Re: [PATCH v4 6/6] arch_topology: Build cacheinfo from primary CPU

[Geert Uytterhoeven]

Hi Pierre,

On Wed, Jan 4, 2023 at 7:35 PM Pierre Gondois <pierre.gondois@xxxxxxx> wrote:
> commit 3fcbf1c77d08 ("arch_topology: Fix cache attributes detection
> in the CPU hotplug path")
> 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]:
> [    7.560791] BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:46
> [    7.560794] in_atomic(): 1, irqs_disabled(): 128, non_block: 0, pid: 0, name: swapper/111
> [    7.560796] preempt_count: 1, expected: 0
> [    7.560797] RCU nest depth: 1, expected: 1
> [    7.560799] 3 locks held by swapper/111/0:
> [    7.560800]  #0: ffff403e406cae98 (&pcp->lock){+.+.}-{3:3}, at: get_page_from_freelist+0x218/0x12c8
> [    7.560811]  #1: ffffc5f8ed09f8e8 (rcu_read_lock){....}-{1:3}, at: rt_spin_trylock+0x48/0xf0
> [    7.560820]  #2: ffff403f400b4fd8 (&zone->lock){+.+.}-{3:3}, at: rmqueue_bulk+0x64/0xa80
> [    7.560824] irq event stamp: 0
> [    7.560825] hardirqs last  enabled at (0): [<0000000000000000>] 0x0
> [    7.560827] hardirqs last disabled at (0): [<ffffc5f8e9f7d594>] copy_process+0x5dc/0x1ab8
> [    7.560830] softirqs last  enabled at (0): [<ffffc5f8e9f7d594>] copy_process+0x5dc/0x1ab8
> [    7.560833] softirqs last disabled at (0): [<0000000000000000>] 0x0
> [    7.560834] Preemption disabled at:
> [    7.560835] [<ffffc5f8e9fd3c28>] migrate_enable+0x30/0x130
> [    7.560838] CPU: 111 PID: 0 Comm: swapper/111 Tainted: G        W          6.0.0-rc4-rt6-[...]
> [    7.560841] Call trace:
> [...]
> [    7.560870]  __kmalloc+0xbc/0x1e8
> [    7.560873]  detect_cache_attributes+0x2d4/0x5f0
> [    7.560876]  update_siblings_masks+0x30/0x368
> [    7.560880]  store_cpu_topology+0x78/0xb8
> [    7.560883]  secondary_start_kernel+0xd0/0x198
> [    7.560885]  __secondary_switched+0xb0/0xb4
>
> Signed-off-by: Pierre Gondois <pierre.gondois@xxxxxxx>
> Reviewed-by: Sudeep Holla <sudeep.holla@xxxxxxx>
> Acked-by: Palmer Dabbelt <palmer@xxxxxxxxxxxx>

Thanks for your patch, which is now commit 5944ce092b97caed
("arch_topology: Build cacheinfo from primary CPU") in
driver-core/driver-core-next.

> --- a/drivers/base/arch_topology.c
> +++ b/drivers/base/arch_topology.c
> @@ -736,7 +736,7 @@ void update_siblings_masks(unsigned int cpuid)
>
>         ret = detect_cache_attributes(cpuid);
>         if (ret && ret != -ENOENT)
> -               pr_info("Early cacheinfo failed, ret = %d\n", ret);
> +               pr_info("Early cacheinfo allocation failed, ret = %d\n", ret);
>
>         /* update core and thread sibling masks */
>         for_each_online_cpu(cpu) {
> @@ -825,7 +825,7 @@ __weak int __init parse_acpi_topology(void)
>  #if defined(CONFIG_ARM64) || defined(CONFIG_RISCV)
>  void __init init_cpu_topology(void)
>  {
> -       int ret;
> +       int cpu, ret;
>
>         reset_cpu_topology();
>         ret = parse_acpi_topology();
> @@ -840,6 +840,14 @@ void __init init_cpu_topology(void)
>                 reset_cpu_topology();
>                 return;
>         }
> +
> +       for_each_possible_cpu(cpu) {
> +               ret = fetch_cache_info(cpu);
> +               if (ret) {
> +                       pr_err("Early cacheinfo failed, ret = %d\n", ret);

This triggers on all my RV64 platforms (K210, Icicle, Starlight,
RZ/Five).

This seems to be a respin of
https://lore.kernel.org/all/CAMuHMdUBZ791fxCPkKQ6HCwLE4GJB2S35QC=SQ+X8w5Q4C_70g@xxxxxxxxxxxxxx
which had the same issue.

> +                       break;
> +               }
> +       }
>  }
>

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds