Re: [PATCH 6.1] arch_topology: Build cacheinfo from primary CPU

[Wen Yang <wen.yang@linux.dev>]

On 9/30/25 02:29, Greg Kroah-Hartman wrote:
> On Tue, Sep 30, 2025 at 01:57:40AM +0800, Wen Yang wrote:
>>
>>
>> On 9/29/25 21:21, Greg Kroah-Hartman wrote:
>>> On Sat, Sep 27, 2025 at 01:46:58AM +0800, Wen Yang wrote:
>>>> From: Pierre Gondois <pierre.gondois@arm.com>
>>>>
>>>> commit 5944ce092b97caed5d86d961e963b883b5c44ee2 upstream.
>>>>
>>
>>>> adds a call to detect_cache_attributes() to populate the cacheinfo
>>>> before updating the siblings mask. detect_cache_attributes() allocates
>>>> memory and can take the PPTT mutex (on ACPI platforms). On PREEMPT_RT
>>>> kernels, on secondary CPUs, this triggers a:
>>>>     'BUG: sleeping function called from invalid context' [1]
>>>> as the code is executed with preemption and interrupts disabled.
>>>>
>>>> The primary CPU was previously storing the cache information using
>>>> the now removed (struct cpu_topology).llc_id:
>>>> commit 5b8dc787ce4a ("arch_topology: Drop LLC identifier stash from
>>>> the CPU topology")
>>>>
>>>> allocate_cache_info() tries to build the cacheinfo from the primary
>>>> CPU prior secondary CPUs boot, if the DT/ACPI description
>>>> contains cache information.
>>>> If allocate_cache_info() fails, then fallback to the current state
>>>> for the cacheinfo allocation. [1] will be triggered in such case.
>>>>
>>>> When unplugging a CPU, the cacheinfo memory cannot be freed. If it
>>>> was, then the memory would be allocated early by the re-plugged
>>>> CPU and would trigger [1].
>>>>
>>>> Note that populate_cache_leaves() might be called multiple times
>>>> due to populate_leaves being moved up. This is required since
>>>> detect_cache_attributes() might be called with per_cpu_cacheinfo(cpu)
>>>> being allocated but not populated.
>>>>
>>>> [1]:
>>>>    | BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:46
>>>>    | in_atomic(): 1, irqs_disabled(): 128, non_block: 0, pid: 0, name: swapper/111
>>>>    | preempt_count: 1, expected: 0
>>>>    | RCU nest depth: 1, expected: 1
>>>>    | 3 locks held by swapper/111/0:
>>>>    |  #0:  (&pcp->lock){+.+.}-{3:3}, at: get_page_from_freelist+0x218/0x12c8
>>>>    |  #1:  (rcu_read_lock){....}-{1:3}, at: rt_spin_trylock+0x48/0xf0
>>>>    |  #2:  (&zone->lock){+.+.}-{3:3}, at: rmqueue_bulk+0x64/0xa80
>>>>    | irq event stamp: 0
>>>>    | hardirqs last  enabled at (0):  0x0
>>>>    | hardirqs last disabled at (0):  copy_process+0x5dc/0x1ab8
>>>>    | softirqs last  enabled at (0):  copy_process+0x5dc/0x1ab8
>>>>    | softirqs last disabled at (0):  0x0
>>>>    | Preemption disabled at:
>>>>    |  migrate_enable+0x30/0x130
>>>>    | CPU: 111 PID: 0 Comm: swapper/111 Tainted: G        W          6.0.0-rc4-rt6-[...]
>>>>    | Call trace:
>>>>    |  __kmalloc+0xbc/0x1e8
>>>>    |  detect_cache_attributes+0x2d4/0x5f0
>>>>    |  update_siblings_masks+0x30/0x368
>>>>    |  store_cpu_topology+0x78/0xb8
>>>>    |  secondary_start_kernel+0xd0/0x198
>>>>    |  __secondary_switched+0xb0/0xb4
>>>>
>>>> Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>
>>>> Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
>>>> Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
>>>> Link: https://lore.kernel.org/r/20230104183033.755668-7-pierre.gondois@arm.com
>>>> Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
>>>> Cc: <stable@vger.kernel.org> # 6.1.x: c3719bd:cacheinfo: Use RISC-V's init_cache_level() as generic OF implementation
>>>> Cc: <stable@vger.kernel.org> # 6.1.x: 8844c3d:cacheinfo: Return error code in init_of_cache_level(
>>>> Cc: <stable@vger.kernel.org> # 6.1.x: de0df44:cacheinfo: Check 'cache-unified' property to count cache leaves
>>>> Cc: <stable@vger.kernel.org> # 6.1.x: fa4d566:ACPI: PPTT: Remove acpi_find_cache_levels()
>>>> Cc: <stable@vger.kernel.org> # 6.1.x: bd50036:ACPI: PPTT: Update acpi_find_last_cache_level() to acpi_get_cache_info(
>>>> Cc: <stable@vger.kernel.org> # 6.1.x
>>>
>>> I do not understand, why do you want all of these applied as well?  Can
>>> you just send the full series of commits?
>>>
>> Thanks for your comments, here is the original series:
>> https://lore.kernel.org/all/167404285593.885445.6219705651301997538.b4-ty@arm.com/
>>
>> commit 3fcbf1c77d08 ("arch_topology: Fix cache attributes detection in the
>> CPU hotplug path") introduced a bug, and this series fixed it.
>>
>>>> Signed-off-by: Wen Yang <wen.yang@linux.dev>
>>>
>>> Also, you have changed this commit a lot from the original one, please
>>> document what you did here.
>>>
>> Thanks for the reminder. We just hope to cherry-pick them onto the 6.1
>> stable branch, without modifying the original commit.
>> Also checked again, as follows:
>>
>> $ git cherry-pick c3719bd
>> $ git cherry-pick 8844c3d
>> $ git cherry-pick de0df44
>> $ git cherry-pick fa4d566
>> $ git cherry-pick bd50036
>> $ git cherry-pick 5944ce0
>>
>> $ git format-patch HEAD -1
>>
>> $ diff 0001-arch_topology-Build-cacheinfo-from-primary-CPU.patch
>> 20250927_wen_yang_arch_topology_build_cacheinfo_from_primary_cpu.mbx
> 
> 
> Can you resend these all as a patch series with your signed-off-by on
> them to show that you have tested them?
> 
> And again, the commit here did not seem to match up with the original
> upstream version, but maybe my tools got it wrong.  Resend the series
> and I'll check it again.
> 

Thanks. We will resend this series soon.

--
Best wishes,
Wen