[Ocfs2-devel] [PATCH V2] ocfs2: don't clear bh uptodate for block read

[Junxiao Bi]

Hi Changwei,

Thank you for the review.

See comment inlined

On 11/14/18 9:42 AM, Changwei Ge wrote:
> Hi Junxiao,
>
> Actually, I think we still have another race around reading blocks methods.
> Consider below scenario:
>
> Two parallel reading IO towards the same block.
> The first succeeds while the second fails.
> The second will clear _UPTODATE_ state in end_buffer_read_sync() thus making the first one failed as well.
>
> So better for us to not use generic end_buffer_read_sync() but ocfs2 own ones.

Is it necessary to do this complicated things? Seemed it will not cause 
any difference, at last IO error will be returned for this very block.

thanks,

Junxiao.

> But it has nothing to do with this patch.
> I am adding my Reviewed-by.
>
> Thanks,
> Changwei
>
> On 2018/11/14 8:04, Junxiao Bi wrote:
>> For sync io read in ocfs2_read_blocks_sync(), first clear bh uptodate flag
>> and submit the io, second wait io done, last check whether bh uptodate,
>> if not return io error.
>>
>> If two sync io for the same bh were issued, it could be the first io done
>> and set uptodate flag, but just before check that flag, the second io came
>> in and cleared uptodate, then ocfs2_read_blocks_sync() for the first io
>> will return IO error.
>>
>> Indeed it's not necessary to clear uptodate flag, as the io end handler
>> end_buffer_read_sync() will set or clear it based on io succeed or failed.
>>
>> The following message was found from a nfs server but the underlying
>> storage returned no error.
>>
>> [4106438.567376] (nfsd,7146,3):ocfs2_get_suballoc_slot_bit:2780 ERROR: read block 1238823695 failed -5
>> [4106438.567569] (nfsd,7146,3):ocfs2_get_suballoc_slot_bit:2812 ERROR: status = -5
>> [4106438.567611] (nfsd,7146,3):ocfs2_test_inode_bit:2894 ERROR: get alloc slot and bit failed -5
>> [4106438.567643] (nfsd,7146,3):ocfs2_test_inode_bit:2932 ERROR: status = -5
>> [4106438.567675] (nfsd,7146,3):ocfs2_get_dentry:94 ERROR: test inode bit failed -5
>>
>> Same issue in non sync read ocfs2_read_blocks(), fixed it as well.
>>
>> Signed-off-by: Junxiao Bi <junxiao.bi at oracle.com>
>> Cc: Changwei Ge <ge.changwei at h3c.com>
> Reviewed-by: Changwei Ge <ge.changwei at h3c.com>
>
>> ---
>>
>> v1 -> v2:
>>
>>     - fixed non sync read ocfs2_read_blocks() as well.
>>
>> ---
>>    fs/ocfs2/buffer_head_io.c | 2 --
>>    1 file changed, 2 deletions(-)
>>
>> diff --git a/fs/ocfs2/buffer_head_io.c b/fs/ocfs2/buffer_head_io.c
>> index 4ebbd57cbf84..f9b84f7a3e4b 100644
>> --- a/fs/ocfs2/buffer_head_io.c
>> +++ b/fs/ocfs2/buffer_head_io.c
>> @@ -161,7 +161,6 @@ int ocfs2_read_blocks_sync(struct ocfs2_super *osb, u64 block,
>>    #endif
>>    		}
>>    
>> -		clear_buffer_uptodate(bh);
>>    		get_bh(bh); /* for end_buffer_read_sync() */
>>    		bh->b_end_io = end_buffer_read_sync;
>>    		submit_bh(REQ_OP_READ, 0, bh);
>> @@ -341,7 +340,6 @@ int ocfs2_read_blocks(struct ocfs2_caching_info *ci, u64 block, int nr,
>>    				continue;
>>    			}
>>    
>> -			clear_buffer_uptodate(bh);
>>    			get_bh(bh); /* for end_buffer_read_sync() */
>>    			if (validate)
>>    				set_buffer_needs_validate(bh);
>>