Re: [PATCH 1/2] MMC: fix all hangs related to mmc/sd card insert/removal during suspend/resume.

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Tuesday, June 22, 2010, Maxim Levitsky wrote:
> On Mon, 2010-06-21 at 22:26 +0200, Rafael J. Wysocki wrote: 
> > On Monday, June 21, 2010, Maxim Levitsky wrote:
> > > On Mon, 2010-06-21 at 23:04 +0300, Adrian Hunter wrote: 
> > > > ext Maxim Levitsky wrote:
> > > > > If you don't use CONFIG_MMC_UNSAFE_RESUME, as soon as you attempt to
> > > > > suspend, the card will be removed, therefore this patch doesn't change
> > > > > the behavior of this option.
> > > > > 
> > > > > However the removal will be done by pm notifier, which runs while
> > > > > userspace is still not frozen and thus can freely use del_gendisk,
> > > > > without the risk of deadlock which would happen otherwise.
> > > > > 
> > > > > 
> > > > > Card detect workqueue is now freezeable,
> > > > > therefore if you do use CONFIG_MMC_UNSAFE_RESUME,
> > > > > and remove the card during suspend, the removal will be
> > > > > detected as soon as userspace is unfrozen, again at the moment
> > > > > it is safe to call del_gendisk.
> > > > > 
> > > > > Tested with and without CONFIG_MMC_UNSAFE_RESUME with suspend and hibernate.
> > > > > 
> > > > > Signed-off-by: Maxim Levitsky <maximlevitsky@gmail.com>
> > > > > ---
> > > > >  drivers/mmc/core/core.c  |   54 +++++++++++++++++++++++++++------------------
> > > > >  drivers/mmc/core/host.c  |    6 +++++
> > > > >  include/linux/mmc/host.h |    3 ++
> > > > >  3 files changed, 41 insertions(+), 22 deletions(-)
> > > > > 
> > > > > diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> > > > > index 569e94d..0cba53a 100644
> > > > > --- a/drivers/mmc/core/core.c
> > > > > +++ b/drivers/mmc/core/core.c
> > > > > @@ -1259,26 +1259,11 @@ int mmc_suspend_host(struct mmc_host *host)
> > > > >  
> > > > >  	if (host->caps & MMC_CAP_DISABLE)
> > > > >  		cancel_delayed_work(&host->disable);
> > > > > -	cancel_delayed_work(&host->detect);
> > > > > -	mmc_flush_scheduled_work();
> > > > >  
> > > > >  	mmc_bus_get(host);
> > > > >  	if (host->bus_ops && !host->bus_dead) {
> > > > >  		if (host->bus_ops->suspend)
> > > > >  			err = host->bus_ops->suspend(host);
> > > > > -		if (err == -ENOSYS || !host->bus_ops->resume) {
> > > > > -			/*
> > > > > -			 * We simply "remove" the card in this case.
> > > > > -			 * It will be redetected on resume.
> > > > > -			 */
> > > > > -			if (host->bus_ops->remove)
> > > > > -				host->bus_ops->remove(host);
> > > > > -			mmc_claim_host(host);
> > > > > -			mmc_detach_bus(host);
> > > > > -			mmc_release_host(host);
> > > > > -			host->pm_flags = 0;
> > > > > -			err = 0;
> > > > > -		}
> > > > >  	}
> > > > >  	mmc_bus_put(host);
> > > > >  
> > > > > @@ -1310,12 +1295,6 @@ int mmc_resume_host(struct mmc_host *host)
> > > > >  			printk(KERN_WARNING "%s: error %d during resume "
> > > > >  					    "(card was removed?)\n",
> > > > >  					    mmc_hostname(host), err);
> > > > > -			if (host->bus_ops->remove)
> > > > > -				host->bus_ops->remove(host);
> > > > > -			mmc_claim_host(host);
> > > > > -			mmc_detach_bus(host);
> > > > > -			mmc_release_host(host);
> > > > > -			/* no need to bother upper layers */
> > > > >  			err = 0;
> > > > >  		}
> > > > >  	}
> > > > > @@ -1330,6 +1309,37 @@ int mmc_resume_host(struct mmc_host *host)
> > > > >  	return err;
> > > > >  }
> > > > >  
> > > > > +/* Do the card removal on suspend if card is assumed removeable
> > > > > + * Do that in pm notifier while userspace isn't yet frozen, so we will be able
> > > > > +   to sync the card.
> > > > > +*/
> > > > > +int mmc_pm_notify(struct notifier_block *notify_block,
> > > > > +					unsigned long mode, void *unused)
> > > > > +{
> > > > > +	struct mmc_host *host = container_of(
> > > > > +		notify_block, struct mmc_host, pm_notify);
> > > > > +
> > > > > +
> > > > > +	switch (mode) {
> > > > > +	case PM_HIBERNATION_PREPARE:
> > > > > +	case PM_SUSPEND_PREPARE:
> > > > > +
> > > > > +		if (!host->bus_ops || host->bus_ops->suspend)
> > > > > +			break;
> > > > > +
> > > > > +		if (host->bus_ops->remove)
> > > > > +			host->bus_ops->remove(host);
> > > > > +		mmc_claim_host(host);
> > > > > +		mmc_detach_bus(host);
> > > > > +		mmc_release_host(host);
> > > > > +		host->pm_flags = 0;
> > > > > +		break;
> > > > 
> > > > Is it possible that you receive PM_SUSPEND_PREPARE
> > > > but there is no suspend and therefore no resume
> > > > and therefore the card is removed but not detected
> > > > again?
> > > This is very good point.
> > > The solution is to kick mmc detection thread from this notifier.
> > > on resume.
> > > I update the patch.
> > > 
> > > > 
> > > > Is it possible that you are racing with kmmcd and the
> > > > card is added after you receive PM_SUSPEND_PREPARE but
> > > > before kmmcd is frozen?
> > > This is unlikely but valid race.
> > > I afraid I don't know nice way to solve it right now.
> > > I can add some ad-hoc variable to tell interrupt handler not to kick the
> > > detection workqueue after suspend notifier was called.
> > > 
> > > I wish there was a generic freeze_workqueue function.
> > 
> > There are freezable workqueues that are automatically frozen during suspend
> > by the process freezer.  However, at the moment they need to be singlethread
> > and I'm not sure if using one in this particular case is appropriate.
> 
> I *do* use freezable  work-queue.

I overlooked that, sorry.

> However since this is pm notifier, it is called before userspace and the
> workqueue is frozen.
> Therefore I would like manually to freeze the workqueue from the pm
> notifier.

No, that won't work.  You need to find an alternative solution.  I guess you
may insert a work item that's going to sleep until a condition is
satisfied (analogous to a workqueue barrier) and wait for it to run.

Rafael