linux-ext4 - Re: [PATCH] ext4: memory leakage in ext4_discard

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Date:	Fri, 26 Mar 2010 22:12:08 +0800
From:	jing zhang <zj.barak@...il.com>
To:	"Aneesh Kumar K. V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	Andreas Dilger <adilger@....com>, tytso@....edu,
	linux-ext4 <linux-ext4@...r.kernel.org>,
	Dave Kleikamp <shaggy@...ux.vnet.ibm.com>
Subject: Re: [PATCH] ext4: memory leakage in ext4_discard_preallocations

2010/3/26, Aneesh Kumar K. V <aneesh.kumar@...ux.vnet.ibm.com>:
> On Sat, 20 Mar 2010 22:05:13 +0800, jing zhang <zj.barak@...il.com> wrote:
>>
>> Evening,
>>
>> Thanks Andreas and Ted for your good explanations to deal error in
>> gentle way, and I got it that the chance may exist since the pa is not
>> deleted from its group_list yet.
>>
>> And it also seems that there is work deserved.
>>        - zj
>>
>> ---
>>
>> --- linux-2.6.32/fs/ext4/mballoc.c	2009-12-03 11:51:22.000000000 +0800
>> +++ fs/mballoc.c	2010-03-20 21:40:04.000000000 +0800
>> @@ -3788,14 +3788,14 @@ repeat:
>>  		err = ext4_mb_load_buddy(sb, group, &e4b);
>>  		if (err) {
>>  			ext4_error(sb, __func__, "Error in loading buddy "
>> -					"information for %u", group);
>> +			"information for group %u inode %lu", group, inode->i_ino);
>>  			continue;
>>  		}
>>
>>  		bitmap_bh = ext4_read_block_bitmap(sb, group);
>>  		if (bitmap_bh == NULL) {
>>  			ext4_error(sb, __func__, "Error in reading block "
>> -					"bitmap for %u", group);
>> +			"bitmap for group %u inode %lu", group, inode->i_ino);
>>  			ext4_mb_release_desc(&e4b);
>>  			continue;
>>  		}
>> @@ -3811,6 +3811,14 @@ repeat:
>>  		list_del(&pa->u.pa_tmp_list);
>>  		call_rcu(&(pa)->u.pa_rcu, ext4_mb_pa_callback);
>>  	}
>> +	if (! list_empty(&list)) {
>> +		/*
>> +		 * we have to do something for the check in
>> +		 * the function, ext4_mb_discard_group_preallocations()
>> +		 */
>> +		list_for_each_entry(pa, &list, u.pa_tmp_list)
>> +			pa->pa_deleted = 0;
>> +	}
>>  	if (ac)
>>  		kmem_cache_free(ext4_ac_cachep, ac);
>>  }
>
> Can you add a comment saying if we fail to load buddy or read block
> bitmap we skip freeing the prealloc space. So mark it undeleted. The
> prealloc space is still removed from the inode but it is linked to the
> group prealloc list via (pa_group_list)
>
>
> -aneesh
>

/*
 * here the tricky is to mark PAs undeleted,
 * since they are still on their pa_group_list.
 */

That is it, Aneesh.

I am still waiting for comments, if any, from Ted, since I am not sure
the tricky is safe enough. And I am able not to deliver better patch
tonight :(

             - zj
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