2013/2/17 Frederic Weisbecker <fweis...@gmail.com>: > 2013/2/17 Linus Torvalds <torva...@linux-foundation.org>: >> On Sun, Feb 17, 2013 at 7:11 AM, Frederic Weisbecker <fweis...@gmail.com> >> wrote: >>> >>> preempt_value_in_interrupt() looks buggy in your patch: it makes >>> invoke_softirq() returning if (val & HARDIRQ_MASK). But that's always >>> true since you have moved further the sub_preempt_count(IRQ_EXIT) >>> further. >> >> No, that's not it. The value hasn't been written back yet, but it already >> did: >> >> + int offset = IRQ_EXIT_OFFSET; >> + int count = preempt_count() - offset; >> >> so the 'count' has the IRQ_EXIT_OFFSET already subtracted. So no, >> HARDIRQ_MASK is *not* always set. > > Another thing. Perhaps we can push the idea of your patch a little > further by re-entering HARDIRQ_OFFSET at the end of the softirq > processing and do the final sub_preempt_count(HARDIRQ_OFFSET) at the > very end of irq_exit(). > > This way irq_exit() looks a bit more simple to me: everything there > becomes considered as in hardirq: (ie: rcu_irq_exit() and > tick_nohz_irq_exit() won't appear anymore as weird special cases) and > we get rid of that IRQ_EXIT_OFFSET hack that fixes the CONFIG_PREEMPT > case. > > I'm attaching an untested patch that modify yours. It's probably > missing some corner cases that rely on in_interrupt() value in > rcu_irq_exit() and tick_nohz_irq_exit() and may be other things.
I messed up preempt_offset_in_interrupt() with in_atomic() code instead of in_interrupt(). Anyway the patch is untested and is more there to get your opinion for now. I'll put some more care on it if people like it. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/