kernel/linux.git/drivers/md/bcache/writeback.c, branch v6.6.132

bcache: fix variable length array abuse in btree_iter

2024-06-16T11:47:32+00:00

commit 3a861560ccb35f2a4f0a4b8207fa7c2a35fc7f31 upstream. btree_iter is used in two ways: either allocated on the stack with a fixed size MAX_BSETS, or from a mempool with a dynamic size based on the specific cache set. Previously, the struct had a fixed-length array of size MAX_BSETS which was indexed out-of-bounds for the dynamically-sized iterators, which causes UBSAN to complain. This patch uses the same approach as in bcachefs's sort_iter and splits the iterator into a btree_iter with a flexible array member and a btree_iter_stack which embeds a btree_iter as well as a fixed-length data array. Cc: stable@vger.kernel.org Closes: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2039368 Signed-off-by: Matthew Mirvish Signed-off-by: Coly Li Link: https://lore.kernel.org/r/20240509011117.2697-3-colyli@suse.de Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman

bcache: remove redundant assignment to variable cur_idx

2023-12-20T16:01:56+00:00

[ Upstream commit be93825f0e6428c2d3f03a6e4d447dc48d33d7ff ] Variable cur_idx is being initialized with a value that is never read, it is being re-assigned later in a while-loop. Remove the redundant assignment. Cleans up clang scan build warning: drivers/md/bcache/writeback.c:916:2: warning: Value stored to 'cur_idx' is never read [deadcode.DeadStores] Signed-off-by: Colin Ian King Reviewed-by: Coly Li Signed-off-by: Coly Li Link: https://lore.kernel.org/r/20231120052503.6122-4-colyli@suse.de Signed-off-by: Jens Axboe Signed-off-by: Sasha Levin

bcache: fixup lock c->root error

2023-12-03T06:33:09+00:00

commit e34820f984512b433ee1fc291417e60c47d56727 upstream. We had a problem with io hung because it was waiting for c->root to release the lock. crash> cache_set.root -l cache_set.list ffffa03fde4c0050 root = 0xffff802ef454c800 crash> btree -o 0xffff802ef454c800 | grep rw_semaphore [ffff802ef454c858] struct rw_semaphore lock; crash> struct rw_semaphore ffff802ef454c858 struct rw_semaphore { count = { counter = -4294967297 }, wait_list = { next = 0xffff00006786fc28, prev = 0xffff00005d0efac8 }, wait_lock = { raw_lock = { { val = { counter = 0 }, { locked = 0 '\000', pending = 0 '\000' }, { locked_pending = 0, tail = 0 } } } }, osq = { tail = { counter = 0 } }, owner = 0xffffa03fdc586603 } The "counter = -4294967297" means that lock count is -1 and a write lock is being attempted. Then, we found that there is a btree with a counter of 1 in btree_cache_freeable. crash> cache_set -l cache_set.list ffffa03fde4c0050 -o|grep btree_cache [ffffa03fde4c1140] struct list_head btree_cache; [ffffa03fde4c1150] struct list_head btree_cache_freeable; [ffffa03fde4c1160] struct list_head btree_cache_freed; [ffffa03fde4c1170] unsigned int btree_cache_used; [ffffa03fde4c1178] wait_queue_head_t btree_cache_wait; [ffffa03fde4c1190] struct task_struct *btree_cache_alloc_lock; crash> list -H ffffa03fde4c1140|wc -l 973 crash> list -H ffffa03fde4c1150|wc -l 1123 crash> cache_set.btree_cache_used -l cache_set.list ffffa03fde4c0050 btree_cache_used = 2097 crash> list -s btree -l btree.list -H ffffa03fde4c1140|grep -E -A2 "^ lock = {" > btree_cache.txt crash> list -s btree -l btree.list -H ffffa03fde4c1150|grep -E -A2 "^ lock = {" > btree_cache_freeable.txt [root@node-3 127.0.0.1-2023-08-04-16:40:28]# pwd /var/crash/127.0.0.1-2023-08-04-16:40:28 [root@node-3 127.0.0.1-2023-08-04-16:40:28]# cat btree_cache.txt|grep counter|grep -v "counter = 0" [root@node-3 127.0.0.1-2023-08-04-16:40:28]# cat btree_cache_freeable.txt|grep counter|grep -v "counter = 0" counter = 1 We found that this is a bug in bch_sectors_dirty_init() when locking c->root: (1). Thread X has locked c->root(A) write. (2). Thread Y failed to lock c->root(A), waiting for the lock(c->root A). (3). Thread X bch_btree_set_root() changes c->root from A to B. (4). Thread X releases the lock(c->root A). (5). Thread Y successfully locks c->root(A). (6). Thread Y releases the lock(c->root B). down_write locked ---(1)----------------------┐ | | | down_read waiting ---(2)----┐ | | | ┌-------------┐ ┌-------------┐ bch_btree_set_root ===(3)========>> | c->root A | | c->root B | | | └-------------┘ └-------------┘ up_write ---(4)---------------------┘ | | | | | down_read locked ---(5)-----------┘ | | | up_read ---(6)-----------------------------┘ Since c->root may change, the correct steps to lock c->root should be the same as bch_root_usage(), compare after locking. static unsigned int bch_root_usage(struct cache_set *c) { unsigned int bytes = 0; struct bkey *k; struct btree *b; struct btree_iter iter; goto lock_root; do { rw_unlock(false, b); lock_root: b = c->root; rw_lock(false, b, b->level); } while (b != c->root); for_each_key_filter(&b->keys, k, &iter, bch_ptr_bad) bytes += bkey_bytes(k); rw_unlock(false, b); return (bytes * 100) / btree_bytes(c); } Fixes: b144e45fc576 ("bcache: make bch_sectors_dirty_init() to be multithreaded") Signed-off-by: Mingzhe Zou Cc: Signed-off-by: Coly Li Link: https://lore.kernel.org/r/20231120052503.6122-7-colyli@suse.de Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman

bcache: fixup init dirty data errors

2023-12-03T06:33:09+00:00

commit 7cc47e64d3d69786a2711a4767e26b26ba63d7ed upstream. We found that after long run, the dirty_data of the bcache device will have errors. This error cannot be eliminated unless re-register. We also found that reattach after detach, this error can accumulate. In bch_sectors_dirty_init(), all inode <= d->id keys will be recounted again. This is wrong, we only need to count the keys of the current device. Fixes: b144e45fc576 ("bcache: make bch_sectors_dirty_init() to be multithreaded") Signed-off-by: Mingzhe Zou Cc: Signed-off-by: Coly Li Link: https://lore.kernel.org/r/20231120052503.6122-6-colyli@suse.de Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman

bcache: fixup multi-threaded bch_sectors_dirty_init() wake-up race

2023-12-03T06:33:07+00:00

commit 2faac25d7958c4761bb8cec54adb79f806783ad6 upstream. We get a kernel crash about "unable to handle kernel paging request": ```dmesg [368033.032005] BUG: unable to handle kernel paging request at ffffffffad9ae4b5 [368033.032007] PGD fc3a0d067 P4D fc3a0d067 PUD fc3a0e063 PMD 8000000fc38000e1 [368033.032012] Oops: 0003 [#1] SMP PTI [368033.032015] CPU: 23 PID: 55090 Comm: bch_dirtcnt[0] Kdump: loaded Tainted: G OE --------- - - 4.18.0-147.5.1.es8_24.x86_64 #1 [368033.032017] Hardware name: Tsinghua Tongfang THTF Chaoqiang Server/072T6D, BIOS 2.4.3 01/17/2017 [368033.032027] RIP: 0010:native_queued_spin_lock_slowpath+0x183/0x1d0 [368033.032029] Code: 8b 02 48 85 c0 74 f6 48 89 c1 eb d0 c1 e9 12 83 e0 03 83 e9 01 48 c1 e0 05 48 63 c9 48 05 c0 3d 02 00 48 03 04 cd 60 68 93 ad <48> 89 10 8b 42 08 85 c0 75 09 f3 90 8b 42 08 85 c0 74 f7 48 8b 02 [368033.032031] RSP: 0018:ffffbb48852abe00 EFLAGS: 00010082 [368033.032032] RAX: ffffffffad9ae4b5 RBX: 0000000000000246 RCX: 0000000000003bf3 [368033.032033] RDX: ffff97b0ff8e3dc0 RSI: 0000000000600000 RDI: ffffbb4884743c68 [368033.032034] RBP: 0000000000000001 R08: 0000000000000000 R09: 000007ffffffffff [368033.032035] R10: ffffbb486bb01000 R11: 0000000000000001 R12: ffffffffc068da70 [368033.032036] R13: 0000000000000003 R14: 0000000000000000 R15: 0000000000000000 [368033.032038] FS: 0000000000000000(0000) GS:ffff97b0ff8c0000(0000) knlGS:0000000000000000 [368033.032039] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [368033.032040] CR2: ffffffffad9ae4b5 CR3: 0000000fc3a0a002 CR4: 00000000003626e0 [368033.032042] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [368033.032043] bcache: bch_cached_dev_attach() Caching rbd479 as bcache462 on set 8cff3c36-4a76-4242-afaa-7630206bc70b [368033.032045] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [368033.032046] Call Trace: [368033.032054] _raw_spin_lock_irqsave+0x32/0x40 [368033.032061] __wake_up_common_lock+0x63/0xc0 [368033.032073] ? bch_ptr_invalid+0x10/0x10 [bcache] [368033.033502] bch_dirty_init_thread+0x14c/0x160 [bcache] [368033.033511] ? read_dirty_submit+0x60/0x60 [bcache] [368033.033516] kthread+0x112/0x130 [368033.033520] ? kthread_flush_work_fn+0x10/0x10 [368033.034505] ret_from_fork+0x35/0x40 ``` The crash occurred when call wake_up(&state->wait), and then we want to look at the value in the state. However, bch_sectors_dirty_init() is not found in the stack of any task. Since state is allocated on the stack, we guess that bch_sectors_dirty_init() has exited, causing bch_dirty_init_thread() to be unable to handle kernel paging request. In order to verify this idea, we added some printing information during wake_up(&state->wait). We find that "wake up" is printed twice, however we only expect the last thread to wake up once. ```dmesg [ 994.641004] alcache: bch_dirty_init_thread() wake up [ 994.641018] alcache: bch_dirty_init_thread() wake up [ 994.641523] alcache: bch_sectors_dirty_init() init exit ``` There is a race. If bch_sectors_dirty_init() exits after the first wake up, the second wake up will trigger this bug("unable to handle kernel paging request"). Proceed as follows: bch_sectors_dirty_init kthread_run ==============> bch_dirty_init_thread(bch_dirtcnt[0]) ... ... atomic_inc(&state.started) ... ... ... atomic_read(&state.enough) ... ... atomic_set(&state->enough, 1) kthread_run ======================================================> bch_dirty_init_thread(bch_dirtcnt[1]) ... atomic_dec_and_test(&state->started) ... atomic_inc(&state.started) ... ... ... wake_up(&state->wait) ... atomic_read(&state.enough) atomic_dec_and_test(&state->started) ... ... wait_event(state.wait, atomic_read(&state.started) == 0) ... return ... wake_up(&state->wait) We believe it is very common to wake up twice if there is no dirty, but crash is an extremely low probability event. It's hard for us to reproduce this issue. We attached and detached continuously for a week, with a total of more than one million attaches and only one crash. Putting atomic_inc(&state.started) before kthread_run() can avoid waking up twice. Fixes: b144e45fc576 ("bcache: make bch_sectors_dirty_init() to be multithreaded") Signed-off-by: Mingzhe Zou Cc: Signed-off-by: Coly Li Link: https://lore.kernel.org/r/20231120052503.6122-8-colyli@suse.de Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman

bcache: fixup btree_cache_wait list damage

2023-06-15T13:32:55+00:00

We get a kernel crash about "list_add corruption. next->prev should be prev (ffff9c801bc01210), but was ffff9c77b688237c. (next=ffffae586d8afe68)." crash> struct list_head 0xffff9c801bc01210 struct list_head { next = 0xffffae586d8afe68, prev = 0xffffae586d8afe68 } crash> struct list_head 0xffff9c77b688237c struct list_head { next = 0x0, prev = 0x0 } crash> struct list_head 0xffffae586d8afe68 struct list_head struct: invalid kernel virtual address: ffffae586d8afe68 type: "gdb_readmem_callback" Cannot access memory at address 0xffffae586d8afe68 [230469.019492] Call Trace: [230469.032041] prepare_to_wait+0x8a/0xb0 [230469.044363] ? bch_btree_keys_free+0x6c/0xc0 [escache] [230469.056533] mca_cannibalize_lock+0x72/0x90 [escache] [230469.068788] mca_alloc+0x2ae/0x450 [escache] [230469.080790] bch_btree_node_get+0x136/0x2d0 [escache] [230469.092681] bch_btree_check_thread+0x1e1/0x260 [escache] [230469.104382] ? finish_wait+0x80/0x80 [230469.115884] ? bch_btree_check_recurse+0x1a0/0x1a0 [escache] [230469.127259] kthread+0x112/0x130 [230469.138448] ? kthread_flush_work_fn+0x10/0x10 [230469.149477] ret_from_fork+0x35/0x40 bch_btree_check_thread() and bch_dirty_init_thread() may call mca_cannibalize() to cannibalize other cached btree nodes. Only one thread can do it at a time, so the op of other threads will be added to the btree_cache_wait list. We must call finish_wait() to remove op from btree_cache_wait before free it's memory address. Otherwise, the list will be damaged. Also should call bch_cannibalize_unlock() to release the btree_cache_alloc_lock and wake_up other waiters. Fixes: 8e7102273f59 ("bcache: make bch_btree_check() to be multithreaded") Fixes: b144e45fc576 ("bcache: make bch_sectors_dirty_init() to be multithreaded") Cc: stable@vger.kernel.org Signed-off-by: Mingzhe Zou Signed-off-by: Coly Li Link: https://lore.kernel.org/r/20230615121223.22502-7-colyli@suse.de Signed-off-by: Jens Axboe

block: remove bio_set_op_attrs

2022-12-07T16:43:12+00:00

This macro is obsolete, so replace the last few uses with open coded bi_opf assignments. Signed-off-by: Christoph Hellwig Acked-by: Coly Li > Reviewed-by: Johannes Thumshirn Reviewed-by: Bart Van Assche Link: https://lore.kernel.org/r/20221206144057.720846-1-hch@lst.de Signed-off-by: Jens Axboe

bcache: fix set_at_max_writeback_rate() for multiple attached devices

2022-09-19T17:12:35+00:00

Inside set_at_max_writeback_rate() the calculation in following if() check is wrong, if (atomic_inc_return(&c->idle_counter) < atomic_read(&c->attached_dev_nr) * 6) Because each attached backing device has its own writeback thread running and increasing c->idle_counter, the counter increates much faster than expected. The correct calculation should be, (counter / dev_nr) < dev_nr * 6 which equals to, counter < dev_nr * dev_nr * 6 This patch fixes the above mistake with correct calculation, and helper routine idle_counter_exceeded() is added to make code be more clear. Reported-by: Mingzhe Zou Signed-off-by: Coly Li Acked-by: Mingzhe Zou Link: https://lore.kernel.org/r/20220919161647.81238-6-colyli@suse.de Signed-off-by: Jens Axboe

bcache: remove unnecessary flush_workqueue

2022-09-19T17:12:35+00:00

All pending works will be drained by destroy_workqueue(), no need to call flush_workqueue() explicitly. Signed-off-by: Li Lei Signed-off-by: Coly Li Link: https://lore.kernel.org/r/20220919161647.81238-2-colyli@suse.de Signed-off-by: Jens Axboe

bcache: avoid unnecessary soft lockup in kworker update_writeback_rate()

2022-05-28T12:48:26+00:00

The kworker routine update_writeback_rate() is schedued to update the writeback rate in every 5 seconds by default. Before calling __update_writeback_rate() to do real job, semaphore dc->writeback_lock should be held by the kworker routine. At the same time, bcache writeback thread routine bch_writeback_thread() also needs to hold dc->writeback_lock before flushing dirty data back into the backing device. If the dirty data set is large, it might be very long time for bch_writeback_thread() to scan all dirty buckets and releases dc->writeback_lock. In such case update_writeback_rate() can be starved for long enough time so that kernel reports a soft lockup warn- ing started like: watchdog: BUG: soft lockup - CPU#246 stuck for 23s! [kworker/246:31:179713] Such soft lockup condition is unnecessary, because after the writeback thread finishes its job and releases dc->writeback_lock, the kworker update_writeback_rate() may continue to work and everything is fine indeed. This patch avoids the unnecessary soft lockup by the following method, - Add new member to struct cached_dev - dc->rate_update_retry (0 by default) - In update_writeback_rate() call down_read_trylock(&dc->writeback_lock) firstly, if it fails then lock contention happens. - If dc->rate_update_retry <= BCH_WBRATE_UPDATE_MAX_SKIPS (15), doesn't acquire the lock and reschedules the kworker for next try. - If dc->rate_update_retry > BCH_WBRATE_UPDATE_MAX_SKIPS, no retry anymore and call down_read(&dc->writeback_lock) to wait for the lock. By the above method, at worst case update_writeback_rate() may retry for 1+ minutes before blocking on dc->writeback_lock by calling down_read(). For a 4TB cache device with 1TB dirty data, 90%+ of the unnecessary soft lockup warning message can be avoided. When retrying to acquire dc->writeback_lock in update_writeback_rate(), of course the writeback rate cannot be updated. It is fair, because when the kworker is blocked on the lock contention of dc->writeback_lock, the writeback rate cannot be updated neither. This change follows Jens Axboe's suggestion to a more clear and simple version. Signed-off-by: Coly Li Link: https://lore.kernel.org/r/20220528124550.32834-2-colyli@suse.de Signed-off-by: Jens Axboe