On Thu, 7 Nov 2013, Geert Uytterhoeven wrote: > Hi Thomas, > > On Wed, Nov 6, 2013 at 6:23 PM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > >> Also note that the value of "nested" doesn't match the indentation level, > >> which depends on my own bookkeeping using "nesting". > > > > Well, nested is just an indicator. It's not the nest level. > > I know, the only thing that matters is whether it's zero or not. > But it should always be zero if there's no nesting, and non-zero if there > is, right? > > So: > > # irq 13 nested 1024 > > nested should be 0 here. > > # irq 4 nested 0 > > ok > > # irq 13 nested 1024 > > ok (two extra spaces in front of "irq"). > > # irq 4 nested 0 > > nested should be non-zero here. Hmm. The softirq code reenables interrupts unconditionally. So when an interrupt hits there SR on stack has the bits cleared. You could verify that by checking in_serving_softirq() at the entry to do_IRQ(). That could also explain the irq 4 nests in irq 4 issue. You can't observe that on the original code as the softirq invocation and therefor the interrupt enable happens outside of do_IRQ(). Though that does not explain the non nested case where nested is != 0. But it looks like that irq 13 has a higher level than 4: > # irq 13 nested 1024 > > ok (two extra spaces in front of "irq"). So it could actually be the following: irq X arrives, SR I2/1/0 is set to 4 Now before we reach do_IRQ() irq 13 arrives and interrupts irq X as it has a higher level Your nest accounting shows 0, but the SR says nested, which is actually the correct state. Is there an easy to setup/use emulator around on which I could try to dig into that myself? Thanks, tglx -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
