On Thursday, 1-Mar-2007 at 7:22 PST, Andrew Morton wrote: > On Thu, 01 Mar 2007 03:47:39 -0800 Zachary Amsden <[EMAIL PROTECTED]> wrote: > > > Rusty Russell wrote: > > > On Thu, 2007-03-01 at 03:34 -0800, Zachary Amsden wrote: > > > > > >> What would be really, really nice would be to statically check all > > >> callsites that issue irq disables actually keep irqs disabled. > > >> Presumably, there was a reason they disabled irqs, and re-enabling them > > >> underneath their noses, even if it is to avoid a race, breaks the logic > > >> behind that reason. > > >> > > > > > > For the moment, how about a BUG_ON() in on_each_cpu()? > > > > > > > Sounds quite decent. But why does on_each_cpu need to disable > > interrupts at all? It just calls func(), then re-enables interrupts. > > So whatever was going to happen during func() that might not be > > interrupt safe could just be done in the callee, avoiding the rather > > expensive mess of disabling and re-enabling interrupts for those cases > > where it doesn't matter. > > The handler for smp_call_function() is called with local interrupts > disabled (from the IPI handler). > > So to provide a consistent call environment for that handler, on_each_cpu() > will also disable local interrupts when making the direct call on this CPU.
And further, this "consistent call environment" is *required* for correct operation of certain callers, e.g. invalidate_bh_lrus(), whose callback function is invalidate_bh_lru(). If invalidate_bh_lru() is called without IRQs blocked, it might be interrupted by an IPI that causes nested execution of that same function on behalf of another cpu's call to on_each_cpu(), and this can lead to duplicate brelse() calls on a buf head (and ultimately to ext3 journaling crashes due to invalid concurrent use of that buf head). Cheers. -ernie - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
