linux-kernel - Re: [PATCH v2 2/3] dm: Export function dm_suspend

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Date:	Fri, 17 Jul 2015 16:22:51 +0200
From:	Pali Rohár <pali.rohar@...il.com>
To:	Mike Snitzer <snitzer@...hat.com>
Cc:	Alasdair Kergon <agk@...hat.com>, Neil Brown <neilb@...e.de>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	linux-raid@...r.kernel.org, dm-devel@...hat.com,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH v2 2/3] dm: Export function dm_suspend_md()

On Friday 17 July 2015 10:04:39 Mike Snitzer wrote:
> On Sun, Jun 21 2015 at  7:20am -0400,
> Pali Rohár <pali.rohar@...il.com> 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@...il.com>
> > ---
> >  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?

-- 
Pali Rohár
pali.rohar@...il.com
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