[systemd-devel] [PATCH] udev: warn instead of killing kmod loading

Greg Kroah-Hartman gregkh at linuxfoundation.org
Sat Aug 9 07:06:44 PDT 2014

On Sat, Aug 09, 2014 at 10:33:47AM +0200, Luis R. Rodriguez wrote:
> On Sat, Aug 09, 2014 at 09:42:36AM +0200, Kay Sievers wrote:
> > On Sat, Aug 9, 2014 at 4:16 AM, Luis R. Rodriguez
> > <mcgrof at do-not-panic.com> wrote:
> > > The purpose of commit e64fae55 (January 2012) on systemd was
> > > to introduce a timeout send to hell drivers that are not using
> > > asynch firmware loading. That commit actually would not have
> > > triggered in full effect on udev's usage of kmod for module
> > > loading until commit 786235ee was merged on Linux (Nov 2013).
> > >
> > > As it is today [ systemd e64fae55 + kernel e64fae55 ] will trigger
> > > a SIGKILL to udev's usage of kmod for module loading after a 30
> > > second timeout. Hannes modified systemd through commit 9719859c
> > > to enable a custom timeout. A different timeout value can only
> > > prevent a kill after a maximum amount of time is known to be
> > > required for a system.
> > >
> > > Penalizing a device driver for not using asynch firmware loading
> > > by killing it and preventing it from loading *might* have originally
> > > been reasonable but its not the only reason why some drivers might
> > > take more than 30 seconds to load. Some drivers might actually
> > > require take over 30 seconds on just writing the firmware to the
> > > hardware. The worst case scenario however would be to run into
> > > storage drivers which might go over the timeout value in which
> > > case currently the system would simply be unbootable. Fixing
> > > drivers should be our *top priority* but the current state of
> > > affairs has proven to make it very difficult to debug why a
> > > driver is failing to load.
> > >
> > > Instead of always forcing a kill lets only warn for workers
> > > handling kmod. This should enable easier methods for determining
> > > which drivers need fixing and the logic would only be used on
> > > workers dealing with kmod module loading.
> > 
> > Nobody wanted to send anything to hell, penalize or force anything
> > anywhere. This kind of language is absolutely not welcome here.
> > 
> > Every operation in systemd, unless specified otherwise, has and needs
> > to have a timeout. The 30 seconds were arbitrarily chosen just to be
> > smaller than the kernel's own 60 second timeout for the userspace
> > firmware loader. Now that userspace firmware loading is gone, this
> > does not apply anymore.
> > 
> > Like everywhere else, we should keep the timeout handling by default.
> > If 60 seconds are too short, we might want to set it to something
> > else.
> Putting emphasis only on firmware loading is exactly what took us to where we
> are today with the current timeout. As we have seen though firmware loading
> though is not what actually takes a lot of time, at times actually writing the
> firmware to hardware can take more time. There are other scenarios which have
> creeped up as well such as delays on other areas of network drivers and storage
> drivers.  We're all in agreement all this needs to be fixed on drivers, however
> in light of these other circumstances and given that it will take time to fix
> these drivers, and given that its hard to debug the cause to current driver
> failures on the timeout a warning for kmod loading would do much more to help
> use fix drivers than a kill.

"time to fix these drivers"?  I posted a 10 line patch to do so for any
driver that has a problem, and another core kernel developer agreed with
it and said it should be made even more general, and easier to use for
all drivers (resulting in only a 1-2 line change per driver affected.)

What happened to that work, has it been dropped for some reason?  Was it
tested and found to not work properly?  Was it rejected by a subsystem
maintainer that I didn't see?


greg k-h

More information about the systemd-devel mailing list