On Monday 11 February 2008 13:46:25 Ingo Molnar wrote: > > * Andi Kleen <[EMAIL PROTECTED]> wrote: > > > The memory hotadd code assumes that the pud always exists already, but > > that might be not true. Allocate it if it isn't there. > > ok, this seems an like an ancient memory-hotplug bug.
Yes. > Does anyone even > use memory hotplug currently? I don't know. > Did you find this bug via review, or did > it trigger in practice? Review. > > Also, your fix, while it solves a real bug we want to fix, is not quite > right for upstream integration yet. I can see 3 immediate problems with > it: > > > + if (!pud_present(*pud)) { > > + pud = (pud_t *)get_zeroed_page(GFP_ATOMIC); > > the GFP_ATOMIC here can fail. The memory hotplug code already uses GFP_ATOMIC elsewhere (spp_getpage) > The proper solution is to instead extend init_memory_mapping() with a > gfp_t parameter and pass in GFP_ATOMIC from the early init code (where > we must not schedule and where GFP_ATOMIC will succeed anyway), but do a > GFP_KERNEL from arch_add_memory(). The existing code already does GFP_ATOMIC. I admit I haven't double checked why it does that (didn't read the complete path) but I assume it takes a spin lock somewhere. If there is no lock doing a general clean up of all of them would probably make sense. But it would be orthogonal to my patch and I don't think it's needed to fix this concrete bug. The gfp argument is not needed though because this case can be already distingushed by checking after_bootmem. > The proper solution is to extend init_memory_mapping() with a return > value, and to check in the caller. arch_add_memory() obviously does not > want to panic(), it wants to return -ENOMEM to mm/memory_hotplug.c. The existing code already panics elsewhere (spp_getpage); i just copied that. So in summary the panic&GFP_ATOMIC use are not good (I agree), but it's not worse than what was in there before. -Andi -- 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/