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

Maxim Levitsky
2010-06-21T20:14:21Z

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.

Best regards,
Maxim Levitsky