Re: [PATCH -next] arch_topology: Fix cache attributes detection in the CPU hotplug path

[<Conor.Dooley@microchip.com>]

On 18/07/2022 18:41, Guenter Roeck wrote:
> On Wed, Jul 13, 2022 at 02:33:44PM +0100, Sudeep Holla wrote:
>> 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 <ionela.voinescu@arm.com>
>> Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
>> ---
>>  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.
>>
>> 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
>>
> 
> arm64, with next-20220718:
> 
> ...
> [    0.823405] Detected PIPT I-cache on CPU1
> [    0.824456] BUG: sleeping function called from invalid context at kernel/locking/semaphore.c:164
> [    0.824550] in_atomic(): 1, irqs_disabled(): 128, non_block: 0, pid: 0, name: swapper/1
> [    0.824600] preempt_count: 1, expected: 0
> [    0.824633] RCU nest depth: 0, expected: 0
> [    0.824899] no locks held by swapper/1/0.
> [    0.825035] irq event stamp: 0
> [    0.825072] hardirqs last  enabled at (0): [<0000000000000000>] 0x0
> [    0.826017] hardirqs last disabled at (0): [<ffff800008158870>] copy_process+0x5e0/0x18e4
> [    0.826123] softirqs last  enabled at (0): [<ffff800008158870>] copy_process+0x5e0/0x18e4
> [    0.826191] softirqs last disabled at (0): [<0000000000000000>] 0x0
> [    0.826764] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.19.0-rc7-next-20220718 #1
> [    0.827397] Call trace:
> [    0.827456]  dump_backtrace.part.0+0xd4/0xe0
> [    0.827574]  show_stack+0x18/0x50
> [    0.827625]  dump_stack_lvl+0x9c/0xd8
> [    0.827678]  dump_stack+0x18/0x34
> [    0.827722]  __might_resched+0x178/0x220
> [    0.827778]  __might_sleep+0x48/0x80
> [    0.827833]  down_timeout+0x2c/0xa0
> [    0.827896]  acpi_os_wait_semaphore+0x68/0x9c
> [    0.827952]  acpi_ut_acquire_mutex+0x4c/0xb8
> [    0.828008]  acpi_get_table+0x38/0xbc
> [    0.828059]  acpi_find_last_cache_level+0x44/0x130
> [    0.828112]  init_cache_level+0xb8/0xcc
> [    0.828165]  detect_cache_attributes+0x240/0x580
> [    0.828217]  update_siblings_masks+0x28/0x270
> [    0.828270]  store_cpu_topology+0x64/0x74
> [    0.828326]  secondary_start_kernel+0xd0/0x150
> [    0.828386]  __secondary_switched+0xb0/0xb4
> 
> I know the problem has already been reported, but I think the backtrace
> above is slightly different.

Aye, I got a different BT on RISC-V + DT - but that should be fixed in
next-20220718. This is a different problem unfortunately.

Thanks,
Conor.