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

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Date:	Fri, 17 Jul 2015 10:04:39 -0400
From:	Mike Snitzer <snitzer@...hat.com>
To:	Pali Rohár <pali.rohar@...il.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 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.
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