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    SubjectRe: [PATCH] firmware loader: don't cancel _nowait requests when helper is not yet available
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    On Saturday 10 March 2012 00:36:59 Greg KH wrote:
    > On Fri, Mar 09, 2012 at 11:30:24PM +0100, Christian Lamparter wrote:
    > > This patch fixes a regression which was introduced by:
    > > "PM: Print a warning if firmware is requested when tasks are frozen"
    > >
    > > request_firmware_nowait does not stall in any system resume paths.
    > > Therefore, I think it is perfectly save to use request_firmware_nowait
    > > from at least the ->complete() callback.
    >
    > Is there code somewhere in the kernel that wants to do this?
    uum, yes: The USB subsystem [Good thing, I'm already talking to you! :-D]

    Take a look at drivers/usb/core/usb.c:

    the ->complete callback is registered to usb_dev_complete(dev*), which
    is just a lengthy wrapper for usb_resume(dev, PMSG_ON).

    Now, let's switch to drivers/usb/core/driver.c:

    usb_resume calls do_unbind_rebind(udev, DO_REBIND) and there we go...
    So any usb driver which uses request_firmware_nowait in .probe is
    a possible target for the warning.

    The one I stumbled across is the pcmcia subsystem. Currently it
    tries to rebind the devices during ->resume but I have already
    sent a patch to postpone that till the ->complete callback comes in.
    <http://lkml.org/lkml/2012/3/3/101>

    > Has commit a144c6a broken it somehow that this fix would resolve it?
    When I read the commit, it only talked only about broken drivers doing
    "request_firmware" during .probe. But it does not mention what should
    be done with "request_firmware_nowait" in such a case at all. I think
    it was just an oversight from all involved parties that just got
    noticed now.

    > > Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
    > > ---
    > > drivers/base/firmware_class.c | 2 +-
    > > 1 files changed, 1 insertions(+), 1 deletions(-)
    > >
    > > diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
    > > index 6c9387d..017e020 100644
    > > --- a/drivers/base/firmware_class.c
    > > +++ b/drivers/base/firmware_class.c
    > > @@ -535,7 +535,7 @@ static int _request_firmware(const struct firmware **firmware_p,
    > >
    > > read_lock_usermodehelper();
    > >
    > > - if (WARN_ON(usermodehelper_is_disabled())) {
    > > + if (WARN_ON(usermodehelper_is_disabled() && !(nowait && uevent))) {
    >
    > What does uevent have to do with things here?
    I found this "useful" comment about uevent in request_firmware_nowait's kdocs:
    * @uevent: sends uevent to copy the firmware image if this flag
    * is non-zero else the firmware copy must be done manually.
    I think this flag controls whenever we want to sent a firmware request event
    to the usermodehelper...
    [No idea why this should ever be 'false', maybe there is a good use-case for
    it when the firmware is built-in... But anyway let's just say I'm as ignorant
    as everybody else and I haven't got a single clue about it.]

    Regards,
    Christian


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