Re: [PATCH] MMC: fix hang if card was removed during suspend andunsafe resume was enabled

[Adrian Hunter]

ext Andrew Morton wrote:
> On Fri,  5 Feb 2010 01:18:15 +0200 Maxim Levitsky <maximlevitsky@xxxxxxxxx> wrote:
>
> > Currently removal of the card leads to del_disk called indirectly by mmc core.
> > This function expects userspace to be running, which isn't when .resume is called
> >
> > Fix that by removing the code that did that in mmc_resume_host. It is possible
> > because card detection logic will kick it later and remove the card.
>
> I don't really understand.  The above implies that to trigger this bug,
> one needs to physically remove the card during a resume operation.  ie:
> a human-vs-computer race.  Sounds unlikely?
>
> So...  exactly what steps does the user need to take to trigger this
> bug?
>
> > Also make mtd workqueue freezeable, so it won't attempt to add/remove the card
> > while userspace is frozen.
> >
> >
> > diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> > index 30acd52..879d48d 100644
> > --- a/drivers/mmc/core/core.c
> > +++ b/drivers/mmc/core/core.c
> > @@ -1257,7 +1257,6 @@ int mmc_suspend_host(struct mmc_host *host, pm_message_t state)
> >  	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) {
> > @@ -1300,15 +1299,11 @@ int mmc_resume_host(struct mmc_host *host)
> >  		mmc_select_voltage(host, host->ocr);
> >  		BUG_ON(!host->bus_ops->resume);
> >  		err = host->bus_ops->resume(host);
> > +
> >  		if (err) {
> >  			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);
>
> afacit that code's been there since March 2009.  I'd have thought that
> someone would have noticed "kernel hangs on resume" before now.
>
> Do you think the patch should be backported into 2.6.32.x and eariler?

It looks like the code was introduced in 2.6.32.x by commit

95cdfb72b9bc568803f395c266152c71b034b461

cc'ing the author Nicolas Pitre

> >  			/* no need to bother upper layers */
> >  			err = 0;
> >  		}
> > @@ -1332,7 +1327,7 @@ static int __init mmc_init(void)
> >  {
> >  	int ret;
> >  
> > -	workqueue = create_singlethread_workqueue("kmmcd");
> > +	workqueue = create_freezeable_workqueue("kmmcd");
> >  	if (!workqueue)
> >  		return -ENOMEM;
> --
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