Re: dm ioctl: fix hang in early create error condition
From: Helen Koike
Date: Wed May 15 2019 - 12:14:23 EST
On 5/13/19 10:37 PM, Mike Snitzer wrote:
> On Mon, May 13 2019 at 3:25P -0400,
> Helen Koike <helen.koike@xxxxxxxxxxxxx> wrote:
>> The dm_early_create() function (which deals with "dm-mod.create=" kernel
>> command line option) calls dm_hash_insert() who gets an extra reference
>> to the md object.
>> In case of failure, this reference wasn't being released, causing
>> dm_destroy() to hang, thus hanging the whole boot process.
>> Fix this by calling __hash_remove() in the error path.
>> Fixes: 6bbc923dfcf57d ("dm: add support to directly boot to a mapped device")
>> Cc: stable@xxxxxxxxxxxxxxx
>> Signed-off-by: Helen Koike <helen.koike@xxxxxxxxxxxxx>
>> I tested this patch by adding a new test case in the following test
>> This test was failing, but with this patch it works correctly.
> Thanks for the patch but I'd prefer the following simpler fix. What do
> you think?
> That said, I can provide a follow-on patch (inspired by the patch you
> provided) that encourages more code sharing between dm_early_create()
> and dev_create() by factoring out __dev_create().
> diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
> index c740153b4e52..0eb0b462c736 100644
> --- a/drivers/md/dm-ioctl.c
> +++ b/drivers/md/dm-ioctl.c
> @@ -2117,6 +2117,7 @@ int __init dm_early_create(struct dm_ioctl *dmi,
> + (void) __hash_remove(__find_device_hash_cell(dmi));
> return r;
This doesn't really work for two reasons:
1) __find_device_hash_cell() requires a mutual exclusivity between name,
uuid and dev. In dm_early_create(), dmi can have more then one of these.
2) I can fix (1) by calling __get_name_cell(), as the name is mandatory
anyway, but this function also grabs another reference to the md object,
so I need to add an extra dm_put(md) there:
+ (void) __hash_remove(__get_name_cell(dmi->name));
What do you think? Is this ok?