On 03/21/2013 01:44 PM, Dave Chinner wrote:
> On Thu, Mar 21, 2013 at 12:12:51PM +0800, Jeff Liu wrote:
>> In growfs operation, the unused parts of superblocks in the latest old AG are
>> zero filled, hence we can safely read the secondary superblock buffer of it
>> rather than getting a new buffer for it again.
>
> From the code:
>
> oagcount = mp->m_sb.sb_agcount;
>
> And because the AG indexes are zero numbered, the index of the
> last original AGs is (oagcount - 1). Hence we shoul donly be reading
> from the AG headers if the current AG index is less than oagcount.
>
>> This is a small refinement for commits 1375cb65.
>>
>> Cc: Dave Chinner <david@xxxxxxxxxxxxx>
>> Signed-off-by: Jie Liu <jeff.liu@xxxxxxxxxx>
>> ---
>> fs/xfs/xfs_fsops.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
>> index 94eaeed..7d435dd 100644
>> --- a/fs/xfs/xfs_fsops.c
>> +++ b/fs/xfs/xfs_fsops.c
>> @@ -449,7 +449,7 @@ xfs_growfs_data_private(
>> * disk as the contents of the new area we are growing into is
>> * completely unknown.
>> */
>> - if (agno < oagcount) {
>> + if (agno <= oagcount) {
>
> With this change, when agno == oagcount we are one AG beyond the
> original filesystem size and so if we read that space, we are
> reading uninitialised data.
>
> AFAICT, the current code is correct...
Oops, I made a stupid mistake. The index of the
last original AGs is (oagcount - 1) rather than oagcount...
Sorry for the noise!
Thanks,
-Jeff
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