linux-kernel - Re: [PATCH] fs: xfs: add NULL pointer check

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Message-ID: <222e0a61-d046-89fc-d46b-ac8da3ca7828@opensource.wdc.com>
Date:   Mon, 28 Mar 2022 13:07:58 +0900
From:   Damien Le Moal <damien.lemoal@...nsource.wdc.com>
To:     cgel.zte@...il.com, djwong@...nel.org
Cc:     linux-xfs@...r.kernel.org, dchinner@...hat.com,
        chandan.babu@...cle.com, bfoster@...hat.com,
        allison.henderson@...cle.com, lv.ruyi@....com.cn,
        linux-kernel@...r.kernel.org, Zeal Robot <zealci@....com.cn>
Subject: Re: [PATCH] fs: xfs: add NULL pointer check

On 3/28/22 12:40, Damien Le Moal wrote:
> On 3/28/22 12:26, cgel.zte@...il.com wrote:
>> From: Lv Ruyi <lv.ruyi@....com.cn>
>>
>> kmem_zalloc() is a memory allocation function which can return NULL when
>> some internal memory errors happen. It is safer to check NULL pointer.
>>
>> Reported-by: Zeal Robot <zealci@....com.cn>
>> Signed-off-by: Lv Ruyi <lv.ruyi@....com.cn>
>> ---
>>  fs/xfs/libxfs/xfs_attr_leaf.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/fs/xfs/libxfs/xfs_attr_leaf.c b/fs/xfs/libxfs/xfs_attr_leaf.c
>> index 014daa8c542d..e6694f49f563 100644
>> --- a/fs/xfs/libxfs/xfs_attr_leaf.c
>> +++ b/fs/xfs/libxfs/xfs_attr_leaf.c
>> @@ -1571,6 +1571,8 @@ xfs_attr3_leaf_compact(
>>  	trace_xfs_attr_leaf_compact(args);
>>  
>>  	tmpbuffer = kmem_alloc(args->geo->blksize, 0);
> 
> See kmem_alloc() code: this function cannot fail (it retries the
> allocation until success). So checking for NULL pointer does not make sense.

Note: this comment is not 100% correct. kmem_alloc() can fail if
KM_MAYFAIL is specified as a flag. But that is not the case here.

> 
>> +	if (!tmpbuffer)
>> +		return;
>>  	memcpy(tmpbuffer, bp->b_addr, args->geo->blksize);
>>  	memset(bp->b_addr, 0, args->geo->blksize);
>>  	leaf_src = (xfs_attr_leafblock_t *)tmpbuffer;
>> @@ -2290,6 +2292,8 @@ xfs_attr3_leaf_unbalance(
>>  		struct xfs_attr3_icleaf_hdr tmphdr;
>>  
>>  		tmp_leaf = kmem_zalloc(state->args->geo->blksize, 0);
>> +		if (!tmp_leaf)
>> +			return;
>>  
>>  		/*
>>  		 * Copy the header into the temp leaf so that all the stuff
> 
> 


-- 
Damien Le Moal
Western Digital Research