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SubjectRe: [PATCH] MMC: fix hang if card was removed during suspend and unsafe resume was enabled
ext Andrew Morton wrote:
> On Fri, 5 Feb 2010 01:18:15 +0200 Maxim Levitsky <maximlevitsky@gmail.com> 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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