On Fri, 2010-02-05 at 12:17 +0200, Adrian Hunter wrote:
> 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
I don't think this is this commit fault.
The problem lies somewhere in block layer.
del_disk hangs if called while usrspace is frozen.
Because I assume that this code was tested, I guess that it was possible
to call del_disk in this way once.
Fixing CONFIG_MMC_UNSAFE_RESUME=n not to do del_disk, won't be easy...
Best regards,
Maxim Levitsky
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