linux-kernel - Re: [PATCH v6 03/18] of: overlay: add missing of_node_get() in __of_attach_node

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Message-ID: <2b742254-3b54-d862-5126-95ae7d5056f9@gmail.com>
Date:   Wed, 7 Nov 2018 06:57:43 -0800
From:   Frank Rowand <frowand.list@...il.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Rob Herring <robh+dt@...nel.org>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Alan Tull <atull@...nel.org>, Moritz Fischer <mdf@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        devicetree@...r.kernel.org, linux-fpga@...r.kernel.org
Subject: Re: [PATCH v6 03/18] of: overlay: add missing of_node_get() in
 __of_attach_node_sysfs

On 11/7/18 4:14 AM, Michael Ellerman wrote:
> frowand.list@...il.com writes:
> 
>> From: Frank Rowand <frank.rowand@...y.com>
>>
>> There is a matching of_node_put() in __of_detach_node_sysfs()
>>
>> Remove misleading comment from function header comment for
>> of_detach_node().
>>
>> This patch may result in memory leaks from code that directly calls
>> the dynamic node add and delete functions directly instead of
>> using changesets.
>>
>> Tested-by: Alan Tull <atull@...nel.org>
>> Signed-off-by: Frank Rowand <frank.rowand@...y.com>
> 
> This seems sensible to me. I guess we could argue about whether the
> sysfs code needs its own reference, but it certainly doesn't hurt that
> it does, as long as it's handled symmetrically - which it is now.
> 
> Acked-by: Michael Ellerman <mpe@...erman.id.au> (powerpc)
> 
>> ---
>>
>> This patch should result in powerpc systems that dynamically
>> allocate a node, then later deallocate the node to have a
>> memory leak when the node is deallocated.
>>
>> The next patch in the series will fix the leak.
> 
> I think this should go in the changelog, it's useful information that we
> don't want to lose track of once this is applied.

Will do.

-Frank

> 
> Either that or we actually squash the two patches together when applying
> to avoid the bisection break.
> 
> cheers
> 
>>  drivers/of/dynamic.c | 3 ---
>>  drivers/of/kobj.c    | 4 +++-
>>  2 files changed, 3 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/of/dynamic.c b/drivers/of/dynamic.c
>> index 12c3f9a15e94..146681540487 100644
>> --- a/drivers/of/dynamic.c
>> +++ b/drivers/of/dynamic.c
>> @@ -272,9 +272,6 @@ void __of_detach_node(struct device_node *np)
>>  
>>  /**
>>   * of_detach_node() - "Unplug" a node from the device tree.
>> - *
>> - * The caller must hold a reference to the node.  The memory associated with
>> - * the node is not freed until its refcount goes to zero.
>>   */
>>  int of_detach_node(struct device_node *np)
>>  {
>> diff --git a/drivers/of/kobj.c b/drivers/of/kobj.c
>> index 7a0a18980b98..c72eef988041 100644
>> --- a/drivers/of/kobj.c
>> +++ b/drivers/of/kobj.c
>> @@ -133,6 +133,9 @@ int __of_attach_node_sysfs(struct device_node *np)
>>  	}
>>  	if (!name)
>>  		return -ENOMEM;
>> +
>> +	of_node_get(np);
>> +
>>  	rc = kobject_add(&np->kobj, parent, "%s", name);
>>  	kfree(name);
>>  	if (rc)
>> @@ -159,6 +162,5 @@ void __of_detach_node_sysfs(struct device_node *np)
>>  		kobject_del(&np->kobj);
>>  	}
>>  
>> -	/* finally remove the kobj_init ref */
>>  	of_node_put(np);
>>  }
>> -- 
>> Frank Rowand <frank.rowand@...y.com>
>