From: Badari Pulavarty <pbadari@us.ibm.com>
Subject: Re: BUG: warning at fs/ext3/inode.c:1016/ext3_getblk()
Date: Tue, 05 Sep 2006 13:14:01 -0700
Message-ID: <44FDDA89.7080207@us.ibm.com>
References: <20060905171049.GB27433@ele.uri.edu>	 <1157479756.23501.18.camel@dyn9047017100.beaverton.ibm.com> <1157482632.19432.6.camel@kleikamp.austin.ibm.com>
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Cc: Badari Pulavarty <pbadari@gmail.com>,
	Will Simoneau <simoneau@ele.uri.edu>,
	lkml <linux-kernel@vger.kernel.org>,
	ext4 <linux-ext4@vger.kernel.org>
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To: Dave Kleikamp <shaggy@austin.ibm.com>
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Dave Kleikamp wrote:
> On Tue, 2006-09-05 at 11:09 -0700, Badari Pulavarty wrote:
>   
>> On Tue, 2006-09-05 at 13:10 -0400, Will Simoneau wrote:
>>     
>>> Has anyone seen this before? These three traces occured at different times
>>> today when three new user accounts (and associated quotas) were created. This
>>> machine is an NFS server which uses quotas on an ext3 fs (dir_index is on).
>>> Kernel is 2.6.17.11 on an x86 smp w/64G highmem; 4G ram is installed. The
>>> affected filesystem is on a software raid1 of two hardware raid0 volumes from a
>>> megaraid card.
>>>
>>> BUG: warning at fs/ext3/inode.c:1016/ext3_getblk()
>>>  <c01c5140> ext3_getblk+0x98/0x2a6  <c03b2806> md_wakeup_thread+0x26/0x2a
>>>  <c01c536d> ext3_bread+0x1f/0x88  <c01cedf9> ext3_quota_read+0x136/0x1ae
>>>  <c018b683> v1_read_dqblk+0x61/0xac  <c0188f32> dquot_acquire+0xf6/0x107
>>>  <c01ceaba> ext3_acquire_dquot+0x46/0x68  <c01897d4> dqget+0x155/0x1e7
>>>  <c018a97b> dquot_transfer+0x3e0/0x3e9  <c016fe52> dput+0x23/0x13e
>>>  <c01c7986> ext3_setattr+0xc3/0x240  <c0120f66> current_fs_time+0x52/0x6a
>>>  <c017320e> notify_change+0x2bd/0x30d  <c0159246> chown_common+0x9c/0xc5
>>>  <c02a222c> strncpy_from_user+0x3b/0x68  <c0167fe6> do_path_lookup+0xdf/0x266
>>>  <c016841b> __user_walk_fd+0x44/0x5a  <c01592b9> sys_chown+0x4a/0x55
>>>  <c015a43c> vfs_write+0xe7/0x13c  <c01695d4> sys_mkdir+0x1f/0x23
>>>  <c0102a97> syscall_call+0x7/0xb 
>>>       
>> I think its a bogus warning. 
>>
>> ext3_getblk() is calling ext3_get_blocks_handle() to map "1" block for
>> read. But for *some* reason ext3_get_blocks_handle() more than 1 block.
>> ext3_get_blocks_handle() return "positive #of blocks" is a valid case.
>> So needs to be fixed.
>>     
>
> I'm having a hard time figuring out exactly what ext3_get_blocks_handle
> is trying to return, but it looks to me like if it is allocating one
> data block, and needs to allocate an indirect block as well, then it
> will return 2 rather than 1.  Is this expected, or am I just confused?
>
>   

It would return "1" in that case.. (data block)

 > 0 means get_block() suceeded and indicates the number of blocks mapped
= 0 lookup failed
< 0 mean error case

>> I did search for callers of ext3_get_blocks_handle() and found that
>> ext3_readdir() seems to do wrong thing all the time with error check :(
>> Need to take a closer look..
>>
>> 	err = ext3_get_blocks_handle(NULL, inode, blk, 1,
>>                                                 &map_bh, 0, 0);
>>         if (err > 0) {  <<<< BAD
>>                   page_cache_readahead(sb->s_bdev->bd_inode->i_mapping,
>>                                 &filp->f_ra,
>>                                 filp,
>>                                 map_bh.b_blocknr >>
>>                                 (PAGE_CACHE_SHIFT - inode->i_blkbits),
>>                                 1);
>>                         bh = ext3_bread(NULL, inode, blk, 0, &err);
>>        }
>>     
>
> Bad to do this what it's doing, or bad to call name the variable "err"?
> I think if it looked like this:
>
> 	count = ext3_get_blocks_handle(NULL, inode, blk, 1,
>                                                 &map_bh, 0, 0);
>         if (count > 0) { 
>
> it would be a lot less confusing.
>   
I am sorry !! it is doing the right thing :(


Thanks,
Badari