linux-stable.git/drivers/md/bcache, branch v6.16.2

bcache: remove unnecessary select MIN_HEAP

2025-06-20T03:48:03+00:00

After reverting the transition to the generic min heap library, bcache no
longer depends on MIN_HEAP.  The select entry can be removed to reduce
code size and shrink the kernel's attack surface.

This change effectively reverts the bcache-related part of commit
92a8b224b833 ("lib/min_heap: introduce non-inline versions of min heap API
functions").

This is part of a series of changes to address a performance regression
caused by the use of the generic min_heap implementation.

As reported by Robert, bcache now suffers from latency spikes, with P100
(max) latency increasing from 600 ms to 2.4 seconds every 5 minutes. 
These regressions degrade bcache's effectiveness as a low-latency cache
layer and lead to frequent timeouts and application stalls in production
environments.

Link: https://lore.kernel.org/lkml/CAJhEC05+0S69z+3+FB2Cd0hD+pCRyWTKLEOsc8BOmH73p1m+KQ@mail.gmail.com
Link: https://lkml.kernel.org/r/20250614202353.1632957-4-visitorckw@gmail.com
Fixes: 866898efbb25 ("bcache: remove heap-related macros and switch to generic min_heap")
Fixes: 92a8b224b833 ("lib/min_heap: introduce non-inline versions of min heap API functions")
Signed-off-by: Kuan-Wei Chiu 
Reported-by: Robert Pang 
Closes: https://lore.kernel.org/linux-bcache/CAJhEC06F_AtrPgw2-7CvCqZgeStgCtitbD-ryuPpXQA-JG5XXw@mail.gmail.com
Acked-by: Coly Li 
Cc: Ching-Chun (Jim) Huang 
Cc: Kent Overstreet 
Cc: 
Signed-off-by: Andrew Morton

Revert "bcache: remove heap-related macros and switch to generic min_heap"

2025-06-20T03:48:03+00:00

This reverts commit 866898efbb25bb44fd42848318e46db9e785973a.

The generic bottom-up min_heap implementation causes performance
regression in invalidate_buckets_lru(), a hot path in bcache.  Before the
cache is fully populated, new_bucket_prio() often returns zero, leading to
many equal comparisons.  In such cases, bottom-up sift_down performs up to
2 * log2(n) comparisons, while the original top-down approach completes
with just O() comparisons, resulting in a measurable performance gap.

The performance degradation is further worsened by the non-inlined
min_heap API functions introduced in commit 92a8b224b833 ("lib/min_heap:
introduce non-inline versions of min heap API functions"), adding function
call overhead to this critical path.

As reported by Robert, bcache now suffers from latency spikes, with P100
(max) latency increasing from 600 ms to 2.4 seconds every 5 minutes. 
These regressions degrade bcache's effectiveness as a low-latency cache
layer and lead to frequent timeouts and application stalls in production
environments.

This revert aims to restore bcache's original low-latency behavior.

Link: https://lore.kernel.org/lkml/CAJhEC05+0S69z+3+FB2Cd0hD+pCRyWTKLEOsc8BOmH73p1m+KQ@mail.gmail.com
Link: https://lkml.kernel.org/r/20250614202353.1632957-3-visitorckw@gmail.com
Fixes: 866898efbb25 ("bcache: remove heap-related macros and switch to generic min_heap")
Fixes: 92a8b224b833 ("lib/min_heap: introduce non-inline versions of min heap API functions")
Signed-off-by: Kuan-Wei Chiu 
Reported-by: Robert Pang 
Closes: https://lore.kernel.org/linux-bcache/CAJhEC06F_AtrPgw2-7CvCqZgeStgCtitbD-ryuPpXQA-JG5XXw@mail.gmail.com
Acked-by: Coly Li 
Cc: Ching-Chun (Jim) Huang 
Cc: Kent Overstreet 
Cc: 
Signed-off-by: Andrew Morton

Revert "bcache: update min_heap_callbacks to use default builtin swap"

2025-06-20T03:48:02+00:00

Patch series "bcache: Revert min_heap migration due to performance
regression".

This patch series reverts the migration of bcache from its original heap
implementation to the generic min_heap library.  While the original change
aimed to simplify the code and improve maintainability, it introduced a
severe performance regression in real-world scenarios.

As reported by Robert, systems using bcache now suffer from periodic
latency spikes, with P100 (max) latency increasing from 600 ms to 2.4
seconds every 5 minutes.  This degrades bcache's value as a low-latency
caching layer, and leads to frequent timeouts and application stalls in
production environments.

The primary cause of this regression is the behavior of the generic
min_heap implementation's bottom-up sift_down, which performs up to 2 *
log2(n) comparisons when many elements are equal.  The original top-down
variant used by bcache only required O(1) comparisons in such cases.  The
issue was further exacerbated by commit 92a8b224b833 ("lib/min_heap:
introduce non-inline versions of min heap API functions"), which
introduced non-inlined versions of the min_heap API, adding function call
overhead to a performance-critical hot path.


This patch (of 3):

This reverts commit 3d8a9a1c35227c3f1b0bd132c9f0a80dbda07b65.

Although removing the custom swap function simplified the code, this
change is part of a broader migration to the generic min_heap API that
introduced significant performance regressions in bcache.

As reported by Robert, bcache now suffers from latency spikes, with P100
(max) latency increasing from 600 ms to 2.4 seconds every 5 minutes. 
These regressions degrade bcache's effectiveness as a low-latency cache
layer and lead to frequent timeouts and application stalls in production
environments.

This revert is part of a series of changes to restore previous performance
by undoing the min_heap transition.

Link: https://lkml.kernel.org/r/20250614202353.1632957-1-visitorckw@gmail.com
Link: https://lore.kernel.org/lkml/CAJhEC05+0S69z+3+FB2Cd0hD+pCRyWTKLEOsc8BOmH73p1m+KQ@mail.gmail.com
Link: https://lkml.kernel.org/r/20250614202353.1632957-2-visitorckw@gmail.com
Fixes: 866898efbb25 ("bcache: remove heap-related macros and switch to generic min_heap")
Fixes: 92a8b224b833 ("lib/min_heap: introduce non-inline versions of min heap API functions")
Signed-off-by: Kuan-Wei Chiu 
Reported-by: Robert Pang 
Closes: https://lore.kernel.org/linux-bcache/CAJhEC06F_AtrPgw2-7CvCqZgeStgCtitbD-ryuPpXQA-JG5XXw@mail.gmail.com
Acked-by: Coly Li 
Cc: Ching-Chun (Jim) Huang 
Cc: Kent Overstreet 
Cc: 
Signed-off-by: Andrew Morton

treewide, timers: Rename from_timer() to timer_container_of()

2025-06-08T07:07:37+00:00

Move this API to the canonical timer_*() namespace.

[ tglx: Redone against pre rc1 ]

Signed-off-by: Ingo Molnar 
Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/all/aB2X0jCKQO56WdMt@gmail.com

Merge tag 'block-6.16-20250606' of git://git.kernel.dk/linux

2025-06-06T20:12:50+00:00

Pull more block updates from Jens Axboe:

 - NVMe pull request via Christoph:
      - TCP error handling fix (Shin'ichiro Kawasaki)
      - TCP I/O stall handling fixes (Hannes Reinecke)
      - fix command limits status code (Keith Busch)
      - support vectored buffers also for passthrough (Pavel Begunkov)
      - spelling fixes (Yi Zhang)

 - MD pull request via Yu:
      - fix REQ_RAHEAD and REQ_NOWAIT IO err handling for raid1/10
      - fix max_write_behind setting for dm-raid
      - some minor cleanups

 - Integrity data direction fix and cleanup

 - bcache NULL pointer fix

 - Fix for loop missing write start/end handling

 - Decouple hardware queues and IO threads in ublk

 - Slew of ublk selftests additions and updates

* tag 'block-6.16-20250606' of git://git.kernel.dk/linux: (29 commits)
  nvme: spelling fixes
  nvme-tcp: fix I/O stalls on congested sockets
  nvme-tcp: sanitize request list handling
  nvme-tcp: remove tag set when second admin queue config fails
  nvme: enable vectored registered bufs for passthrough cmds
  nvme: fix implicit bool to flags conversion
  nvme: fix command limits status code
  selftests: ublk: kublk: improve behavior on init failure
  block: flip iter directions in blk_rq_integrity_map_user()
  block: drop direction param from bio_integrity_copy_user()
  selftests: ublk: cover PER_IO_DAEMON in more stress tests
  Documentation: ublk: document UBLK_F_PER_IO_DAEMON
  selftests: ublk: add stress test for per io daemons
  selftests: ublk: add functional test for per io daemons
  selftests: ublk: kublk: decouple ublk_queues from ublk server threads
  selftests: ublk: kublk: move per-thread data out of ublk_queue
  selftests: ublk: kublk: lift queue initialization out of thread
  selftests: ublk: kublk: tie sqe allocation to io instead of queue
  selftests: ublk: kublk: plumb q_id in io_uring user_data
  ublk: have a per-io daemon instead of a per-queue daemon
  ...

Merge tag 'mm-nonmm-stable-2025-05-31-15-28' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

2025-06-01T02:12:53+00:00

Pull non-MM updates from Andrew Morton:

 - "hung_task: extend blocking task stacktrace dump to semaphore" from
   Lance Yang enhances the hung task detector.

   The detector presently dumps the blocking tasks's stack when it is
   blocked on a mutex. Lance's series extends this to semaphores

 - "nilfs2: improve sanity checks in dirty state propagation" from
   Wentao Liang addresses a couple of minor flaws in nilfs2

 - "scripts/gdb: Fixes related to lx_per_cpu()" from Illia Ostapyshyn
   fixes a couple of issues in the gdb scripts

 - "Support kdump with LUKS encryption by reusing LUKS volume keys" from
   Coiby Xu addresses a usability problem with kdump.

   When the dump device is LUKS-encrypted, the kdump kernel may not have
   the keys to the encrypted filesystem. A full writeup of this is in
   the series [0/N] cover letter

 - "sysfs: add counters for lockups and stalls" from Max Kellermann adds
   /sys/kernel/hardlockup_count and /sys/kernel/hardlockup_count and
   /sys/kernel/rcu_stall_count

 - "fork: Page operation cleanups in the fork code" from Pasha Tatashin
   implements a number of code cleanups in fork.c

 - "scripts/gdb/symbols: determine KASLR offset on s390 during early
   boot" from Ilya Leoshkevich fixes some s390 issues in the gdb
   scripts

* tag 'mm-nonmm-stable-2025-05-31-15-28' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (67 commits)
  llist: make llist_add_batch() a static inline
  delayacct: remove redundant code and adjust indentation
  squashfs: add optional full compressed block caching
  crash_dump, nvme: select CONFIGFS_FS as built-in
  scripts/gdb/symbols: determine KASLR offset on s390 during early boot
  scripts/gdb/symbols: factor out pagination_off()
  scripts/gdb/symbols: factor out get_vmlinux()
  kernel/panic.c: format kernel-doc comments
  mailmap: update and consolidate Casey Connolly's name and email
  nilfs2: remove wbc->for_reclaim handling
  fork: define a local GFP_VMAP_STACK
  fork: check charging success before zeroing stack
  fork: clean-up naming of vm_stack/vm_struct variables in vmap stacks code
  fork: clean-up ifdef logic around stack allocation
  kernel/rcu/tree_stall: add /sys/kernel/rcu_stall_count
  kernel/watchdog: add /sys/kernel/{hard,soft}lockup_count
  x86/crash: make the page that stores the dm crypt keys inaccessible
  x86/crash: pass dm crypt keys to kdump kernel
  Revert "x86/mm: Remove unused __set_memory_prot()"
  crash_dump: retrieve dm crypt keys in kdump kernel
  ...

Merge tag 'hardening-v6.16-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

2025-05-28T14:47:10+00:00

Pull hardening updates from Kees Cook:

 - Update overflow helpers to ease refactoring of on-stack flex array
   instances (Gustavo A. R. Silva, Kees Cook)

 - lkdtm: Use SLAB_NO_MERGE instead of constructors (Harry Yoo)

 - Simplify CONFIG_CC_HAS_COUNTED_BY (Jan Hendrik Farr)

 - Disable u64 usercopy KUnit test on 32-bit SPARC (Thomas Weißschuh)

 - Add missed designated initializers now exposed by fixed randstruct
   (Nathan Chancellor, Kees Cook)

 - Document compilers versions for __builtin_dynamic_object_size

 - Remove ARM_SSP_PER_TASK GCC plugin

 - Fix GCC plugin randstruct, add selftests, and restore COMPILE_TEST
   builds

 - Kbuild: induce full rebuilds when dependencies change with GCC
   plugins, the Clang sanitizer .scl file, or the randstruct seed.

 - Kbuild: Switch from -Wvla to -Wvla-larger-than=1

 - Correct several __nonstring uses for -Wunterminated-string-initialization

* tag 'hardening-v6.16-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux: (23 commits)
  Revert "hardening: Disable GCC randstruct for COMPILE_TEST"
  lib/tests: randstruct: Add deep function pointer layout test
  lib/tests: Add randstruct KUnit test
  randstruct: gcc-plugin: Remove bogus void member
  net: qede: Initialize qede_ll_ops with designated initializer
  scsi: qedf: Use designated initializer for struct qed_fcoe_cb_ops
  md/bcache: Mark __nonstring look-up table
  integer-wrap: Force full rebuild when .scl file changes
  randstruct: Force full rebuild when seed changes
  gcc-plugins: Force full rebuild when plugins change
  kbuild: Switch from -Wvla to -Wvla-larger-than=1
  hardening: simplify CONFIG_CC_HAS_COUNTED_BY
  overflow: Fix direct struct member initialization in _DEFINE_FLEX()
  kunit/overflow: Add tests for STACK_FLEX_ARRAY_SIZE() helper
  overflow: Add STACK_FLEX_ARRAY_SIZE() helper
  input/joystick: magellan: Mark __nonstring look-up table const
  watchdog: exar: Shorten identity name to fit correctly
  mod_devicetable: Enlarge the maximum platform_device_id name length
  overflow: Clarify expectations for getting DEFINE_FLEX variable sizes
  compiler_types: Identify compiler versions for __builtin_dynamic_object_size
  ...

bcache: reserve more RESERVE_BTREE buckets to prevent allocator hang

2025-05-27T13:38:19+00:00

Reported an IO hang and unrecoverable error in our testing environment.

After careful research, we found that bch_allocator_thread is stuck,
the call stack is as follows:
[<0>] __switch_to+0xbc/0x108
[<0>] __closure_sync+0x7c/0xbc [bcache]
[<0>] bch_prio_write+0x430/0x448 [bcache]
[<0>] bch_allocator_thread+0xb44/0xb70 [bcache]
[<0>] kthread+0x124/0x130
[<0>] ret_from_fork+0x10/0x18

Moreover, the RESERVE_BTREE type bucket slot are empty and journal_full
occurs at the same time.

When the cache disk is first used, the sb.nJournal_buckets defaults to 0.
So, only 8 RESERVE_BTREE type buckets are reserved. If RESERVE_BTREE type
buckets used up or btree_check_reserve() failed when request handle btree
split, the request will be repeatedly retried and wait for alloc thread to
fill in.

After the alloc thread fills the buckets, it will call bch_prio_write().
If journal_full occurs simultaneously at this time, journal_reclaim() and
btree_flush_write() will be called sequentially, journal_write cannot be
completed.

This is a low probability event, we believe that reserve more RESERVE_BTREE
buckets can avoid the worst situation.

Fixes: 682811b3ce1a ("bcache: fix for allocator and register thread race")
Signed-off-by: Mingzhe Zou 
Signed-off-by: Coly Li 
Link: https://lore.kernel.org/r/20250527051601.74407-4-colyli@kernel.org
Signed-off-by: Jens Axboe

bcache: remove unused constants

2025-05-27T13:38:19+00:00

Remove constants MAX_NEED_GC and MAX_SAVE_PRIO in btree.c that have been unused
since initial commit.

Signed-off-by: Robert Pang 
Signed-off-by: Coly Li 
Link: https://lore.kernel.org/r/20250527051601.74407-3-colyli@kernel.org
Signed-off-by: Jens Axboe

bcache: fix NULL pointer in cache_set_flush()

2025-05-27T13:38:19+00:00

1. LINE#1794 - LINE#1887 is some codes about function of
   bch_cache_set_alloc().
2. LINE#2078 - LINE#2142 is some codes about function of
   register_cache_set().
3. register_cache_set() will call bch_cache_set_alloc() in LINE#2098.

 1794 struct cache_set *bch_cache_set_alloc(struct cache_sb *sb)
 1795 {
 ...
 1860         if (!(c->devices = kcalloc(c->nr_uuids, sizeof(void *), GFP_KERNEL)) ||
 1861             mempool_init_slab_pool(&c->search, 32, bch_search_cache) ||
 1862             mempool_init_kmalloc_pool(&c->bio_meta, 2,
 1863                                 sizeof(struct bbio) + sizeof(struct bio_vec) *
 1864                                 bucket_pages(c)) ||
 1865             mempool_init_kmalloc_pool(&c->fill_iter, 1, iter_size) ||
 1866             bioset_init(&c->bio_split, 4, offsetof(struct bbio, bio),
 1867                         BIOSET_NEED_BVECS|BIOSET_NEED_RESCUER) ||
 1868             !(c->uuids = alloc_bucket_pages(GFP_KERNEL, c)) ||
 1869             !(c->moving_gc_wq = alloc_workqueue("bcache_gc",
 1870                                                 WQ_MEM_RECLAIM, 0)) ||
 1871             bch_journal_alloc(c) ||
 1872             bch_btree_cache_alloc(c) ||
 1873             bch_open_buckets_alloc(c) ||
 1874             bch_bset_sort_state_init(&c->sort, ilog2(c->btree_pages)))
 1875                 goto err;
                      ^^^^^^^^
 1876
 ...
 1883         return c;
 1884 err:
 1885         bch_cache_set_unregister(c);
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 1886         return NULL;
 1887 }
 ...
 2078 static const char *register_cache_set(struct cache *ca)
 2079 {
 ...
 2098         c = bch_cache_set_alloc(&ca->sb);
 2099         if (!c)
 2100                 return err;
                      ^^^^^^^^^^
 ...
 2128         ca->set = c;
 2129         ca->set->cache[ca->sb.nr_this_dev] = ca;
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 ...
 2138         return NULL;
 2139 err:
 2140         bch_cache_set_unregister(c);
 2141         return err;
 2142 }

(1) If LINE#1860 - LINE#1874 is true, then do 'goto err'(LINE#1875) and
    call bch_cache_set_unregister()(LINE#1885).
(2) As (1) return NULL(LINE#1886), LINE#2098 - LINE#2100 would return.
(3) As (2) has returned, LINE#2128 - LINE#2129 would do *not* give the
    value to c->cache[], it means that c->cache[] is NULL.

LINE#1624 - LINE#1665 is some codes about function of cache_set_flush().
As (1), in LINE#1885 call
bch_cache_set_unregister()
---> bch_cache_set_stop()
     ---> closure_queue()
          -.-> cache_set_flush() (as below LINE#1624)

 1624 static void cache_set_flush(struct closure *cl)
 1625 {
 ...
 1654         for_each_cache(ca, c, i)
 1655                 if (ca->alloc_thread)
                          ^^
 1656                         kthread_stop(ca->alloc_thread);
 ...
 1665 }

(4) In LINE#1655 ca is NULL(see (3)) in cache_set_flush() then the
    kernel crash occurred as below:
[  846.712887] bcache: register_cache() error drbd6: cannot allocate memory
[  846.713242] bcache: register_bcache() error : failed to register device
[  846.713336] bcache: cache_set_free() Cache set 2f84bdc1-498a-4f2f-98a7-01946bf54287 unregistered
[  846.713768] BUG: unable to handle kernel NULL pointer dereference at 00000000000009f8
[  846.714790] PGD 0 P4D 0
[  846.715129] Oops: 0000 [#1] SMP PTI
[  846.715472] CPU: 19 PID: 5057 Comm: kworker/19:16 Kdump: loaded Tainted: G           OE    --------- -  - 4.18.0-147.5.1.el8_1.5es.3.x86_64 #1
[  846.716082] Hardware name: ESPAN GI-25212/X11DPL-i, BIOS 2.1 06/15/2018
[  846.716451] Workqueue: events cache_set_flush [bcache]
[  846.716808] RIP: 0010:cache_set_flush+0xc9/0x1b0 [bcache]
[  846.717155] Code: 00 4c 89 a5 b0 03 00 00 48 8b 85 68 f6 ff ff a8 08 0f 84 88 00 00 00 31 db 66 83 bd 3c f7 ff ff 00 48 8b 85 48 ff ff ff 74 28 <48> 8b b8 f8 09 00 00 48 85 ff 74 05 e8 b6 58 a2 e1 0f b7 95 3c f7
[  846.718026] RSP: 0018:ffffb56dcf85fe70 EFLAGS: 00010202
[  846.718372] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
[  846.718725] RDX: 0000000000000001 RSI: 0000000040000001 RDI: 0000000000000000
[  846.719076] RBP: ffffa0ccc0f20df8 R08: ffffa0ce1fedb118 R09: 000073746e657665
[  846.719428] R10: 8080808080808080 R11: 0000000000000000 R12: ffffa0ce1fee8700
[  846.719779] R13: ffffa0ccc0f211a8 R14: ffffa0cd1b902840 R15: ffffa0ccc0f20e00
[  846.720132] FS:  0000000000000000(0000) GS:ffffa0ce1fec0000(0000) knlGS:0000000000000000
[  846.720726] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  846.721073] CR2: 00000000000009f8 CR3: 00000008ba00a005 CR4: 00000000007606e0
[  846.721426] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  846.721778] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  846.722131] PKRU: 55555554
[  846.722467] Call Trace:
[  846.722814]  process_one_work+0x1a7/0x3b0
[  846.723157]  worker_thread+0x30/0x390
[  846.723501]  ? create_worker+0x1a0/0x1a0
[  846.723844]  kthread+0x112/0x130
[  846.724184]  ? kthread_flush_work_fn+0x10/0x10
[  846.724535]  ret_from_fork+0x35/0x40

Now, check whether that ca is NULL in LINE#1655 to fix the issue.

Signed-off-by: Linggang Zeng 
Signed-off-by: Mingzhe Zou 
Signed-off-by: Coly Li 
Link: https://lore.kernel.org/r/20250527051601.74407-2-colyli@kernel.org
Signed-off-by: Jens Axboe