* 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. Does anyone even
use memory hotplug currently? Did you find this bug via review, or did
it trigger in practice?
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 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().
> + if (!pud)
> + panic("Out of memory");
the panic() here is very rude to the user in the hotplug usecase.
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.
and a small style nit while changing this code:
> + } else
> pud = alloc_low_page(&pud_phys);
please add curly braces to the 'else' branch too. (we generally prefer
symmetrical curly braces) Thanks,
Ingo
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