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

[Sami Tolvanen]

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 address that separately.

Reviewed-by: Sami Tolvanen <samitolvanen at google.com>

Sami