On 2017/4/12 下午2:26, NeilBrown wrote:
> md allows a new array device to be created by simply
> opening a device file. This make it difficult to
> remove the device and udev is likely to open the device file
> as part of processing the REMOVE event.
>
> There is an alternate mechanism for creating arrays
> by writing to the new_array module parameter.
> When using tools that work with this parameter, it is
> best to disable the old semantics.
> This new module parameter allows that.
>
> Signed-off-by: NeilBrown <neilb@xxxxxxxx>
Acked-by: Coly Li <colyli@xxxxxxx>
> ---
> drivers/md/md.c | 14 +++++++++++++-
> 1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index c3d3bae947a1..a7ab769eacc3 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -174,6 +174,16 @@ static const struct block_device_operations md_fops;
>
> static int start_readonly;
>
> +/*
> + * The original mechanism for creating an md device is to create
> + * a device node in /dev and to open it. This causes races with device-close.
> + * The preferred method is to write to the "new_array" module parameter.
> + * This can avoid races.
> + * Setting create_on_open to false disables the original mechanism
> + * so all the races disappear.
> + */
> +static bool create_on_open = true;
> +
> /* bio_clone_mddev
> * like bio_clone_bioset, but with a local bio set
> */
> @@ -5286,7 +5296,8 @@ static int md_alloc(dev_t dev, char *name)
>
> static struct kobject *md_probe(dev_t dev, int *part, void *data)
> {
> - md_alloc(dev, NULL);
> + if (create_on_open)
> + md_alloc(dev, NULL);
> return NULL;
> }
>
> @@ -9202,6 +9213,7 @@ static int set_ro(const char *val, struct kernel_param *kp)
> module_param_call(start_ro, set_ro, get_ro, NULL, S_IRUSR|S_IWUSR);
> module_param(start_dirty_degraded, int, S_IRUGO|S_IWUSR);
> module_param_call(new_array, add_named_array, NULL, NULL, S_IWUSR);
> +module_param(create_on_open, bool, S_IRUSR|S_IWUSR);
>
> MODULE_LICENSE("GPL");
> MODULE_DESCRIPTION("MD RAID framework");
>
>
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