On 24.09.24 09:45, Geert Uytterhoeven wrote:
Hi Günter,
CC kbuild
I have two comments...
On Tue, Sep 24, 2024 at 1:52 AM Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
On 9/23/24 15:08, Guenter Roeck wrote:
On 9/23/24 08:23, David Hildenbrand wrote:
On 23.09.24 16:25, Guenter Roeck wrote:
SPLIT_PTE_PTLOCKS already depends on "NR_CPUS >= 4", but that evaluates
to true if there is no NR_CPUS configuration option (such as for m68k).
This results in CONFIG_SPLIT_PTE_PTLOCKS=y for mac_defconfig.
This in turn causes the m68k "q800" machine to crash in qemu.
Should this be fixed in Kconfig (too)?
Oh, that's why my compile tests still worked ... I even removed the additional NR_CPUS check, assuming it's not required ...
Thanks for debugging and fixing!
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Apparently it wasn't that simple :-(. 0-day reports a build failure
with s390 builds.
arch/s390/mm/gmap.c:357:16: error: implicit declaration of function 'pmd_pgtable_page'.
Turns out that
depends on NR_CPUS && NR_CPUS >= 4
doesn't work and disables SPLIT_PTE_PTLOCKS even if NR_CPUS _is_ defined.
I have no idea how to declare the dependency correctly.
Sorry, I did not expect that.
The only solution I found was to define NR_CPUS for m68k. That seems to be
the only architecture not defining it, so hopefully that is an acceptable
solution. I'll send v2 of the patch shortly.
My first thought was to agree, as m68k is indeed the only architecture
that does not define NR_CPUS. Upon closer look, most architectures
have NR_CPUS depend on SMP, hence I assume the issue could happen for
those too (although I didn't manage to create such a config on anything
I recall that I played the same thing, convincing me that having no
CONFIG_NR_CPUS on !SMP would actually do the right thing. Apparently it doesn't
for m68k at least.
but m68k)? So the simple solution would be to add a dependency on
SMP to SPLIT_PTE_PTLOCKS.
That will probably work for now. CONFIG_NR_CPUS should be cleaned up at some point
to sort out the FIXME I commented in v2. Having kconfig set CONFIG_NR_CPUS=1 without
SMP would be easiest, but it's probably not that easy.
BTW, the list of excluded architectures looks fragile to me:
config SPLIT_PTE_PTLOCKS
def_bool y
depends on MMU
depends on NR_CPUS >= 4
depends on !ARM || CPU_CACHE_VIPT
depends on !PARISC || PA20
depends on !SPARC32
If this can't be handled in a generic way, perhaps this should be
changed from opt-out to opt-in (i.e. select gate symbol in arch-specific
Kconfig)?
Yes, as stated in my commit:
More cleanups would be reasonable (like the arch-specific "depends on" for
CONFIG_SPLIT_PTE_PTLOCKS), but we'll leave that for another day.
--
Cheers,
David / dhildenb
