Messages in this thread | | | Date | Wed, 8 Jul 2009 14:47:44 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH/RFC] sched: Remove SYSTEM_RUNNING checks from cond_resched*() |
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(belatedly cc'ing netdev)
Original diagnosis:
: Using early netconsole and gianfar driver this error pops up: : : netconsole: timeout waiting for carrier : : It appears that net/core/netpoll.c:netpoll_setup() is using : cond_resched() in a loop waiting for a carrier. : : The thing is that cond_resched() is a no-op when system_state != : SYSTEM_RUNNING, and so drivers/net/phy/phy.c's state_queue is never : scheduled, therefore link detection doesn't work
> On Thu, 9 Jul 2009 01:33:31 +0400 Anton Vorontsov <avorontsov@ru.mvista.com> wrote: > On Wed, Jul 08, 2009 at 02:10:24PM -0700, Andrew Morton wrote: > > > On Wed, 8 Jul 2009 09:12:30 -0700 (PDT) Linus Torvalds <torvalds@linux-foundation.org> wrote: > > > That said, I do agree that maybe SYSTEM_RUNNING isn't the right check. > > > Testing that the scheduler is initialized may be the more correct one. I > > > think the SYSTEM_RUNNING one just comes from that being used for other > > > debug issues. > > > > Agreed. system_state is too general. > > > > If we specifically want to know whether it is safe to call schedule() then > > let's create a global boolean it_is_safe_to_call_schedule and test that, > > rather than testing something which indirectly and unreliably implies "it > > is safe to call schedule". If that boolean already exists then no-brainer. > > > > All that being said, I wonder if the netconsole code should be using > > msleep(1) instead. Spinning on cond_resched() is a bit rude. But one > > would have to verify that it is safe to call schedule() at this time, and > > for the netconsole caller, this is dubious. > > What do you mean by "verify that it is safe"? If it works, > can I assume that it's safe? ;-) It works, fwiw. >
netconsole is supposed to be available as early as possible in boot for obvious reasons. I'd say there's a decent risk now and in the future that netconsole will be initialised prior to the scheduler being available.
In fact, if "netconsole: timeout waiting for carrier" newly added to netpoll_setup() a depedency on the scheduler being available then perhaps that was an incorrect change.
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