;

		unregister_blkdev(zram_major, "zram");

		return -ENOMEM;

	}



	for (dev_id = 0; dev_id < num_devices; dev_id++) {

		ret = create_device(&zram_devices[dev_id], dev_id);

		if (ret)

			goto free_devices;

			goto out_error;

	}



	pr_info("Created %u device(s) ...\n", num_devices);



	pr_info("Created %u device(s)\n", num_devices);

	return 0;



free_devices:

	while (dev_id)

		destroy_device(&zram_devices[--dev_id]);

	kfree(zram_devices);

unregister:

	unregister_blkdev(zram_major, "zram");

out:

out_error:

	destroy_devices(dev_id);

	return ret;

}



static void __exit zram_exit(void)

{

	int i;

	struct zram *zram;



	for (i = 0; i < num_devices; i++) {

		zram = &zram_devices[i];



		destroy_device(zram);

		/*

		 * Shouldn't access zram->disk after destroy_device

		 * because destroy_device already released zram->disk.

		 */

		zram_reset_device(zram);

	}



	unregister_blkdev(zram_major, "zram");



	kfree(zram_devices);

	pr_debug("Cleanup done!\n");

	destroy_devices(num_devices);

}



module_init(zram_init);