Re: [PATCH -next] cacheinfo: Remove of_node_put() for fw_token

[Geert Uytterhoeven <geert@linux-m68k.org>]

On Tue, Nov 15, 2022 at 11:06 PM Pierre Gondois <pierre.gondois@arm.com> wrote:
> fw_token is used for DT/ACPI systems to identify CPUs sharing caches.
> For DT based systems, fw_token is set to a pointer to a DT node.
>
> commit ("cacheinfo: Decrement refcount in cache_setup_of_node()")
> doesn't increment the refcount of fw_token anymore in
> cache_setup_of_node(). fw_token is indeed used as a token and not
> as a (struct device_node*), so no reference to fw_token should be
> kept.
>
> However, [1] is triggered when hotplugging a CPU multiple times
> since cache_shared_cpu_map_remove() decrements the refcount to
> fw_token at each CPU unplugging, eventually reaching 0.
>
> Remove of_node_put() for fw_token in cache_shared_cpu_map_remove().
>
> [1]
> [   53.651182] ------------[ cut here ]------------
> [   53.651186] refcount_t: saturated; leaking memory.
> [   53.651223] WARNING: CPU: 4 PID: 32 at lib/refcount.c:22 refcount_warn_saturate (lib/refcount.c:22 (discriminator 3))
> [   53.651241] Modules linked in:
> [   53.651249] CPU: 4 PID: 32 Comm: cpuhp/4 Tainted: G        W          6.1.0-rc1-14091-g9fdf2ca7b9c8 #76
> [   53.651261] Hardware name: ARM LTD ARM Juno Development Platform/ARM Juno Development Platform, BIOS EDK II Oct 31 2022
> [   53.651268] pstate: 600000c5 (nZCv daIF -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> [   53.651279] pc : refcount_warn_saturate (lib/refcount.c:22 (discriminator 3))
> [   53.651293] lr : refcount_warn_saturate (lib/refcount.c:22 (discriminator 3))
> [...]
> [   53.651513] Call trace:
> [...]
> [   53.651735] of_node_release (drivers/of/dynamic.c:335)
> [   53.651750] kobject_put (lib/kobject.c:677 lib/kobject.c:704 ./include/linux/kref.h:65 lib/kobject.c:721)
> [   53.651762] of_node_put (drivers/of/dynamic.c:49)
> [   53.651776] free_cache_attributes.part.0 (drivers/base/cacheinfo.c:712)
> [   53.651792] cacheinfo_cpu_pre_down (drivers/base/cacheinfo.c:718)
> [   53.651807] cpuhp_invoke_callback (kernel/cpu.c:247 (discriminator 4))
> [   53.651819] cpuhp_thread_fun (kernel/cpu.c:785)
> [   53.651832] smpboot_thread_fn (kernel/smpboot.c:164 (discriminator 3))
> [   53.651847] kthread (kernel/kthread.c:376)
> [   53.651858] ret_from_fork (arch/arm64/kernel/entry.S:861)
> [   53.651869] ---[ end trace 0000000000000000 ]---
>
> Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
> Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
> Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>

Thanks, this fixes the issue for me!

Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

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