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@xxxxxxxxx>
---
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
