Re: bcache detach lead to xfs force shutdown

[Zhang Zhen <zhangzhen.email@gmail.com>]

On 3/2/22 5:19 PM, Coly Li wrote:
> On 2/23/22 8:26 PM, Zhang Zhen wrote:
>>
>> 在 2022/2/23 下午5:03, Coly Li 写道:
>>> On 2/21/22 5:33 PM, Zhang Zhen wrote:
>>>> Hi coly，
>>>>
>>>> We encounted a bcache detach problem, during the io process，the 
>>>> cache device become missing.
>>>>
>>>> The io error status returned to xfs， and in some case， the xfs do 
>>>> force shutdown.
>>>>
>>>> The dmesg as follows:
>>>> Feb  2 20:59:23  kernel: bcache: bch_count_io_errors() nvme0n1p56: 
>>>> IO error on writing btree.
>>>> Feb  2 20:59:23  kernel: bcache: bch_count_io_errors() nvme0n1p44: 
>>>> IO error on writing btree.
>>>> Feb  2 20:59:23  kernel: bcache: bch_count_io_errors() nvme0n1p44: 
>>>> IO error on writing btree.
>>>> Feb  2 20:59:23  kernel: bcache: bch_count_io_errors() nvme0n1p57: 
>>>> IO error on writing btree.
>>>> Feb  2 20:59:23  kernel: bcache: bch_count_io_errors() nvme0n1p56: 
>>>> IO error on writing btree.
>>>> Feb  2 20:59:23  kernel: bcache: bch_count_io_errors() nvme0n1p57: 
>>>> IO error on writing btree.
>>>> Feb  2 20:59:23  kernel: bcache: bch_count_io_errors() nvme0n1p56: 
>>>> IO error on writing btree.
>>>> Feb  2 20:59:23  kernel: bcache: bch_btree_insert() error -5
>>>> Feb  2 20:59:23  kernel: XFS (bcache43): metadata I/O error in 
>>>> "xfs_buf_iodone_callback_error" at daddr 0x80034658 len 32 error 12
>>>> Feb  2 20:59:23  kernel: bcache: bch_btree_insert() error -5
>>>> Feb  2 20:59:23  kernel: bcache: bch_btree_insert() error -5
>>>> Feb  2 20:59:23  kernel: bcache: bch_btree_insert() error -5
>>>> Feb  2 20:59:23  kernel: bcache: bch_btree_insert() error -5
>>>> Feb  2 20:59:23  kernel: bcache: bch_cache_set_error() bcache: error 
>>>> on 004f8aa7-561a-4ba7-bf7b-292e461d3f18:
>>>> Feb  2 20:59:23  kernel: journal io error
>>>> Feb  2 20:59:23  kernel: bcache: bch_cache_set_error() , disabling 
>>>> caching
>>>> Feb  2 20:59:23  kernel: bcache: bch_btree_insert() error -5
>>>> Feb  2 20:59:23  kernel: bcache: conditional_stop_bcache_device() 
>>>> stop_when_cache_set_failed of bcache43 is "auto" and cache is clean, 
>>>> keep it alive.
>>>> Feb  2 20:59:23  kernel: XFS (bcache43): metadata I/O error in 
>>>> "xlog_iodone" at daddr 0x400123e60 len 64 error 12
>>>> Feb  2 20:59:23  kernel: XFS (bcache43): xfs_do_force_shutdown(0x2) 
>>>> called from line 1298 of file fs/xfs/xfs_log.c. Return address = 
>>>> 00000000c1c8077f
>>>> Feb  2 20:59:23  kernel: XFS (bcache43): Log I/O Error Detected. 
>>>> Shutting down filesystem
>>>> Feb  2 20:59:23  kernel: XFS (bcache43): Please unmount the 
>>>> filesystem and rectify the problem(s)
>>>>
>>>>
>>>> We checked the code, the error status is returned in 
>>>> cached_dev_make_request and closure_bio_submit function.
>>>>
>>>> 1180 static blk_qc_t cached_dev_make_request(struct request_queue *q,
>>>> 1181                     struct bio *bio)
>>>> 1182 {
>>>> 1183     struct search *s;
>>>> 1184     struct bcache_device *d = bio->bi_disk->private_data;
>>>> 1185     struct cached_dev *dc = container_of(d, struct cached_dev, 
>>>> disk);
>>>> 1186     int rw = bio_data_dir(bio);
>>>> 1187
>>>> 1188     if (unlikely((d->c && test_bit(CACHE_SET_IO_DISABLE, 
>>>> &d->c->flags)) ||
>>>> 1189              dc->io_disable)) {
>>>> 1190         bio->bi_status = BLK_STS_IOERR;
>>>> 1191         bio_endio(bio);
>>>> 1192         return BLK_QC_T_NONE;
>>>> 1193     }
>>>>
>>>>  901 static inline void closure_bio_submit(struct cache_set *c,
>>>>  902                       struct bio *bio,
>>>>  903                       struct closure *cl)
>>>>  904 {
>>>>  905     closure_get(cl);
>>>>  906     if (unlikely(test_bit(CACHE_SET_IO_DISABLE, &c->flags))) {
>>>>  907         bio->bi_status = BLK_STS_IOERR;
>>>>  908         bio_endio(bio);
>>>>  909         return;
>>>>  910     }
>>>>  911     generic_make_request(bio);
>>>>  912 }
>>>>
>>>> Can the cache set detached and don't return error status to fs?
>>>
>>>
>>> Hi Zhang,
>>>
>>>
>>> What is your kernel version and where do you get the kernel?
>>> My kernel version is 4.18 of Centos.
>> The code of this part is same with upstream kernel.
>>> It seems like an as designed behavior, could you please describe more 
>>> detail about the operation sequence?
>>>
>> Yes, i think so too.
>> The reproduce opreation as follows:
>> 1. mount a bcache disk with xfs
>>
>> /dev/bcache1 on /media/disk1 type xfs
>>
>> 2. run ls in background
>> #!/bin/bash
>>
>> while true
>> do
>>   echo 2 > /proc/sys/vm/drop_caches
>>   ls -R /media/disk1 > /dev/null
>> done
>>
>>
>> 3. remove cache disk sdc
>> echo 1 >/sys/block/sdc/device/delete
>>
>> 4. dmesg should get xfs error
>>
>> I write a patch to improve，please help to review it, thanks.

> 
> Hold on. Why do you think it should be fixed? As I said, it is 
> as-designed behavior.
> 
We use bcache in writearound mode, just cache read io.
Currently, bcache return io error during detach, randomly lead to
xfs force shutdown.

After bcache auto detach finished, some dir read write normaly, but
the others can't read write because of xfs force shutdown.
This inconsistency confuses filesystem users.

Thanks.
> 
> Coly Li
>