linux-kernel - Re: [PATCH] nilfs2: fix oops due to a bad aops initialization

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Message-ID: <4D931925.7020306@fusionio.com>
Date:	Wed, 30 Mar 2011 13:51:01 +0200
From:	Jens Axboe <jaxboe@...ionio.com>
To:	Ryusuke Konishi <konishi.ryusuke@....ntt.co.jp>
CC:	"linux-nilfs@...r.kernel.org" <linux-nilfs@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] nilfs2: fix oops due to a bad aops initialization

On 2011-03-30 13:48, Ryusuke Konishi wrote:
> On Wed, 30 Mar 2011 13:17:18 +0200, Jens Axboe wrote:
>> On 2011-03-30 13:07, Jens Axboe wrote:
>>> On 2011-03-30 06:25, Ryusuke Konishi wrote:
>>>> diff --git a/fs/nilfs2/page.c b/fs/nilfs2/page.c
>>>> index 4d2a1ee..9d2dc6b 100644
>>>> --- a/fs/nilfs2/page.c
>>>> +++ b/fs/nilfs2/page.c
>>>> @@ -495,12 +495,14 @@ unsigned nilfs_page_count_clean_buffers(struct page *page,
>>>>  void nilfs_mapping_init(struct address_space *mapping,
>>>>  			struct backing_dev_info *bdi)
>>>>  {
>>>> +	static const struct address_space_operations empty_aops;
>>>> +
>>>>  	mapping->host = NULL;
>>>>  	mapping->flags = 0;
>>>>  	mapping_set_gfp_mask(mapping, GFP_NOFS);
>>>>  	mapping->assoc_mapping = NULL;
>>>>  	mapping->backing_dev_info = bdi;
>>>> -	mapping->a_ops = NULL;
>>>> +	mapping->a_ops = &empty_aops;
>>>>  }
>>>
>>> Hmm wait, inode init should set the mapping aops to an empty type
>>> already. Does the OOPS go away if you just remove the mapping->a_ops =
>>> NULL assignment?
>>
>> In any case, I think this is a better fix.
>>
>> diff --git a/fs/inode.c b/fs/inode.c
>> index 5f4e11a..b818730 100644
>> --- a/fs/inode.c
>> +++ b/fs/inode.c
>> @@ -125,6 +125,13 @@ __cacheline_aligned_in_smp DEFINE_SPINLOCK(inode_wb_list_lock);
>>  static DECLARE_RWSEM(iprune_sem);
>>  
>>  /*
>> + * Empty aops. Can be used for the cases where the user does not
>> + * define any of the address_space operations.
>> + */
>> +const struct address_space_operations empty_aops = {
>> +};
>> +
>> +/*
>>   * Statistics gathering..
>>   */
>>  struct inodes_stat_t inodes_stat;
>> @@ -176,7 +183,6 @@ int proc_nr_inodes(ctl_table *table, int write,
>>   */
>>  int inode_init_always(struct super_block *sb, struct inode *inode)
>>  {
>> -	static const struct address_space_operations empty_aops;
>>  	static const struct inode_operations empty_iops;
>>  	static const struct file_operations empty_fops;
>>  	struct address_space *const mapping = &inode->i_data;
>> diff --git a/fs/nilfs2/page.c b/fs/nilfs2/page.c
>> index 4d2a1ee..1168059 100644
>> --- a/fs/nilfs2/page.c
>> +++ b/fs/nilfs2/page.c
>> @@ -500,7 +500,7 @@ void nilfs_mapping_init(struct address_space *mapping,
>>  	mapping_set_gfp_mask(mapping, GFP_NOFS);
>>  	mapping->assoc_mapping = NULL;
>>  	mapping->backing_dev_info = bdi;
>> -	mapping->a_ops = NULL;
>> +	mapping->a_ops = &empty_aops;
>>  }
>>  
>>  /*
>> diff --git a/fs/ubifs/xattr.c b/fs/ubifs/xattr.c
>> index c74400f..403c192 100644
>> --- a/fs/ubifs/xattr.c
>> +++ b/fs/ubifs/xattr.c
>> @@ -80,7 +80,6 @@ enum {
>>  };
>>  
>>  static const struct inode_operations none_inode_operations;
>> -static const struct address_space_operations none_address_operations;
>>  static const struct file_operations none_file_operations;
>>  
>>  /**
>> @@ -130,7 +129,7 @@ static int create_xattr(struct ubifs_info *c, struct inode *host,
>>  	}
>>  
>>  	/* Re-define all operations to be "nothing" */
>> -	inode->i_mapping->a_ops = &none_address_operations;
>> +	inode->i_mapping->a_ops = &empty_aops;
>>  	inode->i_op = &none_inode_operations;
>>  	inode->i_fop = &none_file_operations;
>>  
>> diff --git a/include/linux/fs.h b/include/linux/fs.h
>> index 52f283c..1b95af3 100644
>> --- a/include/linux/fs.h
>> +++ b/include/linux/fs.h
>> @@ -613,6 +613,8 @@ struct address_space_operations {
>>  	int (*error_remove_page)(struct address_space *, struct page *);
>>  };
>>  
>> +extern const struct address_space_operations empty_aops;
>> +
>>  /*
>>   * pagecache_write_begin/pagecache_write_end must be used by general code
>>   * to write into the pagecache.
>>
>> -- 
>> Jens Axboe
> 
> Sorry but I've already sent a pull request to Linus with your
> Acked-by.  And, this seems to be doing two things.  One is for fixing
> the current kerenl oops and another is for sharing the empty address
> space operations.
> 
> I have no problem with both patches, but for the purpose of the bug
> fix, the first one looks simpler.

No worries, I'll just merge later on.

-- 
Jens Axboe

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