On Thu, Jul 14, 2022 at 02:17:33PM +0000, Conor.Dooley@microchip.com wrote:

On 13/07/2022 14:33, Sudeep Holla wrote:

Hey Sudeep,
I could not get this patch to actually apply, tried a couple
different versions of -next :/

That's strange.

It is in -next already though, which I suspect might be part of why
it does not apply.. 

Ah that could be the case.

Surely you can fast forward your arch_topology
for-next branch to gregs merge commit rather than generating this
from the premerge branch & re-merging into your branch that Stephen
picks up?

Greg has merged my branch and all those commits are untouched, so it shouldn't
cause any issue as the hash remains same in both the trees, I just added just
this one patch on the top. Did you see any issues with the merge, or are you
just speculating based on your understanding. As I said if Greg had picked
up patches directly, then I would have definitely based on his -next branch
to avoid duplicate hash, but that is not the case here.

Either way, I tested it directly in -next since that's back to
booting for me today and ...

Thanks.

quoted

init_cpu_topology() is called only once at the boot and all the cache
attributes are detected early for all the possible CPUs. However when
the CPUs are hotplugged out, the cacheinfo gets removed. While the
attributes are added back when the CPUs are hotplugged back in as part
of CPU hotplug state machine, it ends up called quite late after the
update_siblings_masks() are called in the secondary_start_kernel()
resulting in wrong llc_sibling_masks.

Move the call to detect_cache_attributes() inside update_siblings_masks()
to ensure the cacheinfo is updated before the LLC sibling masks are
updated. This will fix the incorrect LLC sibling masks generated when
the CPUs are hotplugged out and hotplugged back in again.

Reported-by: Ionela Voinescu <redacted>
Signed-off-by: Sudeep Holla <redacted>
---
  drivers/base/arch_topology.c | 16 ++++++----------
  1 file changed, 6 insertions(+), 10 deletions(-)

Hi Conor,

Ionela reported an issue with the CPU hotplug and as a fix I need to
move the call to detect_cache_attributes() which I had thought to keep
it there from first but for no reason had moved it to init_cpu_topology().

Wonder if this fixes the -ENOMEM on RISC-V as this one is called on the
cpu in the secondary CPUs init path while init_cpu_topology executed
detect_cache_attributes() for all possible CPUs much earlier. I think
this might help as the percpu memory might be initialised in this case.

Actually, we are now worse off than before:
     0.009813] smp: Bringing up secondary CPUs ...
[    0.011530] BUG: sleeping function called from invalid context at include/linux/sched/mm.h:274
[    0.011550] in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 0, name: swapper/1
[    0.011566] preempt_count: 1, expected: 0
[    0.011580] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.19.0-rc6-next-20220714-dirty #1
[    0.011599] Hardware name: Microchip PolarFire-SoC Icicle Kit (DT)
[    0.011608] Call Trace:
[    0.011620] [<ffffffff80005070>] dump_backtrace+0x1c/0x24
[    0.011661] [<ffffffff8066b0c4>] show_stack+0x2c/0x38
[    0.011699] [<ffffffff806704a2>] dump_stack_lvl+0x40/0x58
[    0.011725] [<ffffffff806704ce>] dump_stack+0x14/0x1c
[    0.011745] [<ffffffff8002f42a>] __might_resched+0x100/0x10a
[    0.011772] [<ffffffff8002f472>] __might_sleep+0x3e/0x66
[    0.011793] [<ffffffff8014d774>] __kmalloc+0xd6/0x224
[    0.011825] [<ffffffff803d631c>] detect_cache_attributes+0x37a/0x448
[    0.011855] [<ffffffff803e8fbe>] update_siblings_masks+0x24/0x246
[    0.011885] [<ffffffff80005f32>] smp_callin+0x38/0x5c
[    0.015990] smp: Brought up 1 node, 4 CPUs

Interesting, need to check if it is not in atomic context on arm64.
Wonder if some configs are disabled and making this bug hidden. Let me
check.

One possible solution is to add GFP_ATOMIC to the allocation but I want
to make sure if it is legal to be in atomic context when calling
update_siblings_masks.

quoted

Anyways give this a try, also test the CPU hotplug and check if nothing
is broken on RISC-V. We noticed this bug only on one platform while

So, our system monitor that runs openSBI does not actually support
any hotplug features yet, so:

OK, we can ignore hotplug on RISC-V for now then. We have tested on multiple
arm64 platforms(DT as well as ACPI).

-- 
Regards,
Sudeep

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