On 2019/8/29 10:32, Darrick J. Wong wrote:
> On Tue, Aug 27, 2019 at 10:28:22AM +0800, kaixuxia wrote:
>>
>>
>> On 2019/8/27 10:13, Darrick J. Wong wrote:
>>> On Tue, Aug 27, 2019 at 10:07:43AM +0800, kaixuxia wrote:
>>>> On 2019/8/27 8:41, Darrick J. Wong wrote:
>>>>> On Sat, Aug 24, 2019 at 11:45:15AM +0800, kaixuxia wrote:
>>>>>> When performing rename operation with RENAME_WHITEOUT flag, we will
>>>>>> hold AGF lock to allocate or free extents in manipulating the dirents
>>>>>> firstly, and then doing the xfs_iunlink_remove() call last to hold
>>>>>> AGI lock to modify the tmpfile info, so we the lock order AGI->AGF.
>>>>>>
>>>>>> The big problem here is that we have an ordering constraint on AGF
>>>>>> and AGI locking - inode allocation locks the AGI, then can allocate
>>>>>> a new extent for new inodes, locking the AGF after the AGI. Hence
>>>>>> the ordering that is imposed by other parts of the code is AGI before
>>>>>> AGF. So we get an ABBA deadlock between the AGI and AGF here.
>>>>>>
>>>>>> Process A:
>>>>>> Call trace:
>>>>>> ? __schedule+0x2bd/0x620
>>>>>> schedule+0x33/0x90
>>>>>> schedule_timeout+0x17d/0x290
>>>>>> __down_common+0xef/0x125
>>>>>> ? xfs_buf_find+0x215/0x6c0 [xfs]
>>>>>> down+0x3b/0x50
>>>>>> xfs_buf_lock+0x34/0xf0 [xfs]
>>>>>> xfs_buf_find+0x215/0x6c0 [xfs]
>>>>>> xfs_buf_get_map+0x37/0x230 [xfs]
>>>>>> xfs_buf_read_map+0x29/0x190 [xfs]
>>>>>> xfs_trans_read_buf_map+0x13d/0x520 [xfs]
>>>>>> xfs_read_agf+0xa6/0x180 [xfs]
>>>>>> ? schedule_timeout+0x17d/0x290
>>>>>> xfs_alloc_read_agf+0x52/0x1f0 [xfs]
>>>>>> xfs_alloc_fix_freelist+0x432/0x590 [xfs]
>>>>>> ? down+0x3b/0x50
>>>>>> ? xfs_buf_lock+0x34/0xf0 [xfs]
>>>>>> ? xfs_buf_find+0x215/0x6c0 [xfs]
>>>>>> xfs_alloc_vextent+0x301/0x6c0 [xfs]
>>>>>> xfs_ialloc_ag_alloc+0x182/0x700 [xfs]
>>>>>> ? _xfs_trans_bjoin+0x72/0xf0 [xfs]
>>>>>> xfs_dialloc+0x116/0x290 [xfs]
>>>>>> xfs_ialloc+0x6d/0x5e0 [xfs]
>>>>>> ? xfs_log_reserve+0x165/0x280 [xfs]
>>>>>> xfs_dir_ialloc+0x8c/0x240 [xfs]
>>>>>> xfs_create+0x35a/0x610 [xfs]
>>>>>> xfs_generic_create+0x1f1/0x2f0 [xfs]
>>>>>> ...
>>>>>>
>>>>>> Process B:
>>>>>> Call trace:
>>>>>> ? __schedule+0x2bd/0x620
>>>>>> ? xfs_bmapi_allocate+0x245/0x380 [xfs]
>>>>>> schedule+0x33/0x90
>>>>>> schedule_timeout+0x17d/0x290
>>>>>> ? xfs_buf_find+0x1fd/0x6c0 [xfs]
>>>>>> __down_common+0xef/0x125
>>>>>> ? xfs_buf_get_map+0x37/0x230 [xfs]
>>>>>> ? xfs_buf_find+0x215/0x6c0 [xfs]
>>>>>> down+0x3b/0x50
>>>>>> xfs_buf_lock+0x34/0xf0 [xfs]
>>>>>> xfs_buf_find+0x215/0x6c0 [xfs]
>>>>>> xfs_buf_get_map+0x37/0x230 [xfs]
>>>>>> xfs_buf_read_map+0x29/0x190 [xfs]
>>>>>> xfs_trans_read_buf_map+0x13d/0x520 [xfs]
>>>>>> xfs_read_agi+0xa8/0x160 [xfs]
>>>>>> xfs_iunlink_remove+0x6f/0x2a0 [xfs]
>>>>>> ? current_time+0x46/0x80
>>>>>> ? xfs_trans_ichgtime+0x39/0xb0 [xfs]
>>>>>> xfs_rename+0x57a/0xae0 [xfs]
>>>>>> xfs_vn_rename+0xe4/0x150 [xfs]
>>>>>> ...
>>>>>>
>>>>>> In this patch we move the xfs_iunlink_remove() call to
>>>>>> before acquiring the AGF lock to preserve correct AGI/AGF locking
>>>>>> order.
>>>>>>
>>>>>> Signed-off-by: kaixuxia <kaixuxia@xxxxxxxxxxx>
>>>>>> Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx>
>>>>>> ---
>>>>>> fs/xfs/xfs_inode.c | 83 +++++++++++++++++++++++++++---------------------------
>>>>>> 1 file changed, 42 insertions(+), 41 deletions(-)
>>>>>>
>>>>>> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
>>>>>> index 6467d5e..8ffd44f 100644
>>>>>> --- a/fs/xfs/xfs_inode.c
>>>>>> +++ b/fs/xfs/xfs_inode.c
>>>>>> @@ -3282,7 +3282,8 @@ struct xfs_iunlink {
>>>>>> spaceres);
>>>>>>
>>>>>> /*
>>>>>> - * Set up the target.
>>>>>> + * Check for expected errors before we dirty the transaction
>>>>>> + * so we can return an error without a transaction abort.
>>>>>> */
>>>>>> if (target_ip == NULL) {
>>>>>> /*
>>>>>> @@ -3294,6 +3295,46 @@ struct xfs_iunlink {
>>>>>> if (error)
>>>>>> goto out_trans_cancel;
>>>>>> }
>>>>>> + } else {
>>>>>> + /*
>>>>>> + * If target exists and it's a directory, check that whether
>>>>>> + * it can be destroyed.
>>>>>> + */
>>>>>> + if (S_ISDIR(VFS_I(target_ip)->i_mode) &&
>>>>>> + (!xfs_dir_isempty(target_ip) ||
>>>>>> + (VFS_I(target_ip)->i_nlink > 2))) {
>>>>>> + error = -EEXIST;
>>>>>> + goto out_trans_cancel;
>>>>>> + }
>>>>>> + }
>>>>>> +
>>>>>> + /*
>>>>>> + * Directory entry creation below may acquire the AGF. Remove
>>>>>> + * the whiteout from the unlinked list first to preserve correct
>>>>>> + * AGI/AGF locking order. This dirties the transaction so failures
>>>>>> + * after this point will abort and log recovery will clean up the
>>>>>> + * mess.
>>>>>> + *
>>>>>> + * For whiteouts, we need to bump the link count on the whiteout
>>>>>> + * inode. After this point, we have a real link, clear the tmpfile
>>>>>> + * state flag from the inode so it doesn't accidentally get misused
>>>>>> + * in future.
>>>>>> + */
>>>>>> + if (wip) {
>>>>>> + ASSERT(VFS_I(wip)->i_nlink == 0);
>>>>>> + error = xfs_iunlink_remove(tp, wip);
>>>>>> + if (error)
>>>>>> + goto out_trans_cancel;
>>>>>> +
>>>>>> + xfs_bumplink(tp, wip);
>>>>>> + xfs_trans_log_inode(tp, wip, XFS_ILOG_CORE);
>>>>>> + VFS_I(wip)->i_state &= ~I_LINKABLE;
>>>>>> + }
>>>>>> +
>>>>>> + /*
>>>>>> + * Set up the target.
>>>>>> + */
>>>>>> + if (target_ip == NULL) {
>>>>>> /*
>>>>>> * If target does not exist and the rename crosses
>>>>>> * directories, adjust the target directory link count
>>>>>> @@ -3312,22 +3353,6 @@ struct xfs_iunlink {
>>>>>> }
>>>>>> } else { /* target_ip != NULL */
>>>>>> /*
>>>>>> - * If target exists and it's a directory, check that both
>>>>>> - * target and source are directories and that target can be
>>>>>> - * destroyed, or that neither is a directory.
>>>>>> - */
>>>>>> - if (S_ISDIR(VFS_I(target_ip)->i_mode)) {
>>>>>> - /*
>>>>>> - * Make sure target dir is empty.
>>>>>> - */
>>>>>> - if (!(xfs_dir_isempty(target_ip)) ||
>>>>>> - (VFS_I(target_ip)->i_nlink > 2)) {
>>>>>> - error = -EEXIST;
>>>>>> - goto out_trans_cancel;
>>>>>> - }
>>>>>> - }
>>>>>> -
>>>>>> - /*
>>>>>> * Link the source inode under the target name.
>>>>>> * If the source inode is a directory and we are moving
>>>>>> * it across directories, its ".." entry will be
>>>>>
>>>>> ...will be replaced and then we droplink the target_ip.
>>>>>
>>>>> Question: Will we have the same ABBA deadlock potential here if we have
>>>>> to allocate a block from AG 2 to hold the directory entry, but then we
>>>>> drop target_ip onto the unlinked list, and target_ip was also from AG 2?
>>>>> We also have to lock the AGI to put things on the unlinked list.
>>>>>
>>>>> Granted, that's a slightly different use case, but they seem related...
>>>>
>>>> Right, we will have the ABBA deadlock here if we have to allocate the
>>>> block fist and then put the target_ip on the unlinked list. Of course,
>>>> we need to fix it, but these two deadlock problems have different use
>>>> case and different reasons, maybe it's better that we fix them with
>>>> different patches, and then the subject of this patch need to be
>>>> changed...
>>>> I also can send another patch to fix the new deadlock problem.
>>>
>>> Ok. By the way, do you have a quick reproducer that we can put into
>>> xfstests?
>>
>> Yeah, I have a quick reproducer that mkfs.xfs the disk with agcount=1
>> or agcount=2, and I can send the testcase to xfstests.
>>
>> In a word, I will send two patches to fix the different deadlock
>> problems, and then the corresponding quick reproducers will also
>> be sent later.
>
> Er... did you send the second patch to fix the droplink deadlock? Or
> the reproducers?
Yeah, they are on the way.
By the way, the second patch to fix the droplink deadlock will be
a separate patch that not contains this iunlink_remove() deadlock
patch because they have different use and different reasons, so
I'm worry about that this patch will be forget after that, so
send a ping...
For the reproducers, the original testcase will cost about ten
minutes to reproduce the problem, so I am trying to reduce this
time and send it when done.
>
> --D
>
>>> --D
>>>
>>>>
>>>>>
>>>>> --D
>>>>>
>>>>>> @@ -3417,30 +3442,6 @@ struct xfs_iunlink {
>>>>>> if (error)
>>>>>> goto out_trans_cancel;
>>>>>>
>>>>>> - /*
>>>>>> - * For whiteouts, we need to bump the link count on the whiteout inode.
>>>>>> - * This means that failures all the way up to this point leave the inode
>>>>>> - * on the unlinked list and so cleanup is a simple matter of dropping
>>>>>> - * the remaining reference to it. If we fail here after bumping the link
>>>>>> - * count, we're shutting down the filesystem so we'll never see the
>>>>>> - * intermediate state on disk.
>>>>>> - */
>>>>>> - if (wip) {
>>>>>> - ASSERT(VFS_I(wip)->i_nlink == 0);
>>>>>> - xfs_bumplink(tp, wip);
>>>>>> - error = xfs_iunlink_remove(tp, wip);
>>>>>> - if (error)
>>>>>> - goto out_trans_cancel;
>>>>>> - xfs_trans_log_inode(tp, wip, XFS_ILOG_CORE);
>>>>>> -
>>>>>> - /*
>>>>>> - * Now we have a real link, clear the "I'm a tmpfile" state
>>>>>> - * flag from the inode so it doesn't accidentally get misused in
>>>>>> - * future.
>>>>>> - */
>>>>>> - VFS_I(wip)->i_state &= ~I_LINKABLE;
>>>>>> - }
>>>>>> -
>>>>>> xfs_trans_ichgtime(tp, src_dp, XFS_ICHGTIME_MOD | XFS_ICHGTIME_CHG);
>>>>>> xfs_trans_log_inode(tp, src_dp, XFS_ILOG_CORE);
>>>>>> if (new_parent)
>>>>>> --
>>>>>> 1.8.3.1
>>>>>>
>>>>>> --
>>>>>> kaixuxia
>>>>
>>>> --
>>>> kaixuxia
>>
>> --
>> kaixuxia
--
kaixuxia
