It seems alloc_bucket_pages() is the only user of bucket_pages().
Considering alloc_bucket_pages() is removed from bcache code, it is safe
to remove the useless macro bucket_pages() now.
Signed-off-by: NColy Li <colyli@suse.de>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Because struct cache_set and struct cache both have struct cache_sb,
therefore macro block_bytes() can be used on both of them. When removing
the embedded struct cache_sb from struct cache_set, this macro won't be
used on struct cache_set anymore.

This patch unifies all block_bytes() usage only on struct cache, this is
one of the preparation to remove the embedded struct cache_sb from
struct cache_set.
Signed-off-by: NColy Li <colyli@suse.de>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

This patch adds a separated set_uuid[16] in struct cache_set, to store
the uuid of the cache set. This is the preparation to remove the
embedded struct cache_sb from struct cache_set.
Signed-off-by: NColy Li <colyli@suse.de>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Since now each cache_set explicitly has single cache, for_each_cache()
is unnecessary. This patch removes this macro, and update all locations
where it is used, and makes sure all code logic still being consistent.
Signed-off-by: NColy Li <colyli@suse.de>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Currently although the bcache code has a framework for multiple caches
in a cache set, but indeed the multiple caches never completed and users
use md raid1 for multiple copies of the cached data.

This patch does the following change in struct cache_set, to explicitly
make a cache_set only have single cache,
- Change pointer array "*cache[MAX_CACHES_PER_SET]" to a single pointer
  "*cache".
- Remove pointer array "*cache_by_alloc[MAX_CACHES_PER_SET]".
- Remove "caches_loaded".

Now the code looks as exactly what it does in practic: only one cache is
used in the cache set.
Signed-off-by: NColy Li <colyli@suse.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

The parameter 'int n' from bch_bucket_alloc_set() is not cleared
defined. From the code comments n is the number of buckets to alloc, but
from the code itself 'n' is the maximum cache to iterate. Indeed all the
locations where bch_bucket_alloc_set() is called, 'n' is alwasy 1.

This patch removes the confused and unnecessary 'int n' from parameter
list of  bch_bucket_alloc_set(), and explicitly allocates only 1 bucket
for its caller.
Signed-off-by: NColy Li <colyli@suse.de>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Similar to c->uuids, struct cache's prio_buckets and disk_buckets also
have the potential memory allocation failure during cache registration
if the bucket size > 8MB.

ca->prio_buckets can be stored on cache device in multiple buckets, its
in-memory space is allocated by kzalloc() interface but normally
allocated by alloc_pages() because the size > KMALLOC_MAX_CACHE_SIZE.

So allocation of ca->prio_buckets has the MAX_ORDER restriction too. If
the bucket size > 8MB, by default the page allocator will fail because
the page order > 11 (default MAX_ORDER value). ca->prio_buckets should
also use meta_bucket_bytes(), meta_bucket_pages() to decide its memory
size and use alloc_meta_bucket_pages() to allocate pages, to avoid the
allocation failure during cache set registration when bucket size > 8MB.

ca->disk_buckets is a single bucket size memory buffer, it is used to
iterate each bucket of ca->prio_buckets, and compose the bio based on
memory of ca->disk_buckets, then write ca->disk_buckets memory to cache
disk one-by-one for each bucket of ca->prio_buckets. ca->disk_buckets
should have in-memory size exact to the meta_bucket_pages(), this is the
size that ca->prio_buckets will be stored into each on-disk bucket.

This patch fixes the above issues and handle cache's prio_buckets and
disk_buckets properly for bucket size larger than 8MB.
Signed-off-by: NColy Li <colyli@suse.de>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Currently the in-memory meta data like c->uuids or c->disk_buckets
are allocated by alloc_bucket_pages(). The macro alloc_bucket_pages()
calls __get_free_pages() to allocated continuous pages with order
indicated by ilog2(bucket_pages(c)),
 #define alloc_bucket_pages(gfp, c)                      \
     ((void *) __get_free_pages(__GFP_ZERO|gfp, ilog2(bucket_pages(c))))

The maximum order is defined as MAX_ORDER, the default value is 11 (and
can be overwritten by CONFIG_FORCE_MAX_ZONEORDER). In bcache code the
maximum bucket size width is 16bits, this is restricted both by KEY_SIZE
size and bucket_size size from struct cache_sb_disk. The maximum 16bits
width and power-of-2 value is (1<<15) in unit of sector (512byte). It
means the maximum value of bucket size in bytes is (1<<24) bytes a.k.a
4096 pages.

When the bucket size is set to maximum permitted value, ilog2(4096) is
12, which exceeds the default maximum order __get_free_pages() can
accepted, the failed pages allocation will fail cache set registration
procedure and print a kernel oops message for the exceeded pages order.

This patch introduces meta_bucket_pages(), meta_bucket_bytes(), and
alloc_bucket_pages() helper routines. meta_bucket_pages() indicates the
maximum pages can be allocated to meta data bucket, meta_bucket_bytes()
indicates the according maximum bytes, and alloc_bucket_pages() does
the pages allocation for meta bucket. Because meta_bucket_pages()
chooses the smaller value among the bucket size and MAX_ORDER_NR_PAGES,
it still works when MAX_ORDER overwritten by CONFIG_FORCE_MAX_ZONEORDER.

Following patches will use these helper routines to decide maximum pages
can be allocated for different meta data buckets. If the bucket size is
larger than meta_bucket_bytes(), the bcache registration can continue to
success, just the space more than meta_bucket_bytes() inside the bucket
is wasted. Comparing bcache failed for large bucket size, wasting some
space for meta data buckets is acceptable at this moment.
Signed-off-by: NColy Li <colyli@suse.de>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

offset_to_stripe() returns the stripe number (in type unsigned int) from
an offset (in type uint64_t) by the following calculation,
	do_div(offset, d->stripe_size);
For large capacity backing device (e.g. 18TB) with small stripe size
(e.g. 4KB), the result is 4831838208 and exceeds UINT_MAX. The actual
returned value which caller receives is 536870912, due to the overflow.

Indeed in bcache_device_init(), bcache_device->nr_stripes is limited in
range [1, INT_MAX]. Therefore all valid stripe numbers in bcache are
in range [0, bcache_dev->nr_stripes - 1].

This patch adds a upper limition check in offset_to_stripe(): the max
valid stripe number should be less than bcache_device->nr_stripes. If
the calculated stripe number from do_div() is equal to or larger than
bcache_device->nr_stripe, -EINVAL will be returned. (Normally nr_stripes
is less than INT_MAX, exceeding upper limitation doesn't mean overflow,
therefore -EOVERFLOW is not used as error code.)

This patch also changes nr_stripes' type of struct bcache_device from
'unsigned int' to 'int', and return value type of offset_to_stripe()
from 'unsigned int' to 'int', to match their exact data ranges.

All locations where bcache_device->nr_stripes and offset_to_stripe() are
referenced also get updated for the above type change.
Reported-and-tested-by: NKen Raeburn <raeburn@redhat.com>
Signed-off-by: NColy Li <colyli@suse.de>
Cc: stable@vger.kernel.org
Link: https://bugzilla.redhat.com/show_bug.cgi?id=1783075Signed-off-by: NJens Axboe <axboe@kernel.dk>

generic_make_request has always been very confusingly misnamed, so rename
it to submit_bio_noacct to make it clear that it is submit_bio minus
accounting and a few checks.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Remove the trailing newline from the define of pr_fmt and add newlines
to the uses.

Miscellanea:

o Convert bch_bkey_dump from multiple uses of pr_err to pr_cont
  as the earlier conversion was inappropriate done causing multiple
  lines to be emitted where only a single output line was desired
o Use vsprintf extension %pV in bch_cache_set_error to avoid multiple
  line output where only a single line output was desired
o Coalesce formats

Fixes: 6ae63e35 ("bcache: replace printk() by pr_*() routines")
Signed-off-by: NJoe Perches <joe@perches.com>
Signed-off-by: NColy Li <colyli@suse.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

In year 2007 high performance SSD was still expensive, in order to
save more space for real workload or meta data, the readahead I/Os
for non-meta data was bypassed and not cached on SSD.

In now days, SSD price drops a lot and people can find larger size
SSD with more comfortable price. It is unncessary to alway bypass
normal readahead I/Os to save SSD space for now.

This patch adds options for readahead data cache policies via sysfs
file /sys/block/bcache<N>/readahead_cache_policy, the options are,
- "all": cache all readahead data I/Os.
- "meta-only": only cache meta data, and bypass other regular I/Os.

If users want to make bcache continue to only cache readahead request
for metadata and bypass regular data readahead, please set "meta-only"
to this sysfs file. By default, bcache will back to cache all read-
ahead requests now.

Cc: stable@vger.kernel.org
Signed-off-by: NColy Li <colyli@suse.de>
Acked-by: NEric Wheeler <bcache@linux.ewheeler.net>
Cc: Michael Lyle <mlyle@lyle.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

This allows to properly build the superblock bio including the offset in
the page using the normal bio helpers.  This fixes writing the superblock
for page sizes larger than 4k where the sb write bio would need an offset
in the bio_vec.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NColy Li <colyli@suse.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

For writeback mode, if there is no regular I/O request for a while,
the writeback rate will be set to the maximum value (1TB/s for now).
This is good for most of the storage workload, but there are still
people don't what the maximum writeback rate in I/O idle time.

This patch adds a sysfs interface file idle_max_writeback_rate to
permit people to disable maximum writeback rate. Then the minimum
writeback rate can be advised by writeback_rate_minimum in the
bcache device's sysfs interface.
Reported-by: NChristian Balzer <chibi@gol.com>
Signed-off-by: NColy Li <colyli@suse.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

bcache_allocator can call the following:

 bch_allocator_thread()
  -> bch_prio_write()
     -> bch_bucket_alloc()
        -> wait on &ca->set->bucket_wait

But the wake up event on bucket_wait is supposed to come from
bch_allocator_thread() itself => deadlock:

[ 1158.490744] INFO: task bcache_allocato:15861 blocked for more than 10 seconds.
[ 1158.495929]       Not tainted 5.3.0-050300rc3-generic #201908042232
[ 1158.500653] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 1158.504413] bcache_allocato D    0 15861      2 0x80004000
[ 1158.504419] Call Trace:
[ 1158.504429]  __schedule+0x2a8/0x670
[ 1158.504432]  schedule+0x2d/0x90
[ 1158.504448]  bch_bucket_alloc+0xe5/0x370 [bcache]
[ 1158.504453]  ? wait_woken+0x80/0x80
[ 1158.504466]  bch_prio_write+0x1dc/0x390 [bcache]
[ 1158.504476]  bch_allocator_thread+0x233/0x490 [bcache]
[ 1158.504491]  kthread+0x121/0x140
[ 1158.504503]  ? invalidate_buckets+0x890/0x890 [bcache]
[ 1158.504506]  ? kthread_park+0xb0/0xb0
[ 1158.504510]  ret_from_fork+0x35/0x40

Fix by making the call to bch_prio_write() non-blocking, so that
bch_allocator_thread() never waits on itself.

Moreover, make sure to wake up the garbage collector thread when
bch_prio_write() is failing to allocate buckets.

BugLink: https://bugs.launchpad.net/bugs/1784665
BugLink: https://bugs.launchpad.net/bugs/1796292Signed-off-by: NAndrea Righi <andrea.righi@canonical.com>
Signed-off-by: NColy Li <colyli@suse.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

This patch fix a lost wake-up problem caused by the race between
mca_cannibalize_lock and bch_cannibalize_unlock.

Consider two processes, A and B. Process A is executing
mca_cannibalize_lock, while process B takes c->btree_cache_alloc_lock
and is executing bch_cannibalize_unlock. The problem happens that after
process A executes cmpxchg and will execute prepare_to_wait. In this
timeslice process B executes wake_up, but after that process A executes
prepare_to_wait and set the state to TASK_INTERRUPTIBLE. Then process A
goes to sleep but no one will wake up it. This problem may cause bcache
device to dead.
Signed-off-by: NGuoju Fang <fangguoju@gmail.com>
Signed-off-by: NColy Li <colyli@suse.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Now we have counters for how many times jouranl is reclaimed, how many
times cached dirty btree nodes are flushed, but we don't know how many
jouranl buckets are really reclaimed.

This patch adds reclaimed_journal_buckets into struct cache_set, this
is an increasing only counter, to tell how many journal buckets are
reclaimed since cache set runs. From all these three counters (reclaim,
reclaimed_journal_buckets, flush_write), we can have idea how well
current journal space reclaim code works.
Signed-off-by: NColy Li <colyli@suse.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

In struct cache_set, retry_flush_write is added for commit c4dc2497
("bcache: fix high CPU occupancy during journal") which is reverted in
previous patch.

Now it is useless anymore, and this patch removes it from bcache code.
Signed-off-by: NColy Li <colyli@suse.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

This reverts commit c4dc2497.

This patch enlarges a race between normal btree flush code path and
flush_btree_write(), which causes deadlock when journal space is
exhausted. Reverts this patch makes the race window from 128 btree
nodes to only 1 btree nodes.

Fixes: c4dc2497 ("bcache: fix high CPU occupancy during journal")
Signed-off-by: NColy Li <colyli@suse.de>
Cc: stable@vger.kernel.org
Cc: Tang Junhui <tang.junhui.linux@gmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

This patch adds return value check to bch_cached_dev_run(), now if there
is error happens inside bch_cached_dev_run(), it can be catched.
Signed-off-by: NColy Li <colyli@suse.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

The option gc_after_writeback is disabled by default, because garbage
collection will discard SSD data which drops cached data.

Echo 1 into /sys/fs/bcache/<UUID>/internal/gc_after_writeback will
enable this option, which wakes up gc thread when writeback accomplished
and all cached data is clean.

This option is helpful for people who cares writing performance more. In
heavy writing workload, all cached data can be clean only happens when
writeback thread cleans all cached data in I/O idle time. In such
situation a following gc running may help to shrink bcache B+ tree and
discard more clean data, which may be helpful for future writing
requests.

If you are not sure whether this is helpful for your own workload,
please leave it as disabled by default.
Signed-off-by: NColy Li <colyli@suse.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

We have the following define for btree iterator:
	struct btree_iter {
		size_t size, used;
	#ifdef CONFIG_BCACHE_DEBUG
		struct btree_keys *b;
	#endif
		struct btree_iter_set {
			struct bkey *k, *end;
		} data[MAX_BSETS];
	};

We can see that the length of data[] field is static MAX_BSETS, which is
defined as 4 currently.

But a btree node on disk could have too many bsets for an iterator to fit
on the stack - maybe far more that MAX_BSETS. Have to dynamically allocate
space to host more btree_iter_sets.

bch_cache_set_alloc() will make sure the pool cache_set->fill_iter can
allocate an iterator equipped with enough room that can host
	(sb.bucket_size / sb.block_size)
btree_iter_sets, which is more than static MAX_BSETS.

bch_btree_node_read_done() will use that pool to allocate one iterator, to
host many bsets in one btree node.

Add more comment around cache_set->fill_iter to make code less confusing.
Signed-off-by: NShenghui Wang <shhuiw@foxmail.com>
Signed-off-by: NColy Li <colyli@suse.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Parameter "struct kobject *kobj" in bch_debug_init() is useless,
remove it in this patch.
Signed-off-by: NDongbo Cao <cdbdyx@163.com>
Signed-off-by: NColy Li <colyli@suse.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

After write SSD completed, bcache schedules journal_write work to
system_wq, which is a public workqueue in system, without WQ_MEM_RECLAIM
flag. system_wq is also a bound wq, and there may be no idle kworker on
current processor. Creating a new kworker may unfortunately need to
reclaim memory first, by shrinking cache and slab used by vfs, which
depends on bcache device. That's a deadlock.

This patch create a new workqueue for journal_write with WQ_MEM_RECLAIM
flag. It's rescuer thread will work to avoid the deadlock.
Signed-off-by: NGuoju Fang <fangguoju@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: NColy Li <colyli@suse.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

This is warned by checkpatch.pl, this patch removes the extra space.
Signed-off-by: NColy Li <colyli@suse.de>
Reviewed-by: NShenghui Wang <shhuiw@foxmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Symbolic permission names are used in bcache, for now octal permission
numbers are encouraged to use for readability. This patch replaces
all symbolic permissions by octal permission numbers.
Signed-off-by: NColy Li <colyli@suse.de>
Reviewed-by: NShenghui Wang <shhuiw@foxmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

This patch fixes the lines over 80 characters into more lines, to minimize
warnings by checkpatch.pl. There are still some lines exceed 80 characters,
but it is better to be a single line and I don't change them.
Signed-off-by: NColy Li <colyli@suse.de>
Reviewed-by: NShenghui Wang <shhuiw@foxmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

There are many function definitions do not have identifier argument names,
scripts/checkpatch.pl complains warnings like this,

 WARNING: function definition argument 'struct bcache_device *' should
  also have an identifier name
  #16735: FILE: writeback.h:120:
  +void bch_sectors_dirty_init(struct bcache_device *);

This patch adds identifier argument names to all bcache function
definitions to fix such warnings.
Signed-off-by: NColy Li <colyli@suse.de>
Reviewed: Shenghui Wang <shhuiw@foxmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Signed-off-by: NColy Li <colyli@suse.de>
Reviewed-by: NShenghui Wang <shhuiw@foxmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

This patch fixes warning reported by checkpatch.pl by replacing 'unsigned'
with 'unsigned int'.
Signed-off-by: NColy Li <colyli@suse.de>
Reviewed-by: NShenghui Wang <shhuiw@foxmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Commit b1092c9a ("bcache: allow quick writeback when backing idle")
allows the writeback rate to be faster if there is no I/O request on a
bcache device. It works well if there is only one bcache device attached
to the cache set. If there are many bcache devices attached to a cache
set, it may introduce performance regression because multiple faster
writeback threads of the idle bcache devices will compete the btree level
locks with the bcache device who have I/O requests coming.

This patch fixes the above issue by only permitting fast writebac when
all bcache devices attached on the cache set are idle. And if one of the
bcache devices has new I/O request coming, minimized all writeback
throughput immediately and let PI controller __update_writeback_rate()
to decide the upcoming writeback rate for each bcache device.

Also when all bcache devices are idle, limited wrieback rate to a small
number is wast of thoughput, especially when backing devices are slower
non-rotation devices (e.g. SATA SSD). This patch sets a max writeback
rate for each backing device if the whole cache set is idle. A faster
writeback rate in idle time means new I/Os may have more available space
for dirty data, and people may observe a better write performance then.

Please note bcache may change its cache mode in run time, and this patch
still works if the cache mode is switched from writeback mode and there
is still dirty data on cache.

Fixes: Commit b1092c9a ("bcache: allow quick writeback when backing idle")
Cc: stable@vger.kernel.org #4.16+
Signed-off-by: NColy Li <colyli@suse.de>
Tested-by: NKai Krakow <kai@kaishome.de>
Tested-by: NStefan Priebe <s.priebe@profihost.ag>
Cc: Michael Lyle <mlyle@lyle.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

This patch updates the code comment in struct cache with correct array
names, to make the code to be more comprehensible.
Signed-off-by: NColy Li <colyli@suse.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Greg KH suggests that normal code should not care about debugfs. Therefore
no matter successful or failed of debugfs_create_dir() execution, it is
unncessary to check its return value.

There are two functions called debugfs_create_dir() and check the return
value, which are bch_debug_init() and closure_debug_init(). This patch
changes these two functions from int to void type, and ignore return values
of debugfs_create_dir().

This patch does not fix exact bug, just makes things work as they should.
Signed-off-by: NColy Li <colyli@suse.de>
Suggested-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: stable@vger.kernel.org
Cc: Kai Krakow <kai@kaishome.de>
Cc: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

In GC thread, we record the latest GC key in gc_done, which is expected
to be used for incremental GC, but in currently code, we didn't realize
it. When GC runs, front side IO would be blocked until the GC over, it
would be a long time if there is a lot of btree nodes.

This patch realizes incremental GC, the main ideal is that, when there
are front side I/Os, after GC some nodes (100), we stop GC, release locker
of the btree node, and go to process the front side I/Os for some times
(100 ms), then go back to GC again.

By this patch, when we doing GC, I/Os are not blocked all the time, and
there is no obvious I/Os zero jump problem any more.

Patch v2: Rename some variables and macros name as Coly suggested.
Signed-off-by: NTang Junhui <tang.junhui@zte.com.cn>
Signed-off-by: NColy Li <colyli@suse.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Currently we calculate the total amount of flash only devices dirty data
by adding the dirty data of each flash only device under registering
locker. It is very inefficient.

In this patch, we add a member flash_dev_dirty_sectors in struct cache_set
to record the total amount of flash only devices dirty data in real time,
so we didn't need to calculate the total amount of dirty data any more.
Signed-off-by: NTang Junhui <tang.junhui@zte.com.cn>
Signed-off-by: NColy Li <colyli@suse.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Convert bcache to embedded bio sets.
Reviewed-by: NColy Li <colyli@suse.de>
Signed-off-by: NKent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

There is couple of string arrays that are used exclusively in sysfs.c.
Move it to there and make them static.

Besides above, it will allow further clean up.

No functional change intended.
Signed-off-by: NAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: NColy Li <colyli@suse.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Currently bcache does not handle backing device failure, if backing
device is offline and disconnected from system, its bcache device can still
be accessible. If the bcache device is in writeback mode, I/O requests even
can success if the requests hit on cache device. That is to say, when and
how bcache handles offline backing device is undefined.

This patch tries to handle backing device offline in a rather simple way,
- Add cached_dev->status_update_thread kernel thread to update backing
  device status in every 1 second.
- Add cached_dev->offline_seconds to record how many seconds the backing
  device is observed to be offline. If the backing device is offline for
  BACKING_DEV_OFFLINE_TIMEOUT (30) seconds, set dc->io_disable to 1 and
  call bcache_device_stop() to stop the bache device which linked to the
  offline backing device.

Now if a backing device is offline for BACKING_DEV_OFFLINE_TIMEOUT seconds,
its bcache device will be removed, then user space application writing on
it will get error immediately, and handler the device failure in time.

This patch is quite simple, does not handle more complicated situations.
Once the bcache device is stopped, users need to recovery the backing
device, register and attach it manually.

Changelog:
v3: call wait_for_kthread_stop() before exits kernel thread.
v2: remove "bcache: " prefix when calling pr_warn().
v1: initial version.
Signed-off-by: NColy Li <colyli@suse.de>
Reviewed-by: NHannes Reinecke <hare@suse.com>
Cc: Michael Lyle <mlyle@lyle.org>
Cc: Junhui Tang <tang.junhui@zte.com.cn>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Current code uses bdevname() or bio_devname() to reference gendisk
disk name when bcache needs to display the disk names in kernel message.
It was safe before bcache device failure handling patch set merged in,
because when devices are failed, there was deadlock to prevent bcache
printing error messages with gendisk disk name. But after the failure
handling patch set merged, the deadlock is fixed, so it is possible
that the gendisk structure bdev->hd_disk is released when bdevname() is
called to reference bdev->bd_disk->disk_name[]. This is why I receive
bug report of NULL pointers deference panic.

This patch stores gendisk disk name in a buffer inside struct cache and
struct cached_dev, then print out the offline device name won't reference
bdev->hd_disk anymore. And this patch also avoids extra function calls
of bdevname() and bio_devnmae().

Changelog:
v3, add Reviewed-by from Hannes.
v2, call bdevname() earlier in register_bdev()
v1, first version with segguestion from Junhui Tang.

Fixes: c7b7bd07 ("bcache: add io_disable to struct cached_dev")
Fixes: 5138ac67 ("bcache: fix misleading error message in bch_count_io_errors()")
Signed-off-by: NColy Li <colyli@suse.de>
Reviewed-by: NHannes Reinecke <hare@suse.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

If a bcache device is configured to writeback mode, current code does not
handle write I/O errors on backing devices properly.

In writeback mode, write request is written to cache device, and
latter being flushed to backing device. If I/O failed when writing from
cache device to the backing device, bcache code just ignores the error and
upper layer code is NOT noticed that the backing device is broken.

This patch tries to handle backing device failure like how the cache device
failure is handled,
- Add a error counter 'io_errors' and error limit 'error_limit' in struct
  cached_dev. Add another io_disable to struct cached_dev to disable I/Os
  on the problematic backing device.
- When I/O error happens on backing device, increase io_errors counter. And
  if io_errors reaches error_limit, set cache_dev->io_disable to true, and
  stop the bcache device.

The result is, if backing device is broken of disconnected, and I/O errors
reach its error limit, backing device will be disabled and the associated
bcache device will be removed from system.

Changelog:
v2: remove "bcache: " prefix in pr_error(), and use correct name string to
    print out bcache device gendisk name.
v1: indeed this is new added in v2 patch set.
Signed-off-by: NColy Li <colyli@suse.de>
Reviewed-by: NHannes Reinecke <hare@suse.com>
Reviewed-by: NMichael Lyle <mlyle@lyle.org>
Cc: Michael Lyle <mlyle@lyle.org>
Cc: Junhui Tang <tang.junhui@zte.com.cn>
Signed-off-by: NJens Axboe <axboe@kernel.dk>