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SubjectRe: [PATCH v3] zram: add restriction on dynamic zram device creation
On Mon, Sep 21, 2020 at 09:30:21AM +0800, Yi Wang wrote:
> From: zhanglin <zhang.lin16@zte.com.cn>
>
> Add max_num_devices to limit dynamic zram device creation to prevent
> potential OOM
>
> Signed-off-by: zhanglin <zhang.lin16@zte.com.cn>
> Signed-off-by: Yi Wang <wang.yi59@zte.com.cn>
> ---
> v1->v2:
> change hard-coded initial max_num_devices into configurable way.
> v2->v3:
> Move inc/dec num_devices logic into zram_add/zram_remove.
>
> drivers/block/zram/Kconfig | 7 +++++++
> drivers/block/zram/zram_drv.c | 26 +++++++++++++++-----------
> 2 files changed, 22 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/block/zram/Kconfig b/drivers/block/zram/Kconfig
> index fe7a4b7d30cf..8455e5ec608b 100644
> --- a/drivers/block/zram/Kconfig
> +++ b/drivers/block/zram/Kconfig
> @@ -37,3 +37,10 @@ config ZRAM_MEMORY_TRACKING
> /sys/kernel/debug/zram/zramX/block_state.
>
> See Documentation/admin-guide/blockdev/zram.rst for more information.
> +
> +config ZRAM_DEV_MAX_COUNT
> + int "Max number of zram devices to be created"
> + depends on ZRAM
> + default 256
> + help
> + This option specifies the maximum number of zram devices.
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index 36d49159140f..5e8978095d68 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -43,8 +43,9 @@ static DEFINE_MUTEX(zram_index_mutex);
> static int zram_major;
> static const char *default_compressor = "lzo-rle";
>
> +static unsigned int num_devices;
> /* Module params (documentation at end) */
> -static unsigned int num_devices = 1;
> +static unsigned int max_num_devices = CONFIG_ZRAM_DEV_MAX_COUNT;
> /*
> * Pages that compress to sizes equals or greater than this are stored
> * uncompressed in memory.
> @@ -1878,6 +1879,9 @@ static int zram_add(void)
> struct request_queue *queue;
> int ret, device_id;
>
> + if (num_devices >= max_num_devices)
> + return -ENOSPC;
> +
> zram = kzalloc(sizeof(struct zram), GFP_KERNEL);
> if (!zram)
> return -ENOMEM;
> @@ -1955,6 +1959,7 @@ static int zram_add(void)
> strlcpy(zram->compressor, default_compressor, sizeof(zram->compressor));
>
> zram_debugfs_register(zram);
> + num_devices += 1;
> pr_info("Added device: %s\n", zram->disk->disk_name);
> return device_id;
>
> @@ -1998,6 +2003,7 @@ static int zram_remove(struct zram *zram)
> blk_cleanup_queue(zram->disk->queue);
> put_disk(zram->disk);
> kfree(zram);
> + num_devices -= 1;
> return 0;
> }
>
> @@ -2111,14 +2117,12 @@ static int __init zram_init(void)
> return -EBUSY;
> }
>
> - while (num_devices != 0) {
> - mutex_lock(&zram_index_mutex);
> - ret = zram_add();
> - mutex_unlock(&zram_index_mutex);
> - if (ret < 0)
> - goto out_error;
> - num_devices--;
> - }
> + mutex_lock(&zram_index_mutex);
> + num_devices = 0;
> + ret = zram_add();
> + mutex_unlock(&zram_index_mutex);
> + if (ret < 0)
> + goto out_error;
>
> return 0;
>
> @@ -2135,8 +2139,8 @@ static void __exit zram_exit(void)
> module_init(zram_init);
> module_exit(zram_exit);
>
> -module_param(num_devices, uint, 0);
> -MODULE_PARM_DESC(num_devices, "Number of pre-created zram devices");

Why did you remove num_devices? It's orthgonal with max_num_devices.
If we remove it, users have been used it to create pre-created zram
device will be broken.

If user asked it more than max_num_devices, we could just return the error
in zram_init with simple pr_err to notice configuration wrong.


> +module_param(max_num_devices, uint, 0);
> +MODULE_PARM_DESC(max_num_devices, "Max number of zram devices to be created");
>
> MODULE_LICENSE("Dual BSD/GPL");
> MODULE_AUTHOR("Nitin Gupta <ngupta@vflare.org>");
> --
> 2.17.1


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