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zram: rework reset and destroy path

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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: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Reported-by: Ganesh 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Sergey Senozhatsky 2015-02-12 15:00:39 -08:00 committed by Linus Torvalds
parent ba6b17d68c
commit a096cafc31
1 changed files with 33 additions and 42 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

75
drivers/block/zram/zram_drv.c
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@ -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);
@ -1112,15 +1112,31 @@ out:
return ret;
}
static void destroy_device(struct zram *zram)
static void destroy_devices(unsigned int nr)
{
sysfs_remove_group(&disk_to_dev(zram->disk)->kobj,
&zram_disk_attr_group);
struct zram *zram;
unsigned int i;
del_gendisk(zram->disk);
put_disk(zram->disk);
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);
blk_cleanup_queue(zram->queue);
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)
@ -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);