[PATCH] Bcache: don't return BLK_STS_IOERR during cache detach

[PATCH] Bcache: don't return BLK_STS_IOERR during cache detach

[Zhang Zhen]

Before this patch, if cache device missing, cached_dev_submit_bio return 
io err
to fs during cache detach, randomly lead to xfs do force shutdown.

This patch delay the cache io submit in cached_dev_submit_bio
and wait for cache set detach finish.
So if the cache device become missing, bcache detach cache set 
automatically,
and the io will sumbit normally.

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)

Signed-off-by: Zhen Zhang <zhangzhen.email@gmail.com>
---
  drivers/md/bcache/bcache.h  | 5 -----
  drivers/md/bcache/request.c | 8 ++++----
  drivers/md/bcache/super.c   | 3 ++-
  3 files changed, 6 insertions(+), 10 deletions(-)

diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
index 9ed9c955add7..e5227dd08e3a 100644
--- a/drivers/md/bcache/bcache.h
+++ b/drivers/md/bcache/bcache.h
@@ -928,11 +928,6 @@ static inline void closure_bio_submit(struct 
cache_set *c,
  				      struct closure *cl)
  {
  	closure_get(cl);
-	if (unlikely(test_bit(CACHE_SET_IO_DISABLE, &c->flags))) {
-		bio->bi_status = BLK_STS_IOERR;
-		bio_endio(bio);
-		return;
-	}
  	submit_bio_noacct(bio);
  }
  diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
index d15aae6c51c1..36f0ee95b51f 100644
--- a/drivers/md/bcache/request.c
+++ b/drivers/md/bcache/request.c
@@ -13,6 +13,7 @@
  #include "request.h"
  #include "writeback.h"
  +#include <linux/delay.h>
  #include <linux/module.h>
  #include <linux/hash.h>
  #include <linux/random.h>
@@ -1172,11 +1173,10 @@ void cached_dev_submit_bio(struct bio *bio)
  	unsigned long start_time;
  	int rw = bio_data_dir(bio);
  -	if (unlikely((d->c && test_bit(CACHE_SET_IO_DISABLE, &d->c->flags)) ||
+	while (unlikely((d->c && test_bit(CACHE_SET_IO_DISABLE, &d->c->flags)) ||
  		     dc->io_disable)) {
-		bio->bi_status = BLK_STS_IOERR;
-		bio_endio(bio);
-		return;
+		/* wait for detach finish and d->c == NULL. */
+		msleep(2);
  	}
   	if (likely(d->c)) {
diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 140f35dc0c45..8d9a5e937bc8 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -661,7 +661,8 @@ int bch_prio_write(struct cache *ca, bool wait)
  		p->csum		= bch_crc64(&p->magic, meta_bucket_bytes(&ca->sb) - 8);
   		bucket = bch_bucket_alloc(ca, RESERVE_PRIO, wait);
-		BUG_ON(bucket == -1);
+		if (bucket == -1)
+			return -1;
   		mutex_unlock(&ca->set->bucket_lock);
  		prio_io(ca, bucket, REQ_OP_WRITE, 0);
-- 
2.25.1

Re: [PATCH] Bcache: don't return BLK_STS_IOERR during cache detach

[Coly Li]

On 3/10/22 10:50 AM, Zhang Zhen wrote:
> Before this patch, if cache device missing, cached_dev_submit_bio 
> return io err
> to fs during cache detach, randomly lead to xfs do force shutdown.
>
> This patch delay the cache io submit in cached_dev_submit_bio
> and wait for cache set detach finish.
> So if the cache device become missing, bcache detach cache set 
> automatically,
> and the io will sumbit normally.
>
> 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)
>
> Signed-off-by: Zhen Zhang <zhangzhen.email@gmail.com>
> ---
>  drivers/md/bcache/bcache.h  | 5 -----
>  drivers/md/bcache/request.c | 8 ++++----
>  drivers/md/bcache/super.c   | 3 ++-
>  3 files changed, 6 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
> index 9ed9c955add7..e5227dd08e3a 100644
> --- a/drivers/md/bcache/bcache.h
> +++ b/drivers/md/bcache/bcache.h
> @@ -928,11 +928,6 @@ static inline void closure_bio_submit(struct 
> cache_set *c,
>                        struct closure *cl)
>  {
>      closure_get(cl);
> -    if (unlikely(test_bit(CACHE_SET_IO_DISABLE, &c->flags))) {
> -        bio->bi_status = BLK_STS_IOERR;
> -        bio_endio(bio);
> -        return;
> -    }
>      submit_bio_noacct(bio);
>  }


Comparing to make bcache device living as it looks like, avoiding data 
corruption or stale is much more critical. Therefore once there is 
critical device failure detected, the following I/O requests must be 
stopped (especially write request) to avoid further data corruption. 
Without the above checking for CACHE_SET_IO_DISABLE, the cache has to be 
attached until there is no I/O. For a busy system it should be quite 
long time. Then users may encounter silent data corruption or 
inconsistency after a long time since hardware failed.


Again, with the above change, you may introduce other issue which more 
hard to detect.


>  diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
> index d15aae6c51c1..36f0ee95b51f 100644
> --- a/drivers/md/bcache/request.c
> +++ b/drivers/md/bcache/request.c
> @@ -13,6 +13,7 @@
>  #include "request.h"
>  #include "writeback.h"
>  +#include <linux/delay.h>
>  #include <linux/module.h>
>  #include <linux/hash.h>
>  #include <linux/random.h>
> @@ -1172,11 +1173,10 @@ void cached_dev_submit_bio(struct bio *bio)
>      unsigned long start_time;
>      int rw = bio_data_dir(bio);
>  -    if (unlikely((d->c && test_bit(CACHE_SET_IO_DISABLE, 
> &d->c->flags)) ||
> +    while (unlikely((d->c && test_bit(CACHE_SET_IO_DISABLE, 
> &d->c->flags)) ||
>               dc->io_disable)) {
> -        bio->bi_status = BLK_STS_IOERR;
> -        bio_endio(bio);
> -        return;
> +        /* wait for detach finish and d->c == NULL. */
> +        msleep(2);
>      }

This is unacceptible, neither the infinite loop nor the msleep. You 
cannot solve the target issue by an infinite retry, such method will 
introduce more issue from other place.


>       if (likely(d->c)) {
> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
> index 140f35dc0c45..8d9a5e937bc8 100644
> --- a/drivers/md/bcache/super.c
> +++ b/drivers/md/bcache/super.c
> @@ -661,7 +661,8 @@ int bch_prio_write(struct cache *ca, bool wait)
>          p->csum        = bch_crc64(&p->magic, 
> meta_bucket_bytes(&ca->sb) - 8);
>           bucket = bch_bucket_alloc(ca, RESERVE_PRIO, wait);
> -        BUG_ON(bucket == -1);
> +        if (bucket == -1)
> +            return -1;

This change is wrong. bucket == -1 indicates the bucket allocator 
doesn't work properly, if it happens something really critical 
happening. This is why BUG_ON is used here.

With the above change, you will encounter other strange issue sooner or 
later and hard to tell the root cause.


> mutex_unlock(&ca->set->bucket_lock);
>          prio_io(ca, bucket, REQ_OP_WRITE, 0);


Currently I don't have clear idea on how to avoid the IO error return 
value during cache set detaching for a failed cache device. But it 
cannot be such simple change by the this patch.


Coly Li

Re: [PATCH] Bcache: don't return BLK_STS_IOERR during cache detach

[Zhang Zhen]

On 3/10/22 5:10 PM, Coly Li wrote:
> On 3/10/22 10:50 AM, Zhang Zhen wrote:
>> Before this patch, if cache device missing, cached_dev_submit_bio 
>> return io err
>> to fs during cache detach, randomly lead to xfs do force shutdown.
>>
>> This patch delay the cache io submit in cached_dev_submit_bio
>> and wait for cache set detach finish.
>> So if the cache device become missing, bcache detach cache set 
>> automatically,
>> and the io will sumbit normally.
>>
>> 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)
>>
>> Signed-off-by: Zhen Zhang <zhangzhen.email@gmail.com>
>> ---
>>  drivers/md/bcache/bcache.h  | 5 -----
>>  drivers/md/bcache/request.c | 8 ++++----
>>  drivers/md/bcache/super.c   | 3 ++-
>>  3 files changed, 6 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
>> index 9ed9c955add7..e5227dd08e3a 100644
>> --- a/drivers/md/bcache/bcache.h
>> +++ b/drivers/md/bcache/bcache.h
>> @@ -928,11 +928,6 @@ static inline void closure_bio_submit(struct 
>> cache_set *c,
>>                        struct closure *cl)
>>  {
>>      closure_get(cl);
>> -    if (unlikely(test_bit(CACHE_SET_IO_DISABLE, &c->flags))) {
>> -        bio->bi_status = BLK_STS_IOERR;
>> -        bio_endio(bio);
>> -        return;
>> -    }
>>      submit_bio_noacct(bio);
>>  }
> 
> 
> Comparing to make bcache device living as it looks like, avoiding data 
> corruption or stale is much more critical. Therefore once there is 
> critical device failure detected, the following I/O requests must be 
> stopped (especially write request) to avoid further data corruption. 
> Without the above checking for CACHE_SET_IO_DISABLE, the cache has to be 
> attached until there is no I/O. For a busy system it should be quite 
> long time. Then users may encounter silent data corruption or 
> inconsistency after a long time since hardware failed.
> 
> 
> Again, with the above change, you may introduce other issue which more 
> hard to detect.
> 
> 
>>  diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
>> index d15aae6c51c1..36f0ee95b51f 100644
>> --- a/drivers/md/bcache/request.c
>> +++ b/drivers/md/bcache/request.c
>> @@ -13,6 +13,7 @@
>>  #include "request.h"
>>  #include "writeback.h"
>>  +#include <linux/delay.h>
>>  #include <linux/module.h>
>>  #include <linux/hash.h>
>>  #include <linux/random.h>
>> @@ -1172,11 +1173,10 @@ void cached_dev_submit_bio(struct bio *bio)
>>      unsigned long start_time;
>>      int rw = bio_data_dir(bio);
>>  -    if (unlikely((d->c && test_bit(CACHE_SET_IO_DISABLE, 
>> &d->c->flags)) ||
>> +    while (unlikely((d->c && test_bit(CACHE_SET_IO_DISABLE, 
>> &d->c->flags)) ||
>>               dc->io_disable)) {
>> -        bio->bi_status = BLK_STS_IOERR;
>> -        bio_endio(bio);
>> -        return;
>> +        /* wait for detach finish and d->c == NULL. */
>> +        msleep(2);
>>      }
> 
> This is unacceptible, neither the infinite loop nor the msleep. You 
> cannot solve the target issue by an infinite retry, such method will 
> introduce more issue from other place.
> 
> 
>>       if (likely(d->c)) {
>> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
>> index 140f35dc0c45..8d9a5e937bc8 100644
>> --- a/drivers/md/bcache/super.c
>> +++ b/drivers/md/bcache/super.c
>> @@ -661,7 +661,8 @@ int bch_prio_write(struct cache *ca, bool wait)
>>          p->csum        = bch_crc64(&p->magic, 
>> meta_bucket_bytes(&ca->sb) - 8);
>>           bucket = bch_bucket_alloc(ca, RESERVE_PRIO, wait);
>> -        BUG_ON(bucket == -1);
>> +        if (bucket == -1)
>> +            return -1;
> 
> This change is wrong. bucket == -1 indicates the bucket allocator 
> doesn't work properly, if it happens something really critical 
> happening. This is why BUG_ON is used here.
> 
> With the above change, you will encounter other strange issue sooner or 
> later and hard to tell the root cause.
> 
> 
>> mutex_unlock(&ca->set->bucket_lock);
>>          prio_io(ca, bucket, REQ_OP_WRITE, 0);
> 
> 
> Currently I don't have clear idea on how to avoid the IO error return 
> value during cache set detaching for a failed cache device. But it 
> cannot be such simple change by the this patch.
Hi Coly,

Thanks for your review，
It seems that this is a difficult problem.

Maybe we can try another method.
If critical device failure detected, we just set IO_DISABLE flag and 
detach cache device. But don't auto recover.

This will at least not confuse users，some disk is normal and some disk 
is error.
Let user recover it manually.
> 
> 
> Coly Li
> 

Re: [PATCH] Bcache: don't return BLK_STS_IOERR during cache detach

[Coly Li]

On 3/14/22 8:04 PM, Zhang Zhen wrote:
>
>
> On 3/10/22 5:10 PM, Coly Li wrote:
>> On 3/10/22 10:50 AM, Zhang Zhen wrote:
>>> Before this patch, if cache device missing, cached_dev_submit_bio 
>>> return io err
>>> to fs during cache detach, randomly lead to xfs do force shutdown.
>>>
>>> This patch delay the cache io submit in cached_dev_submit_bio
>>> and wait for cache set detach finish.
>>> So if the cache device become missing, bcache detach cache set 
>>> automatically,
>>> and the io will sumbit normally.
>>>
>>> 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)
>>>
>>> Signed-off-by: Zhen Zhang <zhangzhen.email@gmail.com>
>>> ---
>>>  drivers/md/bcache/bcache.h  | 5 -----
>>>  drivers/md/bcache/request.c | 8 ++++----
>>>  drivers/md/bcache/super.c   | 3 ++-
>>>  3 files changed, 6 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
>>> index 9ed9c955add7..e5227dd08e3a 100644
>>> --- a/drivers/md/bcache/bcache.h
>>> +++ b/drivers/md/bcache/bcache.h
>>> @@ -928,11 +928,6 @@ static inline void closure_bio_submit(struct 
>>> cache_set *c,
>>>                        struct closure *cl)
>>>  {
>>>      closure_get(cl);
>>> -    if (unlikely(test_bit(CACHE_SET_IO_DISABLE, &c->flags))) {
>>> -        bio->bi_status = BLK_STS_IOERR;
>>> -        bio_endio(bio);
>>> -        return;
>>> -    }
>>>      submit_bio_noacct(bio);
>>>  }
>>
>>
>> Comparing to make bcache device living as it looks like, avoiding 
>> data corruption or stale is much more critical. Therefore once there 
>> is critical device failure detected, the following I/O requests must 
>> be stopped (especially write request) to avoid further data 
>> corruption. Without the above checking for CACHE_SET_IO_DISABLE, the 
>> cache has to be attached until there is no I/O. For a busy system it 
>> should be quite long time. Then users may encounter silent data 
>> corruption or inconsistency after a long time since hardware failed.
>>
>>
>> Again, with the above change, you may introduce other issue which 
>> more hard to detect.
>>
>>
>>>  diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
>>> index d15aae6c51c1..36f0ee95b51f 100644
>>> --- a/drivers/md/bcache/request.c
>>> +++ b/drivers/md/bcache/request.c
>>> @@ -13,6 +13,7 @@
>>>  #include "request.h"
>>>  #include "writeback.h"
>>>  +#include <linux/delay.h>
>>>  #include <linux/module.h>
>>>  #include <linux/hash.h>
>>>  #include <linux/random.h>
>>> @@ -1172,11 +1173,10 @@ void cached_dev_submit_bio(struct bio *bio)
>>>      unsigned long start_time;
>>>      int rw = bio_data_dir(bio);
>>>  -    if (unlikely((d->c && test_bit(CACHE_SET_IO_DISABLE, 
>>> &d->c->flags)) ||
>>> +    while (unlikely((d->c && test_bit(CACHE_SET_IO_DISABLE, 
>>> &d->c->flags)) ||
>>>               dc->io_disable)) {
>>> -        bio->bi_status = BLK_STS_IOERR;
>>> -        bio_endio(bio);
>>> -        return;
>>> +        /* wait for detach finish and d->c == NULL. */
>>> +        msleep(2);
>>>      }
>>
>> This is unacceptible, neither the infinite loop nor the msleep. You 
>> cannot solve the target issue by an infinite retry, such method will 
>> introduce more issue from other place.
>>
>>
>>>       if (likely(d->c)) {
>>> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
>>> index 140f35dc0c45..8d9a5e937bc8 100644
>>> --- a/drivers/md/bcache/super.c
>>> +++ b/drivers/md/bcache/super.c
>>> @@ -661,7 +661,8 @@ int bch_prio_write(struct cache *ca, bool wait)
>>>          p->csum        = bch_crc64(&p->magic, 
>>> meta_bucket_bytes(&ca->sb) - 8);
>>>           bucket = bch_bucket_alloc(ca, RESERVE_PRIO, wait);
>>> -        BUG_ON(bucket == -1);
>>> +        if (bucket == -1)
>>> +            return -1;
>>
>> This change is wrong. bucket == -1 indicates the bucket allocator 
>> doesn't work properly, if it happens something really critical 
>> happening. This is why BUG_ON is used here.
>>
>> With the above change, you will encounter other strange issue sooner 
>> or later and hard to tell the root cause.
>>
>>
>>> mutex_unlock(&ca->set->bucket_lock);
>>>          prio_io(ca, bucket, REQ_OP_WRITE, 0);
>>
>>
>> Currently I don't have clear idea on how to avoid the IO error return 
>> value during cache set detaching for a failed cache device. But it 
>> cannot be such simple change by the this patch.
> Hi Coly,
>
> Thanks for your review，
> It seems that this is a difficult problem.
>
> Maybe we can try another method.
> If critical device failure detected, we just set IO_DISABLE flag and 
> detach cache device. But don't auto recover.


What do you mean on "auto recover", could you describe it with more 
details ?


>
> This will at least not confuse users，some disk is normal and some disk 
> is error.
> Let user recover it manually.

When you see panic, it is from XFS meta data I/O error, which is 
critical to XFS and trigger its panic. When the I/O error happens for 
normal file system data blocks, the user space receives I/O error return 
values that's why you don't see the panic.

In your case, the cache device is always clean, so cache device failure 
will detach the cache from backing device. It will be better if we can 
re-read data from backing device if no dirty data on cache, but we need 
to handle the potential race window between cache-seen-clean and 
read-from-backing-device, because the cache mode can change on-fly and 
writing may come at any time. This is not simple and should be careful, 
but it can be improved.


Coly Li

Re: [PATCH] Bcache: don't return BLK_STS_IOERR during cache detach

[Zhang Zhen]

On 3/14/22 8:57 PM, Coly Li wrote:
> On 3/14/22 8:04 PM, Zhang Zhen wrote:
>>
>>
>> On 3/10/22 5:10 PM, Coly Li wrote:
>>> On 3/10/22 10:50 AM, Zhang Zhen wrote:
>>>> Before this patch, if cache device missing, cached_dev_submit_bio 
>>>> return io err
>>>> to fs during cache detach, randomly lead to xfs do force shutdown.
>>>>
>>>> This patch delay the cache io submit in cached_dev_submit_bio
>>>> and wait for cache set detach finish.
>>>> So if the cache device become missing, bcache detach cache set 
>>>> automatically,
>>>> and the io will sumbit normally.
>>>>
>>>> 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)
>>>>
>>>> Signed-off-by: Zhen Zhang <zhangzhen.email@gmail.com>
>>>> ---
>>>>  drivers/md/bcache/bcache.h  | 5 -----
>>>>  drivers/md/bcache/request.c | 8 ++++----
>>>>  drivers/md/bcache/super.c   | 3 ++-
>>>>  3 files changed, 6 insertions(+), 10 deletions(-)
>>>>
>>>> diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
>>>> index 9ed9c955add7..e5227dd08e3a 100644
>>>> --- a/drivers/md/bcache/bcache.h
>>>> +++ b/drivers/md/bcache/bcache.h
>>>> @@ -928,11 +928,6 @@ static inline void closure_bio_submit(struct 
>>>> cache_set *c,
>>>>                        struct closure *cl)
>>>>  {
>>>>      closure_get(cl);
>>>> -    if (unlikely(test_bit(CACHE_SET_IO_DISABLE, &c->flags))) {
>>>> -        bio->bi_status = BLK_STS_IOERR;
>>>> -        bio_endio(bio);
>>>> -        return;
>>>> -    }
>>>>      submit_bio_noacct(bio);
>>>>  }
>>>
>>>
>>> Comparing to make bcache device living as it looks like, avoiding 
>>> data corruption or stale is much more critical. Therefore once there 
>>> is critical device failure detected, the following I/O requests must 
>>> be stopped (especially write request) to avoid further data 
>>> corruption. Without the above checking for CACHE_SET_IO_DISABLE, the 
>>> cache has to be attached until there is no I/O. For a busy system it 
>>> should be quite long time. Then users may encounter silent data 
>>> corruption or inconsistency after a long time since hardware failed.
>>>
>>>
>>> Again, with the above change, you may introduce other issue which 
>>> more hard to detect.
>>>
>>>
>>>>  diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
>>>> index d15aae6c51c1..36f0ee95b51f 100644
>>>> --- a/drivers/md/bcache/request.c
>>>> +++ b/drivers/md/bcache/request.c
>>>> @@ -13,6 +13,7 @@
>>>>  #include "request.h"
>>>>  #include "writeback.h"
>>>>  +#include <linux/delay.h>
>>>>  #include <linux/module.h>
>>>>  #include <linux/hash.h>
>>>>  #include <linux/random.h>
>>>> @@ -1172,11 +1173,10 @@ void cached_dev_submit_bio(struct bio *bio)
>>>>      unsigned long start_time;
>>>>      int rw = bio_data_dir(bio);
>>>>  -    if (unlikely((d->c && test_bit(CACHE_SET_IO_DISABLE, 
>>>> &d->c->flags)) ||
>>>> +    while (unlikely((d->c && test_bit(CACHE_SET_IO_DISABLE, 
>>>> &d->c->flags)) ||
>>>>               dc->io_disable)) {
>>>> -        bio->bi_status = BLK_STS_IOERR;
>>>> -        bio_endio(bio);
>>>> -        return;
>>>> +        /* wait for detach finish and d->c == NULL. */
>>>> +        msleep(2);
>>>>      }
>>>
>>> This is unacceptible, neither the infinite loop nor the msleep. You 
>>> cannot solve the target issue by an infinite retry, such method will 
>>> introduce more issue from other place.
>>>
>>>
>>>>       if (likely(d->c)) {
>>>> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
>>>> index 140f35dc0c45..8d9a5e937bc8 100644
>>>> --- a/drivers/md/bcache/super.c
>>>> +++ b/drivers/md/bcache/super.c
>>>> @@ -661,7 +661,8 @@ int bch_prio_write(struct cache *ca, bool wait)
>>>>          p->csum        = bch_crc64(&p->magic, 
>>>> meta_bucket_bytes(&ca->sb) - 8);
>>>>           bucket = bch_bucket_alloc(ca, RESERVE_PRIO, wait);
>>>> -        BUG_ON(bucket == -1);
>>>> +        if (bucket == -1)
>>>> +            return -1;
>>>
>>> This change is wrong. bucket == -1 indicates the bucket allocator 
>>> doesn't work properly, if it happens something really critical 
>>> happening. This is why BUG_ON is used here.
>>>
>>> With the above change, you will encounter other strange issue sooner 
>>> or later and hard to tell the root cause.
>>>
>>>
>>>> mutex_unlock(&ca->set->bucket_lock);
>>>>          prio_io(ca, bucket, REQ_OP_WRITE, 0);
>>>
>>>
>>> Currently I don't have clear idea on how to avoid the IO error return 
>>> value during cache set detaching for a failed cache device. But it 
>>> cannot be such simple change by the this patch.
>> Hi Coly,
>>
>> Thanks for your review，
>> It seems that this is a difficult problem.
>>
>> Maybe we can try another method.
>> If critical device failure detected, we just set IO_DISABLE flag and 
>> detach cache device. But don't auto recover.
> 
> 
> What do you mean on "auto recover", could you describe it with more 
> details ?
> 
"auto recover" means bcache return io error only during the detach time.
It will submit io to bdev after the detach finished.
> 
>>
>> This will at least not confuse users，some disk is normal and some 
>> disk is error.
>> Let user recover it manually.
> 
> When you see panic, it is from XFS meta data I/O error, which is 
> critical to XFS and trigger its panic. When the I/O error happens for 
> normal file system data blocks, the user space receives I/O error return 
> values that's why you don't see the panic.
> 
Thanks for your reminding.
> In your case, the cache device is always clean, so cache device failure 
> will detach the cache from backing device. It will be better if we can 
> re-read data from backing device if no dirty data on cache, but we need 
> to handle the potential race window between cache-seen-clean and 
> read-from-backing-device, because the cache mode can change on-fly and 
> writing may come at any time. This is not simple and should be careful, 
> but it can be improved.
> 
> 
> Coly Li
> 
> 
> 

Re: bcache detach lead to xfs force shutdown

[Coly Li]

On 3/7/22 3:56 PM, zhangzhen.email@gmail.com wrote:

>> >>
>> >> 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.
>>
>>
>> Hi Zhen and Nix,
>>
>> OK, I come to realize the motivation. Yes you are right, this is an 
>> awkward issue and good to be fixed.
>>
> Hi Coly,
>
> So you will pick this patch into your tree ？


I need to look the patch firstly, could you please post a proposal patch 
for review ?


Coly Li

[PATCH] Bcache: don't return BLK_STS_IOERR during cache detach

[Zhen Zhang]

Before this patch, if cache device missing, cached_dev_submit_bio return io err
to fs during cache detach, randomly lead to xfs do force shutdown.

This patch delay the cache io submit in cached_dev_submit_bio
and wait for cache set detach finish.
So if the cache device become missing, bcache detach cache set automatically,
and the io will sumbit normally.

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)

Signed-off-by: Zhen Zhang <zhangzhen.email@gmail.com>
---
 drivers/md/bcache/bcache.h  | 5 -----
 drivers/md/bcache/request.c | 8 ++++----
 drivers/md/bcache/super.c   | 3 ++-
 3 files changed, 6 insertions(+), 10 deletions(-)

diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
index 9ed9c955add7..e5227dd08e3a 100644
--- a/drivers/md/bcache/bcache.h
+++ b/drivers/md/bcache/bcache.h
@@ -928,11 +928,6 @@ static inline void closure_bio_submit(struct cache_set *c,
 				      struct closure *cl)
 {
 	closure_get(cl);
-	if (unlikely(test_bit(CACHE_SET_IO_DISABLE, &c->flags))) {
-		bio->bi_status = BLK_STS_IOERR;
-		bio_endio(bio);
-		return;
-	}
 	submit_bio_noacct(bio);
 }
 
diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
index d15aae6c51c1..36f0ee95b51f 100644
--- a/drivers/md/bcache/request.c
+++ b/drivers/md/bcache/request.c
@@ -13,6 +13,7 @@
 #include "request.h"
 #include "writeback.h"
 
+#include <linux/delay.h>
 #include <linux/module.h>
 #include <linux/hash.h>
 #include <linux/random.h>
@@ -1172,11 +1173,10 @@ void cached_dev_submit_bio(struct bio *bio)
 	unsigned long start_time;
 	int rw = bio_data_dir(bio);
 
-	if (unlikely((d->c && test_bit(CACHE_SET_IO_DISABLE, &d->c->flags)) ||
+	while (unlikely((d->c && test_bit(CACHE_SET_IO_DISABLE, &d->c->flags)) ||
 		     dc->io_disable)) {
-		bio->bi_status = BLK_STS_IOERR;
-		bio_endio(bio);
-		return;
+		/* wait for detach finish and d->c == NULL. */
+		msleep(2);
 	}
 
 	if (likely(d->c)) {
diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 140f35dc0c45..8d9a5e937bc8 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -661,7 +661,8 @@ int bch_prio_write(struct cache *ca, bool wait)
 		p->csum		= bch_crc64(&p->magic, meta_bucket_bytes(&ca->sb) - 8);
 
 		bucket = bch_bucket_alloc(ca, RESERVE_PRIO, wait);
-		BUG_ON(bucket == -1);
+		if (bucket == -1)
+			return -1;
 
 		mutex_unlock(&ca->set->bucket_lock);
 		prio_io(ca, bucket, REQ_OP_WRITE, 0);
-- 
2.25.1