Re: 2.6.39-rc4+: Kernel leaking memory during FS scanning, regression?

[Linus Torvalds]

On Tue, Apr 26, 2011 at 10:09 AM, Bruno Prémont
<bonbons@xxxxxxxxxxxxxxxxx> wrote:
>
> Just in case, /proc/$(pidof rcu_kthread)/status shows ~20k voluntary
> context switches and exactly one non-voluntary one.
>
> In addition when rcu_kthread has stopped doing its work
> `swapoff $(swapdevice)` seems to block forever (at least normal shutdown
> blocks on disabling swap device).
> If I get to do it when I get back home I will manually try to swapoff
> and take process traces with sysrq-t.

That "exactly one non-voluntary one" sounds like the smoking gun.

Normally SCHED_FIFO runs until it voluntarily gives up the CPU. That's
kind of the point of SCHED_FIFO. Involuntary context switches happen
when some higher-priority SCHED_FIFO process becomes runnable (irq
handlers? You _do_ have CONFIG_IRQ_FORCED_THREADING=y in your config
too), and maybe there is a bug in the runqueue handling for that case.

Ingo, do you have any tests for SCHED_FIFO scheduling? Particularly
with UP and voluntary preempt?

                          Linus
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