linux-kernel - Re: [PATCH] sdio: fix suspend/resume regression

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Date:	Sat, 23 Oct 2010 16:18:50 +0200
From:	Maxim Levitsky <maximlevitsky@...il.com>
To:	Ohad Ben-Cohen <ohad@...ery.com>
Cc:	linux-mmc@...r.kernel.org, Sven Neumann <s.neumann@...mfeld.com>,
	Chris Ball <cjb@...top.org>, Nicolas Pitre <nico@...xnic.net>,
	libertas-dev@...ts.infradead.org,
	"Rafael J. Wysocki" <rjw@...k.pl>, Daniel Mack <daniel@...aq.de>,
	Colin Cross <ccross@...roid.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	stable@...nel.org
Subject: Re: [PATCH] sdio: fix suspend/resume regression

On Sat, 2010-10-23 at 12:09 +0200, Ohad Ben-Cohen wrote:
> Hi Maxim,
> 
> On Fri, Oct 22, 2010 at 1:47 AM, Maxim Levitsky <maximlevitsky@...il.com> wrote:
> > On Wed, 2010-10-13 at 09:31 +0200, Ohad Ben-Cohen wrote:
> >> Fix SDIO suspend/resume regression introduced by
> >> 4c2ef25fe0b847d2ae818f74758ddb0be1c27d8e "mmc: fix all hangs related to
> >> mmc/sd card insert/removal during suspend/resume":
> ...
> >> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> >> index c94565d..515ff39 100644
> >> --- a/drivers/mmc/core/core.c
> >> +++ b/drivers/mmc/core/core.c
> >> @@ -1682,6 +1682,19 @@ int mmc_suspend_host(struct mmc_host *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) {
> > This reintroduces the bug I fixed.
> >
> > if the CONFIG_MMC_UNSAFE_RESUME isn't set (and that is default
> > unfortunately), the host->bus_ops->resume will be NULL (see core/mmc.c
> > mmc_ops), and therefore card will be removed, that will trigger a block
> > device removal, sync, and deadlock).
> 
> Have you reproduced this or is it just a general concern ?
Only a general concern.
> 
> I'm asking this because if CONFIG_MMC_UNSAFE_RESUME isn't set, then
> mmc_pm_notify() will remove the card and detach the bus.
> 
> As a result, host->bus_ops will be unset, and host->bus_dead will be set.
> 
> In this case, mmc_suspend_host() should skip the code you are concerned about.
You are right here.
There is a very unlikely case that suspend of sd/mmc card fails (with
CONFIG_MMC_UNSAFE_RESUME set, and that will trigger the hang, but that
currently isn't possible because both mmc_sd_suspend and mmc_suspend
just return 0 unconditionally).

Btw, two above functions are identical, so some refactoring won't hurt.

So sorry for noise (and bug).

Best regards,
	Maxim Levitsky



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