On Tue, Jun 10, 2008 at 05:53:08PM +0100, Catalin Marinas wrote: > On Tue, 2008-06-10 at 08:47 -0700, Paul E. McKenney wrote: > > On Tue, Jun 10, 2008 at 03:51:25PM +0100, Catalin Marinas wrote: > > > I was thinking whether this condition can be removed and allow the > > > smp_call_function*() to be called with IRQs disabled. At a quick look, > > > it seems to be possible if the csd_flag_wait() function calls the IPI > > > handlers directly when the IRQs are disabled (see the patch below). > [...] > > There were objections last month: http://lkml.org/lkml/2008/5/3/167 > > Thanks, I missed this discussion. > > > The issue was that this permits some interrupts to arrive despite > > interrupts being disabled. There seemed to be less resistance to > > doing this in the wait==1 case, however. > > The "(wait == 1) && irqs_disabled()" case is what I would be interested > in. In the patch you proposed, this doesn't seem to be allowed (at least > from the use of WARN_ON). However, from your post in May: > > > 5. If you call smp_call_function() with irqs disabled, then you > > are guaranteed that no other CPU's smp_call_function() handler > > will be invoked while smp_call_function() is executing. > > this would be possible but no one need this functionality yet. > > Would one use-case (ARM SMP and DMA cache maintenance) be enough to > implement this or I should add it to the ARM-specific code? How will you implement it? You have to be able to wait *somewhere* (either before or after the smp_call_function call) with interrupts enabled. It is not enough just to eg. use a spinlock around smp_call_function, because other CPUs might also be trying to call down the same path also with interrupts disabled, and they'll wait forever on the spinlock. -- 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
