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From:   Pierre Gondois <pierre.gondois@arm.com>
To:     linux-kernel@vger.kernel.org
Cc:     Rob.Herring@arm.com, sudeep.holla@arm.com,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J . Wysocki" <rafael@kernel.org>,
        Linux-Renesas <linux-renesas-soc@vger.kernel.org>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Pierre Gondois <pierre.gondois@arm.com>
Subject: [PATCH -next] cacheinfo: Remove of_node_put() for fw_token
Date:   Tue, 15 Nov 2022 23:05:20 +0100
Message-Id: <20221115220520.2076189-1-pierre.gondois@arm.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

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>
---
 drivers/base/cacheinfo.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/base/cacheinfo.c b/drivers/base/cacheinfo.c
index 04317cde800c..950b22cdb5f7 100644
--- a/drivers/base/cacheinfo.c
+++ b/drivers/base/cacheinfo.c
@@ -317,8 +317,6 @@ static void cache_shared_cpu_map_remove(unsigned int cpu)
 			cpumask_clear_cpu(cpu, &sib_leaf->shared_cpu_map);
 			cpumask_clear_cpu(sibling, &this_leaf->shared_cpu_map);
 		}
-		if (of_have_populated_dt())
-			of_node_put(this_leaf->fw_token);
 	}
 }
 
-- 
2.25.1