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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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    > More majordomo info at http://vger.kernel.org/majordomo-info.html
    >



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