Re: [PATCH 5/8] zram: handle add_disk() & blk_register_region() return value

Sergey Senozhatsky
2015-11-09T01:06:15Z

On (11/06/15 17:52), Vishnu Pratap Singh wrote:
> This patch adds error handling for blk_register_region(),
> register_disk(), add_disk(), disk_alloc_events() & disk_add_events().
> add_disk() & register_disk() functions error handling is very much
> needed as this is used mainly by many modules like mmc, zram, mtd, scsi etc.
> But there is no error handling and it may cause stability issues also.

hm... I came across "FIXME: error handling" comment in add_disk() some
time ago and after a quick google search I found this:
https://lkml.org/lkml/2007/7/24/207

>> The attached patch fixes the problem by changing the prototype of
>> add_disk() and register_disk() to return errors.

Al Viro wrote:

> This is bogus. Just what would callers do with these error values?
> Ignore them silently? Bail out? Can't do - at that point disk just
> might have been opened already. add_disk() is the point of no return;
> we are already past the last point where we could bail out.

> drivers/block/z2ram.c | 12 ++++++++++--
> drivers/block/zram/zram_drv.c | 9 ++++++---

those are different drivers, split the patches (well, if add_disk()
change actually makes sense).

> 2 files changed, 16 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/block/z2ram.c b/drivers/block/z2ram.c
> index 968f9e5..85e841f 100644
> --- a/drivers/block/z2ram.c
> +++ b/drivers/block/z2ram.c
> @@ -364,12 +364,20 @@ z2_init(void)
> sprintf(z2ram_gendisk->disk_name, "z2ram");
>
> z2ram_gendisk->queue = z2_queue;
> - add_disk(z2ram_gendisk);
> - blk_register_region(MKDEV(Z2RAM_MAJOR, 0), Z2MINOR_COUNT, THIS_MODULE,
> + ret = add_disk(z2ram_gendisk);
> + if (ret)
> + goto out_add_disk;
> +
> + ret = blk_register_region(MKDEV(Z2RAM_MAJOR, 0), Z2MINOR_COUNT, THIS_MODULE,
> z2_find, NULL, NULL);
> + if (ret)
> + goto out_blk_reg;

A separate nitpick. z2_init() coding styles need to be 'fixed'. So the
patch will not violate the kernel coding styles.

./scripts/checkpatch.pl
WARNING: please, no spaces at the start of a line
#113: FILE: drivers/block/z2ram.c:367:
+ ret = add_disk(z2ram_gendisk);$

WARNING: please, no spaces at the start of a line
#114: FILE: drivers/block/z2ram.c:368:
+ if (ret)$

WARNING: please, no spaces at the start of a line
#117: FILE: drivers/block/z2ram.c:371:
+ ret = blk_register_region(MKDEV(Z2RAM_MAJOR, 0), Z2MINOR_COUNT,
THIS_MODULE,$

WARNING: please, no spaces at the start of a line
#119: FILE: drivers/block/z2ram.c:373:
+ if (ret)$

total: 0 errors, 4 warnings, 50 lines checked

>
> return 0;
>
> +out_blk_reg:
> + del_gendisk(z2ram_gendisk);
> +out_add_disk:
> out_queue:

Hm... a fall-through empty `out_add_disk' label?

-ss

> put_disk(z2ram_gendisk);
> out_disk:
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index 81a557c..f3d7a49 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -1261,14 +1261,16 @@ static int zram_add(void)
> zram->disk->queue->limits.discard_zeroes_data = 0;
> queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, zram->disk->queue);
>
> - add_disk(zram->disk);
> + ret = add_disk(zram->disk);
> + if (ret)
> + goto out_free_disk;
>
> ret = sysfs_create_group(&disk_to_dev(zram->disk)->kobj,
> &zram_disk_attr_group);
> if (ret < 0) {
> pr_err("Error creating sysfs group for device %d\n",
> device_id);
> - goto out_free_disk;
> + goto out_del_disk;
> }
> strlcpy(zram->compressor, default_compressor, sizeof(zram->compressor));
> zram->meta = NULL;
> @@ -1277,8 +1279,9 @@ static int zram_add(void)
> pr_info("Added device: %s\n", zram->disk->disk_name);
> return device_id;
>
> -out_free_disk:
> +out_del_disk:
> del_gendisk(zram->disk);
> +out_free_disk:
> put_disk(zram->disk);

> out_free_queue:
> blk_cleanup_queue(queue);
> --
> 1.9.1
>