linux-kernel - Re: [PATCH V3 1/2] xfs: Fix the owner setting issue for rmap query in xfs fsmap

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Message-ID: <768dd909-c77c-4655-af01-5aa064ea9477@huawei.com>
Date: Fri, 16 Aug 2024 09:02:52 +0800
From: Zizhi Wo <wozizhi@...wei.com>
To: "Darrick J. Wong" <djwong@...nel.org>
CC: <chandan.babu@...cle.com>, <dchinner@...hat.com>, <osandov@...com>,
	<john.g.garry@...cle.com>, <linux-xfs@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <yangerkun@...wei.com>
Subject: Re: [PATCH V3 1/2] xfs: Fix the owner setting issue for rmap query in
 xfs fsmap



在 2024/8/16 0:36, Darrick J. Wong 写道:
> On Mon, Aug 12, 2024 at 09:15:04AM +0800, Zizhi Wo wrote:
>> I notice a rmap query bug in xfs_io fsmap:
>> [root@...ora ~]# xfs_io -c 'fsmap -vvvv' /mnt
>>   EXT: DEV    BLOCK-RANGE           OWNER              FILE-OFFSET      AG AG-OFFSET             TOTAL
>>     0: 253:16 [0..7]:               static fs metadata                  0  (0..7)                    8
>>     1: 253:16 [8..23]:              per-AG metadata                     0  (8..23)                  16
>>     2: 253:16 [24..39]:             inode btree                         0  (24..39)                 16
>>     3: 253:16 [40..47]:             per-AG metadata                     0  (40..47)                  8
>>     4: 253:16 [48..55]:             refcount btree                      0  (48..55)                  8
>>     5: 253:16 [56..103]:            per-AG metadata                     0  (56..103)                48
>>     6: 253:16 [104..127]:           free space                          0  (104..127)               24
>>     ......
>>
>> Bug:
>> [root@...ora ~]# xfs_io -c 'fsmap -vvvv -d 0 3' /mnt
>> [root@...ora ~]#
>> Normally, we should be able to get one record, but we got nothing.
>>
>> The root cause of this problem lies in the incorrect setting of rm_owner in
>> the rmap query. In the case of the initial query where the owner is not
>> set, __xfs_getfsmap_datadev() first sets info->high.rm_owner to ULLONG_MAX.
>> This is done to prevent any omissions when comparing rmap items. However,
>> if the current ag is detected to be the last one, the function sets info's
>> high_irec based on the provided key. If high->rm_owner is not specified, it
>> should continue to be set to ULLONG_MAX; otherwise, there will be issues
>> with interval omissions. For example, consider "start" and "end" within the
>> same block. If high->rm_owner == 0, it will be smaller than the founded
>> record in rmapbt, resulting in a query with no records. The main call stack
>> is as follows:
>>
>> xfs_ioc_getfsmap
>>    xfs_getfsmap
>>      xfs_getfsmap_datadev_rmapbt
>>        __xfs_getfsmap_datadev
>>          info->high.rm_owner = ULLONG_MAX
>>          if (pag->pag_agno == end_ag)
>> 	  xfs_fsmap_owner_to_rmap
>> 	    // set info->high.rm_owner = 0 because fmr_owner == 0
>> 	    dest->rm_owner = 0
>> 	// get nothing
>> 	xfs_getfsmap_datadev_rmapbt_query
>>
>> The problem can be resolved by setting the rm_owner of high to ULLONG_MAX
>> again under certain conditions.
>>
>> After applying this patch, the above problem have been solved:
>> [root@...ora ~]# xfs_io -c 'fsmap -vvvv -d 0 3' /mnt
>>   EXT: DEV    BLOCK-RANGE      OWNER              FILE-OFFSET      AG AG-OFFSET        TOTAL
>>     0: 253:16 [0..7]:          static fs metadata                  0  (0..7)               8
>>
>> Fixes: e89c041338ed ("xfs: implement the GETFSMAP ioctl")
>> Signed-off-by: Zizhi Wo <wozizhi@...wei.com>
>> ---
>>   fs/xfs/xfs_fsmap.c | 7 +++++++
>>   1 file changed, 7 insertions(+)
>>
>> diff --git a/fs/xfs/xfs_fsmap.c b/fs/xfs/xfs_fsmap.c
>> index 85dbb46452ca..d346acff7725 100644
>> --- a/fs/xfs/xfs_fsmap.c
>> +++ b/fs/xfs/xfs_fsmap.c
>> @@ -655,6 +655,13 @@ __xfs_getfsmap_datadev(
>>   			error = xfs_fsmap_owner_to_rmap(&info->high, &keys[1]);
>>   			if (error)
>>   				break;
>> +			/*
>> +			 * Set the owner of high_key to the maximum again to
>> +			 * prevent missing intervals during the query.
>> +			 */
>> +			if (info->high.rm_owner == 0 &&
>> +			    info->missing_owner == XFS_FMR_OWN_FREE)
>> +			    info->high.rm_owner = ULLONG_MAX;
> 
> Shouldn't this be in xfs_fsmap_owner_to_rmap?
> 
> And, looking at that function, isn't this the solution:
> 
> 	switch (src->fmr_owner) {
> 	case 0:			/* "lowest owner id possible" */
> 	case -1ULL:		/* "highest owner id possible" */
> 		dest->rm_owner = src->fmr_owner;
> 		break;
> 

Yes, the simple modification logic in the xfs_fsmap_owner_to_rmap
function makes more sense.

Thanks,
Zizhi Wo

> instead of this special-casing outside the setter function?
> 
> --D
> 
>>   			xfs_getfsmap_set_irec_flags(&info->high, &keys[1]);
>>   		}
>>   
>> -- 
>> 2.39.2
>>
>>
>