linux-kernel - Re: [PATCH 1/2] vboxsf: Avoid an spurious warning if load_nls

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Date:   Thu, 2 Nov 2023 22:21:51 +0100
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Hans de Goede <hdegoede@...hat.com>,
        Christoph Hellwig <hch@...radead.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 1/2] vboxsf: Avoid an spurious warning if load_nls_xxx()
 fails

Le 02/11/2023 à 13:30, Matthew Wilcox a écrit :
> On Wed, Nov 01, 2023 at 11:49:48AM +0100, Christophe JAILLET wrote:
>> If an load_nls_xxx() function fails a few lines above, the 'sbi->bdi_id' is
>> still 0.
>> So, in the error handling path, we will call ida_simple_remove(..., 0)
>> which is not allocated yet.
>>
>> In order to prevent a spurious "ida_free called for id=0 which is not
>> allocated." message, tweak the error handling path and add a new label.
> 
> That's not spurious!

My fault, as a non-native English speaking man.
I've always sought that spurious was meaning "odd" or "strange", but I 
was wrong :(

Here, a better wording could be "to prevent an un-expected "ida..."".
Is that ok for you?

Or the last sentence could shortened to only "In order to fix it, tweak 
the error handling path and add a new label.".

CJ

> You're freeing something that wasn't allocated.
> A good quality malloc allocation will warn you if you free() a random
> pointer.  I agree with everything abuot this patch (and the next) except
> for the changelog.
> 
>> Fixes: 0fd169576648 ("fs: Add VirtualBox guest shared folder (vboxsf) support")
>> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
>> ---
>>   fs/vboxsf/super.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/vboxsf/super.c b/fs/vboxsf/super.c
>> index 1fb8f4df60cb..9848af78215b 100644
>> --- a/fs/vboxsf/super.c
>> +++ b/fs/vboxsf/super.c
>> @@ -151,7 +151,7 @@ static int vboxsf_fill_super(struct super_block *sb, struct fs_context *fc)
>>   		if (!sbi->nls) {
>>   			vbg_err("vboxsf: Count not load '%s' nls\n", nls_name);
>>   			err = -EINVAL;
>> -			goto fail_free;
>> +			goto fail_destroy_idr;
>>   		}
>>   	}
>>   
>> @@ -224,6 +224,7 @@ static int vboxsf_fill_super(struct super_block *sb, struct fs_context *fc)
>>   		ida_simple_remove(&vboxsf_bdi_ida, sbi->bdi_id);
>>   	if (sbi->nls)
>>   		unload_nls(sbi->nls);
>> +fail_destroy_idr:
>>   	idr_destroy(&sbi->ino_idr);
>>   	kfree(sbi);
>>   	return err;
>> -- 
>> 2.34.1
>>
>>
> 
>