Messages in this thread | | | Date | Tue, 24 Mar 2009 23:01:11 +0100 | From | Ingo Molnar <> | Subject | Re: Revert "gro: Fix legacy path napi_complete crash", |
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* David Miller <davem@davemloft.net> wrote:
> From: Ingo Molnar <mingo@elte.hu> > Date: Tue, 24 Mar 2009 21:54:44 +0100 > > > * Ingo Molnar <mingo@elte.hu> wrote: > > > > > > Same forcedeth box i reported before. Config below. (note: if > > > > you want to use it you need to run it through 'make oldconfig', > > > > with all defaults accepted) > > > > > > Hm, i just had a test failure (hung interface) with this too. > > > > > > I'll go back to the original straight revert of "303c6a0: gro: Fix > > > legacy path napi_complete crash", and will test it overnight - to > > > establish a baseline of stability again. (to make sure there are > > > no other bugs interacting) > > > > FYI, this plain revert is holding up fine in my tests so far - 50 > > random iterations - the previous one failed after 5 iterations. > > Something must be up with respect to letting interrupts in during > certain windows of time, or similar. > > I'll take a look at this and hopefully Herbert or myself will be > able to figure it out.
It definitely did not show usual patterns of bug behavior - i'd have found it yesterday morning if it did.
I spent most of the time trying to find a reliable reproducer .config and system. Sometimes the bug went away with a minor change in the .config. Until today i didnt even suspect a mainline change causing this.
Also, note that i have reduced the probability of UP kernels in my randconfigs artificially to about 12.5% (it is 50% upstream). Still, despite that measure, the 'best' .config i found was an UP config - i dont think that's an accident. Also, i had to fully saturate the target CPU over gigabit to hit the bug best.
Which suggests to me (empirically) that it's indeed a race and that it needs a saturated system with lots of IRQs to trigger, and perhaps that it needs saturated/overloaded network device queues and complex userspace/softirq/hardirq interactions.
Ingo
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