On Friday 17 July 2015 17:30:45 Mike Snitzer wrote:
> On Fri, Jul 17 2015 at 11:22am -0400,
>
> Mike Snitzer <snitzer@xxxxxxxxxx> wrote:
> > On Fri, Jul 17 2015 at 10:22am -0400,
> >
> > Pali Rohár <pali.rohar@xxxxxxxxx> wrote:
> > > On Friday 17 July 2015 10:04:39 Mike Snitzer wrote:
> > > > On Sun, Jun 21 2015 at 7:20am -0400,
> > > >
> > > > Pali Rohár <pali.rohar@xxxxxxxxx> wrote:
> > > > > This patch exports function dm_suspend_md() which suspend
> > > > > mapped device so other kernel drivers can use it and could
> > > > > suspend mapped device when needed.
> > > > >
> > > > > Signed-off-by: Pali Rohár <pali.rohar@xxxxxxxxx>
> > > > > ---
> > > > >
> > > > > drivers/md/dm.c | 6 ++++++
> > > > > drivers/md/dm.h | 5 +++++
> > > > > 2 files changed, 11 insertions(+)
> > > > >
> > > > > diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> > > > > index 2caf492..03298ff 100644
> > > > > --- a/drivers/md/dm.c
> > > > > +++ b/drivers/md/dm.c
> > > > >
> > > > > @@ -3343,6 +3343,12 @@ out:
> > > > > return r;
> > > > >
> > > > > }
> > > > >
> > > > > +int dm_suspend_md(struct mapped_device *md)
> > > > > +{
> > > > > + return dm_suspend(md, DM_SUSPEND_LOCKFS_FLAG);
> > > > > +}
> > > > > +EXPORT_SYMBOL_GPL(dm_suspend_md);
> > > > > +
> > > > >
> > > > > /*
> > > > >
> > > > > * Internal suspend/resume works like userspace-driven
> > > > > suspend. It waits * until all bios finish and prevents
> > > > > issuing new bios to the target drivers.
> > > >
> > > > To do this properly you should be introducing a variant of
> > > > dm_internal_suspend. We currently have two variants:
> > > > dm_internal_suspend_fast
> > > > dm_internal_suspend_noflush
> > > >
> > > > The reason to use a dm_internal_suspend variant is this suspend
> > > > was _not_ initiated by an upper level ioctl (from userspace).
> > > > It was done internally from within the target.
> > > >
> > > > You're explicitly using DM_SUSPEND_LOCKFS_FLAG above.. meaning
> > > > you're interested in flushing all pending IO (in the FS
> > > > layered on dm-crupt, if one exists).
> > > >
> > > > But see the comment in __dm_internal_suspend() about
> > > > TASK_UNINTERRUPTIBLE. If you're OK with the dm-crypt initiated
> > > > suspend being TASK_UNINTERRUPTIBLE then you could just
> > > > introduce:
> > > >
> > > > void dm_internal_suspend_uninterruptible_flush(struct
> > > > mapped_device *md) {
> > > >
> > > > mutex_lock(&md->suspend_lock);
> > > > __dm_internal_suspend(md, DM_SUSPEND_LOCKFS_FLAG);
> > > > mutex_unlock(&md->suspend_lock);
> > > >
> > > > }
> > > > EXPORT_SYMBOL_GPL(dm_internal_suspend_uninterruptible_flush);
> > > >
> > > > Otherwise, there is much more extensive DM core changes needed
> > > > to __dm_internal_suspend() and .presuspend to properly support
> > > > TASK_INTERRUPTIBLE.
> > >
> > > Hi! I will look at dm_internal_suspend. Anyway use case for
> > > suspend is from dm-crypt to do both operations: suspend + key
> > > wipe. It means that without entering key again from userspace,
> > > resume is not possible. So my question is: It is possible to do
> > > internal suspend and then using resume from userspace via ioctl?
> >
> > Good question: no, userspace resume would block waiting for
> > internal resume.
> >
> > Soooo... I'll have to look at your patch 3 to understand why
> > dm-crypt is needing to initiate the suspend internally but then
> > userspace is initiating the resume... this imbalance is
> > concerning.
>
> Why not introduce a new message that allows you to wipe the key after
> suspend? Both initiated from userspace.
There is already message for wiping key and it will success only if dm
is suspended.
But this patch series is fixing another problem: wipe key before
suspend/hibernation action happend and to have it race free it must be
done after userspace is freezed!
--
Pali Rohár
pali.rohar@xxxxxxxxx
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