bcache: Silence memcpy() run-time false positive warnings

struct bkey has internal padding in a union, but it isn't always named
the same (e.g. key ## _pad, key_p, etc). This makes it extremely hard

bcache: Silence memcpy() run-time false positive warnings

struct bkey has internal padding in a union, but it isn't always named
the same (e.g. key ## _pad, key_p, etc). This makes it extremely hard
for the compiler to reason about the available size of copies done
against such keys. Use unsafe_memcpy() for now, to silence the many
run-time false positive warnings:

memcpy: detected field-spanning write (size 264) of single field "&i->j" at drivers/md/bcache/journal.c:152 (size 240)
memcpy: detected field-spanning write (size 24) of single field "&b->key" at drivers/md/bcache/btree.c:939 (size 16)
memcpy: detected field-spanning write (size 24) of single field "&temp.key" at drivers/md/bcache/extents.c:428 (size 16)

Reported-by: Alexandre Pereira <alexpereira@disroot.org>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=216785
Acked-by: Coly Li <colyli@suse.de>
Cc: Kent Overstreet <kent.overstreet@gmail.com>
Cc: linux-bcache@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20230106060229.never.047-kees@kernel.org

show more ...

bcache: avoid journal no-space deadlock by reserving 1 journal bucket

The journal no-space deadlock was reported time to time. Such deadlock
can happen in the following situation.

When all journal

bcache: avoid journal no-space deadlock by reserving 1 journal bucket

The journal no-space deadlock was reported time to time. Such deadlock
can happen in the following situation.

When all journal buckets are fully filled by active jset with heavy
write I/O load, the cache set registration (after a reboot) will load
all active jsets and inserting them into the btree again (which is
called journal replay). If a journaled bkey is inserted into a btree
node and results btree node split, new journal request might be
triggered. For example, the btree grows one more level after the node
split, then the root node record in cache device super block will be
upgrade by bch_journal_meta() from bch_btree_set_root(). But there is no
space in journal buckets, the journal replay has to wait for new journal
bucket to be reclaimed after at least one journal bucket replayed. This
is one example that how the journal no-space deadlock happens.

The solution to avoid the deadlock is to reserve 1 journal bucket in
run time, and only permit the reserved journal bucket to be used during
cache set registration procedure for things like journal replay. Then
the journal space will never be fully filled, there is no chance for
journal no-space deadlock to happen anymore.

This patch adds a new member "bool do_reserve" in struct journal, it is
inititalized to 0 (false) when struct journal is allocated, and set to
1 (true) by bch_journal_space_reserve() when all initialization done in
run_cache_set(). In the run time when journal_reclaim() tries to
allocate a new journal bucket, free_journal_buckets() is called to check
whether there are enough free journal buckets to use. If there is only
1 free journal bucket and journal->do_reserve is 1 (true), the last
bucket is reserved and free_journal_buckets() will return 0 to indicate
no free journal bucket. Then journal_reclaim() will give up, and try
next time to see whetheer there is free journal bucket to allocate. By
this method, there is always 1 jouranl bucket reserved in run time.

During the cache set registration, journal->do_reserve is 0 (false), so
the reserved journal bucket can be used to avoid the no-space deadlock.

Reported-by: Nikhil Kshirsagar <nkshirsagar@gmail.com>
Signed-off-by: Coly Li <colyli@suse.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20220524102336.10684-5-colyli@suse.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

show more ...

bcache: put bch_bio_map() back to correct location in journal_write_unlocked()

Commit a7c50c940477 ("block: pass a block_device and opf to bio_reset")
moves bch_bio_map() inside journal_write_unlock

bcache: put bch_bio_map() back to correct location in journal_write_unlocked()

Commit a7c50c940477 ("block: pass a block_device and opf to bio_reset")
moves bch_bio_map() inside journal_write_unlocked() next to the location
where the modified bio_reset() was called.

This change is wrong because calling bch_bio_map() immediately after
bio_reset(), a BUG_ON(!bio->bi_iter.bi_size) inside bch_bio_map() will
be triggered and panic the kernel.

This patch puts bch_bio_map() back to its original correct location in
journal_write_unlocked() and avoid the BUG_ON().

Fixes: a7c50c940477 ("block: pass a block_device and opf to bio_reset")
Signed-off-by: Coly Li <colyli@suse.de>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20220419160425.4148-2-colyli@suse.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

show more ...

block: pass a block_device and opf to bio_reset

Pass the block_device that we plan to use this bio for and the
operation to bio_reset to optimize the assigment. A NULL block_device
can be passed, b

block: pass a block_device and opf to bio_reset

Pass the block_device that we plan to use this bio for and the
operation to bio_reset to optimize the assigment. A NULL block_device
can be passed, both for the passthrough case on a raw request_queue and
to temporarily avoid refactoring some nasty code.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20220124091107.642561-20-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

show more ...

block: pass a block_device and opf to bio_init

Pass the block_device that we plan to use this bio for and the
operation to bio_init to optimize the assignment. A NULL block_device
can be passed, bo

block: pass a block_device and opf to bio_init

Pass the block_device that we plan to use this bio for and the
operation to bio_init to optimize the assignment. A NULL block_device
can be passed, both for the passthrough case on a raw request_queue and
to temporarily avoid refactoring some nasty code.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20220124091107.642561-19-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

show more ...

bcache: avoid journal no-space deadlock by reserving 1 journal bucket

commit 32feee36c30ea06e38ccb8ae6e5c44c6eec790a6 upstream.

The journal no-space deadlock was reported time to time. Such deadloc

bcache: avoid journal no-space deadlock by reserving 1 journal bucket

commit 32feee36c30ea06e38ccb8ae6e5c44c6eec790a6 upstream.

The journal no-space deadlock was reported time to time. Such deadlock
can happen in the following situation.

When all journal buckets are fully filled by active jset with heavy
write I/O load, the cache set registration (after a reboot) will load
all active jsets and inserting them into the btree again (which is
called journal replay). If a journaled bkey is inserted into a btree
node and results btree node split, new journal request might be
triggered. For example, the btree grows one more level after the node
split, then the root node record in cache device super block will be
upgrade by bch_journal_meta() from bch_btree_set_root(). But there is no
space in journal buckets, the journal replay has to wait for new journal
bucket to be reclaimed after at least one journal bucket replayed. This
is one example that how the journal no-space deadlock happens.

The solution to avoid the deadlock is to reserve 1 journal bucket in
run time, and only permit the reserved journal bucket to be used during
cache set registration procedure for things like journal replay. Then
the journal space will never be fully filled, there is no chance for
journal no-space deadlock to happen anymore.

This patch adds a new member "bool do_reserve" in struct journal, it is
inititalized to 0 (false) when struct journal is allocated, and set to
1 (true) by bch_journal_space_reserve() when all initialization done in
run_cache_set(). In the run time when journal_reclaim() tries to
allocate a new journal bucket, free_journal_buckets() is called to check
whether there are enough free journal buckets to use. If there is only
1 free journal bucket and journal->do_reserve is 1 (true), the last
bucket is reserved and free_journal_buckets() will return 0 to indicate
no free journal bucket. Then journal_reclaim() will give up, and try
next time to see whetheer there is free journal bucket to allocate. By
this method, there is always 1 jouranl bucket reserved in run time.

During the cache set registration, journal->do_reserve is 0 (false), so
the reserved journal bucket can be used to avoid the no-space deadlock.

Reported-by: Nikhil Kshirsagar <nkshirsagar@gmail.com>
Signed-off-by: Coly Li <colyli@suse.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20220524102336.10684-5-colyli@suse.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

show more ...

bcache: avoid journal no-space deadlock by reserving 1 journal bucket

commit 32feee36c30ea06e38ccb8ae6e5c44c6eec790a6 upstream.

The journal no-space deadlock was reported time to time. Such deadloc

bcache: avoid journal no-space deadlock by reserving 1 journal bucket

commit 32feee36c30ea06e38ccb8ae6e5c44c6eec790a6 upstream.

The journal no-space deadlock was reported time to time. Such deadlock
can happen in the following situation.

When all journal buckets are fully filled by active jset with heavy
write I/O load, the cache set registration (after a reboot) will load
all active jsets and inserting them into the btree again (which is
called journal replay). If a journaled bkey is inserted into a btree
node and results btree node split, new journal request might be
triggered. For example, the btree grows one more level after the node
split, then the root node record in cache device super block will be
upgrade by bch_journal_meta() from bch_btree_set_root(). But there is no
space in journal buckets, the journal replay has to wait for new journal
bucket to be reclaimed after at least one journal bucket replayed. This
is one example that how the journal no-space deadlock happens.

The solution to avoid the deadlock is to reserve 1 journal bucket in
run time, and only permit the reserved journal bucket to be used during
cache set registration procedure for things like journal replay. Then
the journal space will never be fully filled, there is no chance for
journal no-space deadlock to happen anymore.

This patch adds a new member "bool do_reserve" in struct journal, it is
inititalized to 0 (false) when struct journal is allocated, and set to
1 (true) by bch_journal_space_reserve() when all initialization done in
run_cache_set(). In the run time when journal_reclaim() tries to
allocate a new journal bucket, free_journal_buckets() is called to check
whether there are enough free journal buckets to use. If there is only
1 free journal bucket and journal->do_reserve is 1 (true), the last
bucket is reserved and free_journal_buckets() will return 0 to indicate
no free journal bucket. Then journal_reclaim() will give up, and try
next time to see whetheer there is free journal bucket to allocate. By
this method, there is always 1 jouranl bucket reserved in run time.

During the cache set registration, journal->do_reserve is 0 (false), so
the reserved journal bucket can be used to avoid the no-space deadlock.

Reported-by: Nikhil Kshirsagar <nkshirsagar@gmail.com>
Signed-off-by: Coly Li <colyli@suse.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20220524102336.10684-5-colyli@suse.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

show more ...

md: bcache: Trivial typo fixes in the file journal.c

s/condidate/candidate/
s/folowing/following/

Signed-off-by: Bhaskar Chowdhury <unixbhaskar@gmail.com>
Signed-off-by: Coly Li <colyli@suse.de>
Li

md: bcache: Trivial typo fixes in the file journal.c

s/condidate/candidate/
s/folowing/following/

Signed-off-by: Bhaskar Chowdhury <unixbhaskar@gmail.com>
Signed-off-by: Coly Li <colyli@suse.de>
Link: https://lore.kernel.org/r/20210411134316.80274-6-colyli@suse.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

show more ...

bcache: remove PTR_CACHE

Remove the PTR_CACHE inline and replace it with a direct dereference
of c->cache.

(Coly Li: fix the typo from PTR_BUCKET to PTR_CACHE in commit log)

Signed-off-by: Christo

bcache: remove PTR_CACHE

Remove the PTR_CACHE inline and replace it with a direct dereference
of c->cache.

(Coly Li: fix the typo from PTR_BUCKET to PTR_CACHE in commit log)

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Coly Li <colyli@suse.de>
Link: https://lore.kernel.org/r/20210411134316.80274-3-colyli@suse.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

show more ...

bcache: Move journal work to new flush wq

This is potentially long running and not latency sensitive, let's get
it out of the way of other latency sensitive events.

As observed in the previous comm

bcache: Move journal work to new flush wq

This is potentially long running and not latency sensitive, let's get
it out of the way of other latency sensitive events.

As observed in the previous commit, the `system_wq` comes easily
congested by bcache, and this fixes a few more stalls I was observing
every once in a while.

Let's not make this `WQ_MEM_RECLAIM` as it showed to reduce performance
of boot and file system operations in my tests. Also, without
`WQ_MEM_RECLAIM`, I no longer see desktop stalls. This matches the
previous behavior as `system_wq` also does no memory reclaim:

> // workqueue.c:
> system_wq = alloc_workqueue("events", 0, 0);

Cc: Coly Li <colyli@suse.de>
Cc: stable@vger.kernel.org # 5.4+
Signed-off-by: Kai Krakow <kai@kaishome.de>
Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

show more ...

bcache: Move journal work to new flush wq

commit afe78ab46f638ecdf80a35b122ffc92c20d9ae5d upstream.

This is potentially long running and not latency sensitive, let's get
it out of the way of other

bcache: Move journal work to new flush wq

commit afe78ab46f638ecdf80a35b122ffc92c20d9ae5d upstream.

This is potentially long running and not latency sensitive, let's get
it out of the way of other latency sensitive events.

As observed in the previous commit, the `system_wq` comes easily
congested by bcache, and this fixes a few more stalls I was observing
every once in a while.

Let's not make this `WQ_MEM_RECLAIM` as it showed to reduce performance
of boot and file system operations in my tests. Also, without
`WQ_MEM_RECLAIM`, I no longer see desktop stalls. This matches the
previous behavior as `system_wq` also does no memory reclaim:

> // workqueue.c:
> system_wq = alloc_workqueue("events", 0, 0);

Cc: Coly Li <colyli@suse.de>
Cc: stable@vger.kernel.org # 5.4+
Signed-off-by: Kai Krakow <kai@kaishome.de>
Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

show more ...

bcache: remove embedded struct cache_sb from struct cache_set

Since bcache code was merged into mainline kerrnel, each cache set only
as one single cache in it. The multiple caches framework is here

bcache: remove embedded struct cache_sb from struct cache_set

Since bcache code was merged into mainline kerrnel, each cache set only
as one single cache in it. The multiple caches framework is here but the
code is far from completed. Considering the multiple copies of cached
data can also be stored on e.g. md raid1 devices, it is unnecessary to
support multiple caches in one cache set indeed.

The previous preparation patches fix the dependencies of explicitly
making a cache set only have single cache. Now we don't have to maintain
an embedded partial super block in struct cache_set, the in-memory super
block can be directly referenced from struct cache.

This patch removes the embedded struct cache_sb from struct cache_set,
and fixes all locations where the superb lock was referenced from this
removed super block by referencing the in-memory super block of struct
cache.

Signed-off-by: Coly Li <colyli@suse.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

show more ...

bcache: check and set sync status on cache's in-memory super block

Currently the cache's sync status is checked and set on cache set's in-
memory partial super block. After removing the embedded str

bcache: check and set sync status on cache's in-memory super block

Currently the cache's sync status is checked and set on cache set's in-
memory partial super block. After removing the embedded struct cache_sb
from cache set and reference cache's in-memory super block from struct
cache_set, the sync status can set and check directly on cache's super
block.

This patch checks and sets the cache sync status directly on cache's
in-memory super block. This is a preparation for later removing embedded
struct cache_sb from struct cache_set.

Signed-off-by: Coly Li <colyli@suse.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

show more ...

bcache: only use block_bytes() on struct cache

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 embed

bcache: only use block_bytes() on struct cache

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: Coly Li <colyli@suse.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

show more ...

bcache: remove for_each_cache()

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 m

bcache: remove for_each_cache()

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: Coly Li <colyli@suse.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

show more ...

treewide: Use fallthrough pseudo-keyword

Replace the existing /* fall through */ comments and its variants with
the new pseudo-keyword macro fallthrough[1]. Also, remove unnecessary
fall-through mar

treewide: Use fallthrough pseudo-keyword

Replace the existing /* fall through */ comments and its variants with
the new pseudo-keyword macro fallthrough[1]. Also, remove unnecessary
fall-through markings when it is the case.

[1] https://www.kernel.org/doc/html/v5.7/process/deprecated.html?highlight=fallthrough#implicit-switch-case-fall-through

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

show more ...

bcache: journel: use for_each_clear_bit() to simplify the code

Using for_each_clear_bit() to simplify the code.

Signed-off-by: Xu Wang <vulab@iscas.ac.cn>
Signed-off-by: Coly Li <colyli@suse.de>
Si

bcache: journel: use for_each_clear_bit() to simplify the code

Using for_each_clear_bit() to simplify the code.

Signed-off-by: Xu Wang <vulab@iscas.ac.cn>
Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

show more ...

bcache: allocate meta data pages as compound pages

There are some meta data of bcache are allocated by multiple pages,
and they are used as bio bv_page for I/Os to the cache device. for
example cach

bcache: allocate meta data pages as compound pages

There are some meta data of bcache are allocated by multiple pages,
and they are used as bio bv_page for I/Os to the cache device. for
example cache_set->uuids, cache->disk_buckets, journal_write->data,
bset_tree->data.

For such meta data memory, all the allocated pages should be treated
as a single memory block. Then the memory management and underlying I/O
code can treat them more clearly.

This patch adds __GFP_COMP flag to all the location allocating >0 order
pages for the above mentioned meta data. Then their pages are treated
as compound pages now.

Signed-off-by: Coly Li <colyli@suse.de>
Cc: stable@vger.kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

show more ...

bcache: Convert pr_<level> uses to a more typical style

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

bcache: Convert pr_<level> uses to a more typical style

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: 6ae63e3501c4 ("bcache: replace printk() by pr_*() routines")

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

show more ...

bcache: remove macro nr_to_fifo_front()

Macro nr_to_fifo_front() is only used once in btree_flush_write(),
it is unncessary indeed. This patch removes this macro and does
calculation directly in pla

bcache: remove macro nr_to_fifo_front()

Macro nr_to_fifo_front() is only used once in btree_flush_write(),
it is unncessary indeed. This patch removes this macro and does
calculation directly in place.

Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

show more ...

bcache: fix incorrect data type usage in btree_flush_write()

Dan Carpenter points out that from commit 2aa8c529387c ("bcache: avoid
unnecessary btree nodes flushing in btree_flush_write()"), there i

bcache: fix incorrect data type usage in btree_flush_write()

Dan Carpenter points out that from commit 2aa8c529387c ("bcache: avoid
unnecessary btree nodes flushing in btree_flush_write()"), there is a
incorrect data type usage which leads to the following static checker
warning:
drivers/md/bcache/journal.c:444 btree_flush_write()
warn: 'ref_nr' unsigned <= 0

drivers/md/bcache/journal.c
422 static void btree_flush_write(struct cache_set *c)
423 {
424 struct btree *b, *t, *btree_nodes[BTREE_FLUSH_NR];
425 unsigned int i, nr, ref_nr;
^^^^^^

426 atomic_t *fifo_front_p, *now_fifo_front_p;
427 size_t mask;
428
429 if (c->journal.btree_flushing)
430 return;
431
432 spin_lock(&c->journal.flush_write_lock);
433 if (c->journal.btree_flushing) {
434 spin_unlock(&c->journal.flush_write_lock);
435 return;
436 }
437 c->journal.btree_flushing = true;
438 spin_unlock(&c->journal.flush_write_lock);
439
440 /* get the oldest journal entry and check its refcount */
441 spin_lock(&c->journal.lock);
442 fifo_front_p = &fifo_front(&c->journal.pin);
443 ref_nr = atomic_read(fifo_front_p);
444 if (ref_nr <= 0) {
^^^^^^^^^^^
Unsigned can't be less than zero.

445 /*
446 * do nothing if no btree node references
447 * the oldest journal entry
448 */
449 spin_unlock(&c->journal.lock);
450 goto out;
451 }
452 spin_unlock(&c->journal.lock);

As the warning information indicates, local varaible ref_nr in unsigned
int type is wrong, which does not matche atomic_read() and the "<= 0"
checking.

This patch fixes the above error by defining local variable ref_nr as
int type.

Fixes: 2aa8c529387c ("bcache: avoid unnecessary btree nodes flushing in btree_flush_write()")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

show more ...

bcache: avoid unnecessary btree nodes flushing in btree_flush_write()

the commit 91be66e1318f ("bcache: performance improvement for
btree_flush_write()") was an effort to flushing btree node with ol

bcache: avoid unnecessary btree nodes flushing in btree_flush_write()

the commit 91be66e1318f ("bcache: performance improvement for
btree_flush_write()") was an effort to flushing btree node with oldest
btree node faster in following methods,
- Only iterate dirty btree nodes in c->btree_cache, avoid scanning a lot
of clean btree nodes.
- Take c->btree_cache as a LRU-like list, aggressively flushing all
dirty nodes from tail of c->btree_cache util the btree node with
oldest journal entry is flushed. This is to reduce the time of holding
c->bucket_lock.

Guoju Fang and Shuang Li reported that they observe unexptected extra
write I/Os on cache device after applying the above patch. Guoju Fang
provideed more detailed diagnose information that the aggressive
btree nodes flushing may cause 10x more btree nodes to flush in his
workload. He points out when system memory is large enough to hold all
btree nodes in memory, c->btree_cache is not a LRU-like list any more.
Then the btree node with oldest journal entry is very probably not-
close to the tail of c->btree_cache list. In such situation much more
dirty btree nodes will be aggressively flushed before the target node
is flushed. When slow SATA SSD is used as cache device, such over-
aggressive flushing behavior will cause performance regression.

After spending a lot of time on debug and diagnose, I find the real
condition is more complicated, aggressive flushing dirty btree nodes
from tail of c->btree_cache list is not a good solution.
- When all btree nodes are cached in memory, c->btree_cache is not
a LRU-like list, the btree nodes with oldest journal entry won't
be close to the tail of the list.
- There can be hundreds dirty btree nodes reference the oldest journal
entry, before flushing all the nodes the oldest journal entry cannot
be reclaimed.
When the above two conditions mixed together, a simply flushing from
tail of c->btree_cache list is really NOT a good idea.

Fortunately there is still chance to make btree_flush_write() work
better. Here is how this patch avoids unnecessary btree nodes flushing,
- Only acquire c->journal.lock when getting oldest journal entry of
fifo c->journal.pin. In rested locations check the journal entries
locklessly, so their values can be changed on other cores
in parallel.
- In loop list_for_each_entry_safe_reverse(), checking latest front
point of fifo c->journal.pin. If it is different from the original
point which we get with locking c->journal.lock, it means the oldest
journal entry is reclaim on other cores. At this moment, all selected
dirty nodes recorded in array btree_nodes[] are all flushed and clean
on other CPU cores, it is unncessary to iterate c->btree_cache any
longer. Just quit the list_for_each_entry_safe_reverse() loop and
the following for-loop will skip all the selected clean nodes.
- Find a proper time to quit the list_for_each_entry_safe_reverse()
loop. Check the refcount value of orignial fifo front point, if the
value is larger than selected node number of btree_nodes[], it means
more matching btree nodes should be scanned. Otherwise it means no
more matching btee nodes in rest of c->btree_cache list, the loop
can be quit. If the original oldest journal entry is reclaimed and
fifo front point is updated, the refcount of original fifo front point
will be 0, then the loop will be quit too.
- Not hold c->bucket_lock too long time. c->bucket_lock is also required
for space allocation for cached data, hold it for too long time will
block regular I/O requests. When iterating list c->btree_cache, even
there are a lot of maching btree nodes, in order to not holding
c->bucket_lock for too long time, only BTREE_FLUSH_NR nodes are
selected and to flush in following for-loop.
With this patch, only btree nodes referencing oldest journal entry
are flushed to cache device, no aggressive flushing for unnecessary
btree node any more. And in order to avoid blocking regluar I/O
requests, each time when btree_flush_write() called, at most only
BTREE_FLUSH_NR btree nodes are selected to flush, even there are more
maching btree nodes in list c->btree_cache.

At last, one more thing to explain: Why it is safe to read front point
of c->journal.pin without holding c->journal.lock inside the
list_for_each_entry_safe_reverse() loop ?

Here is my answer: When reading the front point of fifo c->journal.pin,
we don't need to know the exact value of front point, we just want to
check whether the value is different from the original front point
(which is accurate value because we get it while c->jouranl.lock is
held). For such purpose, it works as expected without holding
c->journal.lock. Even the front point is changed on other CPU core and
not updated to local core, and current iterating btree node has
identical journal entry local as original fetched fifo front point, it
is still safe. Because after holding mutex b->write_lock (with memory
barrier) this btree node can be found as clean and skipped, the loop
will quite latter when iterate on next node of list c->btree_cache.

Fixes: 91be66e1318f ("bcache: performance improvement for btree_flush_write()")
Reported-by: Guoju Fang <fangguoju@gmail.com>
Reported-by: Shuang Li <psymon@bonuscloud.io>
Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

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bcache: add reclaimed_journal_buckets to struct cache_set

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 man

bcache: add reclaimed_journal_buckets to struct cache_set

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: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

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bcache: performance improvement for btree_flush_write()

This patch improves performance for btree_flush_write() in following
ways,
- Use another spinlock journal.flush_write_lock to replace the very

bcache: performance improvement for btree_flush_write()

This patch improves performance for btree_flush_write() in following
ways,
- Use another spinlock journal.flush_write_lock to replace the very
hot journal.lock. We don't have to use journal.lock here, selecting
candidate btree nodes takes a lot of time, hold journal.lock here will
block other jouranling threads and drop the overall I/O performance.
- Only select flushing btree node from c->btree_cache list. When the
machine has a large system memory, mca cache may have a huge number of
cached btree nodes. Iterating all the cached nodes will take a lot
of CPU time, and most of the nodes on c->btree_cache_freeable and
c->btree_cache_freed lists are cleared and have need to flush. So only
travel mca list c->btree_cache to select flushing btree node should be
enough for most of the cases.
- Don't iterate whole c->btree_cache list, only reversely select first
BTREE_FLUSH_NR btree nodes to flush. Iterate all btree nodes from
c->btree_cache and select the oldest journal pin btree nodes consumes
huge number of CPU cycles if the list is huge (push and pop a node
into/out of a heap is expensive). The last several dirty btree nodes
on the tail of c->btree_cache list are earlest allocated and cached
btree nodes, they are relative to the oldest journal pin btree nodes.
Therefore only flushing BTREE_FLUSH_NR btree nodes from tail of
c->btree_cache probably includes the oldest journal pin btree nodes.

In my testing, the above change decreases 50%+ CPU consumption when
journal space is full. Some times IOPS drops to 0 for 5-8 seconds,
comparing blocking I/O for 120+ seconds in previous code, this is much
better. Maybe there is room to improve in future, but at this momment
the fix looks fine and performs well in my testing.

Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

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bcache: fix race in btree_flush_write()

There is a race between mca_reap(), btree_node_free() and journal code
btree_flush_write(), which results very rare and strange deadlock or
panic and are very

bcache: fix race in btree_flush_write()

There is a race between mca_reap(), btree_node_free() and journal code
btree_flush_write(), which results very rare and strange deadlock or
panic and are very hard to reproduce.

Let me explain how the race happens. In btree_flush_write() one btree
node with oldest journal pin is selected, then it is flushed to cache
device, the select-and-flush is a two steps operation. Between these two
steps, there are something may happen inside the race window,
- The selected btree node was reaped by mca_reap() and allocated to
other requesters for other btree node.
- The slected btree node was selected, flushed and released by mca
shrink callback bch_mca_scan().
When btree_flush_write() tries to flush the selected btree node, firstly
b->write_lock is held by mutex_lock(). If the race happens and the
memory of selected btree node is allocated to other btree node, if that
btree node's write_lock is held already, a deadlock very probably
happens here. A worse case is the memory of the selected btree node is
released, then all references to this btree node (e.g. b->write_lock)
will trigger NULL pointer deference panic.

This race was introduced in commit cafe56359144 ("bcache: A block layer
cache"), and enlarged by commit c4dc2497d50d ("bcache: fix high CPU
occupancy during journal"), which selected 128 btree nodes and flushed
them one-by-one in a quite long time period.

Such race is not easy to reproduce before. On a Lenovo SR650 server with
48 Xeon cores, and configure 1 NVMe SSD as cache device, a MD raid0
device assembled by 3 NVMe SSDs as backing device, this race can be
observed around every 10,000 times btree_flush_write() gets called. Both
deadlock and kernel panic all happened as aftermath of the race.

The idea of the fix is to add a btree flag BTREE_NODE_journal_flush. It
is set when selecting btree nodes, and cleared after btree nodes
flushed. Then when mca_reap() selects a btree node with this bit set,
this btree node will be skipped. Since mca_reap() only reaps btree node
without BTREE_NODE_journal_flush flag, such race is avoided.

Once corner case should be noticed, that is btree_node_free(). It might
be called in some error handling code path. For example the following
code piece from btree_split(),
2149 err_free2:
2150 bkey_put(b->c, &n2->key);
2151 btree_node_free(n2);
2152 rw_unlock(true, n2);
2153 err_free1:
2154 bkey_put(b->c, &n1->key);
2155 btree_node_free(n1);
2156 rw_unlock(true, n1);
At line 2151 and 2155, the btree node n2 and n1 are released without
mac_reap(), so BTREE_NODE_journal_flush also needs to be checked here.
If btree_node_free() is called directly in such error handling path,
and the selected btree node has BTREE_NODE_journal_flush bit set, just
delay for 1 us and retry again. In this case this btree node won't
be skipped, just retry until the BTREE_NODE_journal_flush bit cleared,
and free the btree node memory.

Fixes: cafe56359144 ("bcache: A block layer cache")
Signed-off-by: Coly Li <colyli@suse.de>
Reported-and-tested-by: kbuild test robot <lkp@intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

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