linux-kernel - Re: btusb "firmware request while host is not available" at resume

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Date:   Tue, 12 Sep 2017 02:13:47 +0200
From:   Gabriel C <nix.or.die@...il.com>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Marcel Holtmann <marcel@...tmann.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tejun Heo <tj@...nel.org>,
        "Gustavo F. Padovan" <gustavo@...ovan.org>,
        Sukumar Ghorai <sukumar.ghorai@...el.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "bluez mailin list (linux-bluetooth@...r.kernel.org)" 
        <linux-bluetooth@...r.kernel.org>
Subject: Re: btusb "firmware request while host is not available" at resume

On 11.09.2017 22:06, Luis R. Rodriguez wrote:
> On Mon, Sep 11, 2017 at 12:29:55PM -0700, Greg Kroah-Hartman wrote:
>> On Mon, Sep 11, 2017 at 07:11:38PM +0200, Luis R. Rodriguez wrote:
>>> On Mon, Sep 11, 2017 at 06:46:47AM -0700, Greg Kroah-Hartman wrote:
>>>> To confirm, reverting this fixes the problem I was seeing in 4.13.  I've
>>>> queued it up for the next 4.13-stable release as well.
>>>
>>> Commit 81f95076281f ("firmware: add sanity check on shutdown/suspend") may
>>> seem kludgy but the reason for it was to cleanup the horrible forced and
>>> required UMH lock even when the UMH lock was *not* even needed, which was later
>>> removed via commit 06a45a93e7d34aa ("firmware: move umh try locks into the umh
>>> code").
>>
>> So what does this mean now that it is reverted?
> 
> We discuss what we should do about upkeeping a warning in the future, as
> I think technically the warning was still valid and it could help avoid
> racy lookups with the filesystem which otherwise could have gone unnoticed.
> 
>>> Removing the old UMH lock even when the UMH lock was *not* needed was the right
>>> thing to do but commit 81f95076281f (("firmware: add sanity check on
>>> shutdown/suspend") was put in place as a safe guard as the lock was also
>>> placing an implicit sanity check on the API. It ensures the API with the cache
>>> was used as designed, otherwise you do run the risk of *not getting the
>>> firmware you may need* -- Marcel seems to acknowledge this possibility.
>>>
>>> It may be possible for us to already have in place safeguards so that upon
>>> resume we are ensuring the path to the firmware *is* available, so IMHO we
>>> should remove this *iff* we can provide this guarantee.  Otherwise the check is
>>> valid. You see, although the UMH lock was bogus, it did implicitly ask the
>>> question: is it safe for *any* helper to run and make assumptions on the
>>> filesystem then?
>>>
>>> In lieu of this question being answered the warning is valid given the design
>>> of the firmware API and the having the cache available as a measure to resolve
>>> this race.
>>
>> I don't understand what you are trying to say here at all.
>>
>> To be specific, what, if anything, is a problem with the current state
>> of Linus's tree (and the next 4.13-stable release)?
> 
> The warning is issued when drivers issue *new* firmware requests on resume. The
> firmware API cache was designed to enable drivers to easily be able to request
> firmware on resume without concern about races against the filesystem, but in order
> for this to work the drivers must have requested the firmware prior to suspend.
> 
>> If something needs to be fixed, can you make a patch showing that?  Or
>> do we also need to revert anything else as well to get back to a "better
>> working" state?
> 
> I took a look at the driver and it seems that btusb_setup_intel_new() is
> not called after the driver is initialized, rather its called only when
> hci_dev_do_open() is called. Its not clear to me how you can end up calling
> this on resume but not prior to this on a running system. Feedback from
> someone more familiar with bt would be useful.

While I really don't know that code I can tell anything about .. however this is _NOT_
about Intel Hardware only .. I trigger that on laptops with Atheros..

So seems like some driver need be fixed before trying something like this again?

Regards,

Gabriel C