[dm-devel] [PATCH] dm verity: skip verity work on I/O errors when system is shutting down

[hyeongseok]

On 12/5/20 8:03 AM, Sami Tolvanen wrote:
> On Thu, Dec 3, 2020 at 3:46 PM hyeongseok <hyeongseok at gmail.com> wrote:
>> On 12/4/20 2:22 AM, Sami Tolvanen wrote:
>>> Hi,
>>>
>>> On Wed, Dec 2, 2020 at 4:48 PM Hyeongseok Kim <hyeongseok at gmail.com> wrote:
>>>> If emergency system shutdown is called, like by thermal shutdown,
>>>> dm device could be alive when the block device couldn't process
>>>> I/O requests anymore. In this status, the handling of I/O errors
>>>> by new dm I/O requests or by those already in-flight can lead to
>>>> a verity corruption state, which is misjudgment.
>>>> So, skip verity work for I/O error when system is shutting down.
>>> Thank you for the patch. I agree that attempting to correct I/O errors
>>> when the system is shutting down, and thus generating more I/O that's
>>> likely going to fail, is not a good idea.
>>>
>>>> Signed-off-by: Hyeongseok Kim <hyeongseok at gmail.com>
>>>> ---
>>>>    drivers/md/dm-verity-target.c | 12 +++++++++++-
>>>>    1 file changed, 11 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c
>>>> index f74982dcbea0..ba62c537798b 100644
>>>> --- a/drivers/md/dm-verity-target.c
>>>> +++ b/drivers/md/dm-verity-target.c
>>>> @@ -64,6 +64,15 @@ struct buffer_aux {
>>>>           int hash_verified;
>>>>    };
>>>>
>>>> +/*
>>>> + * While system shutdown, skip verity work for I/O error.
>>>> + */
>>>> +static inline bool verity_is_system_shutting_down(void)
>>>> +{
>>>> +       return system_state == SYSTEM_HALT || system_state == SYSTEM_POWER_OFF
>>>> +               || system_state == SYSTEM_RESTART;
>>>> +}
>>> Which of these states does the system get to during an emergency
>>> shutdown? Can we simplify this by changing the test to system_state >
>>> SYSTEM_RUNNING?
>> I only saw that it was SYSTEM_POWER_OFF or SYSTEM_RESTART, I wonder if
>> I/O error can occur in SYSTEM_SUSPEND state.
> OK, so think the current version is fine then.
>
>> As far as I know, this could be happen in emergency shutdown case,
>> can you explain if you have a case when I/O error can occur by
>> SYSTEM_SUSPEND?
> No, I don't have a case where that would happen.
>
>>> Otherwise, this looks good to me. However, I'm now wondering if an I/O
>>> error should ever result in verity_handle_err() being called. Without
>>> FEC, dm-verity won't call verity_handle_err() when I/O fails, but with
>>> FEC enabled, it currently does, assuming error correction fails. Any
>>> thoughts?
>> Yes, I have thought about this, and to be honest, I think verity or FEC
>> should not call verity_handle_error() in case of I/O errors.
> I tend to agree. We could simply check the original bio->bi_status in
> verity_verify_io() and if we failed to correct an I/O error, return an
> error instead of going into verity_handle_err(). Any thoughts?
>
>> But, because I couldn't know the ability of FEC, I only focused on not
>> breaking curent logics other than system shutdown && I/O errors case.
> Sure, makes sense. We can addrwess that separately.
Sounds reasonable. I hope the next improvements.
>
> Reviewed-by: Sami Tolvanen <samitolvanen at google.com>
>
> Sami
>
Thank you for the review.

Hyeongseok