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From: Kent Overstreet To: Alan Huang Cc: linux-bcachefs@vger.kernel.org, syzbot+fe63f377148a6371a9db@syzkaller.appspotmail.com, linux-mm@kvack.org, Tejun Heo , Dennis Zhou , Christoph Lameter Subject: Re: [PATCH] bcachefs: Use alloc_percpu_gfp to avoid deadlock Message-ID: References: <20250212100625.55860-1-mmpgouride@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250212100625.55860-1-mmpgouride@gmail.com> X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Queue-Id: 8D6D280016 X-Rspamd-Server: rspam12 X-Stat-Signature: x46b1d5an8934ytfxpt7gwraso6ifpzr X-HE-Tag: 1739370461-255079 X-HE-Meta: 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 wWxFdsKq iHeYhBmj1jt/Aw/qJNB+P22KmKBJx1duiKWTYqiMLecViSKrW8hKGhnaJ3vljgjW0PyQcGr3EI9H3II6lvFkXQ3WdDaz0p81aauXUg3uZLht0tZja3SAQvBCzG7LRrT09BimcMBV2lqx2AdoG4hGILUzGU9COVkjEu0pQml4nyD7BecQCpBxV0spuLZAmDiBGWAXoqX3lXok1zoZkOikpe/BI+KZJO7KWMIGkBqwx5HDFam+iNbXBW7mHw3inwmNMEGIDRTxZZzC+vHz+RzPc7MvuVPfLSupNSG0xu0jckuKyk8QuMFdspO/XgEqolCf8WtDS5unB+IFtNe28BQ80OOeFmCBzYLO6kZm2b/uPGmWMggdMNY7F2Kfg3HiSUXE3Wq27oLj+1eDkwcA/XlBG9H/d8A== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000004, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Adding pcpu people to the CC On Wed, Feb 12, 2025 at 06:06:25PM +0800, Alan Huang wrote: > The cycle: > > CPU0: CPU1: > bc->lock pcpu_alloc_mutex > pcpu_alloc_mutex bc->lock > > Reported-by: syzbot+fe63f377148a6371a9db@syzkaller.appspotmail.com > Tested-by: syzbot+fe63f377148a6371a9db@syzkaller.appspotmail.com > Signed-off-by: Alan Huang So pcpu_alloc_mutex -> fs_reclaim? That's really awkward; seems like something that might invite more issues. We can apply your fix if we need to, but I want to hear with the percpu people have to say first. ====================================================== WARNING: possible circular locking dependency detected 6.14.0-rc2-syzkaller-00039-g09fbf3d50205 #0 Not tainted ------------------------------------------------------ syz.0.21/5625 is trying to acquire lock: ffffffff8ea19608 (pcpu_alloc_mutex){+.+.}-{4:4}, at: pcpu_alloc_noprof+0x293/0x1760 mm/percpu.c:1782 but task is already holding lock: ffff888051401c68 (&bc->lock){+.+.}-{4:4}, at: bch2_btree_node_mem_alloc+0x559/0x16f0 fs/bcachefs/btree_cache.c:804 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (&bc->lock){+.+.}-{4:4}: lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5851 __mutex_lock_common kernel/locking/mutex.c:585 [inline] __mutex_lock+0x19c/0x1010 kernel/locking/mutex.c:730 bch2_btree_cache_scan+0x184/0xec0 fs/bcachefs/btree_cache.c:482 do_shrink_slab+0x72d/0x1160 mm/shrinker.c:437 shrink_slab+0x1093/0x14d0 mm/shrinker.c:664 shrink_one+0x43b/0x850 mm/vmscan.c:4868 shrink_many mm/vmscan.c:4929 [inline] lru_gen_shrink_node mm/vmscan.c:5007 [inline] shrink_node+0x37c5/0x3e50 mm/vmscan.c:5978 kswapd_shrink_node mm/vmscan.c:6807 [inline] balance_pgdat mm/vmscan.c:6999 [inline] kswapd+0x20f3/0x3b10 mm/vmscan.c:7264 kthread+0x7a9/0x920 kernel/kthread.c:464 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:148 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244 -> #1 (fs_reclaim){+.+.}-{0:0}: lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5851 __fs_reclaim_acquire mm/page_alloc.c:3853 [inline] fs_reclaim_acquire+0x88/0x130 mm/page_alloc.c:3867 might_alloc include/linux/sched/mm.h:318 [inline] slab_pre_alloc_hook mm/slub.c:4066 [inline] slab_alloc_node mm/slub.c:4144 [inline] __do_kmalloc_node mm/slub.c:4293 [inline] __kmalloc_noprof+0xae/0x4c0 mm/slub.c:4306 kmalloc_noprof include/linux/slab.h:905 [inline] kzalloc_noprof include/linux/slab.h:1037 [inline] pcpu_mem_zalloc mm/percpu.c:510 [inline] pcpu_alloc_chunk mm/percpu.c:1430 [inline] pcpu_create_chunk+0x57/0xbc0 mm/percpu-vm.c:338 pcpu_balance_populated mm/percpu.c:2063 [inline] pcpu_balance_workfn+0xc4d/0xd40 mm/percpu.c:2200 process_one_work kernel/workqueue.c:3236 [inline] process_scheduled_works+0xa66/0x1840 kernel/workqueue.c:3317 worker_thread+0x870/0xd30 kernel/workqueue.c:3398 kthread+0x7a9/0x920 kernel/kthread.c:464 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:148 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244 -> #0 (pcpu_alloc_mutex){+.+.}-{4:4}: check_prev_add kernel/locking/lockdep.c:3163 [inline] check_prevs_add kernel/locking/lockdep.c:3282 [inline] validate_chain+0x18ef/0x5920 kernel/locking/lockdep.c:3906 __lock_acquire+0x1397/0x2100 kernel/locking/lockdep.c:5228 lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5851 __mutex_lock_common kernel/locking/mutex.c:585 [inline] __mutex_lock+0x19c/0x1010 kernel/locking/mutex.c:730 pcpu_alloc_noprof+0x293/0x1760 mm/percpu.c:1782 __six_lock_init+0x104/0x150 fs/bcachefs/six.c:876 bch2_btree_lock_init+0x38/0x100 fs/bcachefs/btree_locking.c:12 bch2_btree_node_mem_alloc+0x565/0x16f0 fs/bcachefs/btree_cache.c:807 __bch2_btree_node_alloc fs/bcachefs/btree_update_interior.c:304 [inline] bch2_btree_reserve_get+0x2df/0x1890 fs/bcachefs/btree_update_interior.c:532 bch2_btree_update_start+0xe56/0x14e0 fs/bcachefs/btree_update_interior.c:1230 bch2_btree_split_leaf+0x121/0x880 fs/bcachefs/btree_update_interior.c:1851 bch2_trans_commit_error+0x212/0x1380 fs/bcachefs/btree_trans_commit.c:908 __bch2_trans_commit+0x812b/0x97a0 fs/bcachefs/btree_trans_commit.c:1085 bch2_trans_commit fs/bcachefs/btree_update.h:183 [inline] bch2_trans_mark_metadata_bucket+0x47a/0x17b0 fs/bcachefs/buckets.c:1043 bch2_trans_mark_metadata_sectors fs/bcachefs/buckets.c:1060 [inline] __bch2_trans_mark_dev_sb fs/bcachefs/buckets.c:1100 [inline] bch2_trans_mark_dev_sb+0x3f6/0x820 fs/bcachefs/buckets.c:1128 bch2_trans_mark_dev_sbs_flags+0x6be/0x720 fs/bcachefs/buckets.c:1138 bch2_fs_initialize+0xba0/0x1610 fs/bcachefs/recovery.c:1149 bch2_fs_start+0x36d/0x610 fs/bcachefs/super.c:1042 bch2_fs_get_tree+0xd8d/0x1740 fs/bcachefs/fs.c:2203 vfs_get_tree+0x90/0x2b0 fs/super.c:1814 do_new_mount+0x2be/0xb40 fs/namespace.c:3560 do_mount fs/namespace.c:3900 [inline] __do_sys_mount fs/namespace.c:4111 [inline] __se_sys_mount+0x2d6/0x3c0 fs/namespace.c:4088 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f other info that might help us debug this: Chain exists of: pcpu_alloc_mutex --> fs_reclaim --> &bc->lock Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&bc->lock); lock(fs_reclaim); lock(&bc->lock); lock(pcpu_alloc_mutex); *** DEADLOCK *** 4 locks held by syz.0.21/5625: #0: ffff888051400278 (&c->state_lock){+.+.}-{4:4}, at: bch2_fs_start+0x45/0x610 fs/bcachefs/super.c:1010 #1: ffff888051404378 (&c->btree_trans_barrier){.+.+}-{0:0}, at: srcu_lock_acquire include/linux/srcu.h:164 [inline] #1: ffff888051404378 (&c->btree_trans_barrier){.+.+}-{0:0}, at: srcu_read_lock include/linux/srcu.h:256 [inline] #1: ffff888051404378 (&c->btree_trans_barrier){.+.+}-{0:0}, at: __bch2_trans_get+0x7e4/0xd30 fs/bcachefs/btree_iter.c:3377 #2: ffff8880514266d0 (&c->gc_lock){.+.+}-{4:4}, at: bch2_btree_update_start+0x682/0x14e0 fs/bcachefs/btree_update_interior.c:1180 #3: ffff888051401c68 (&bc->lock){+.+.}-{4:4}, at: bch2_btree_node_mem_alloc+0x559/0x16f0 fs/bcachefs/btree_cache.c:804 stack backtrace: CPU: 0 UID: 0 PID: 5625 Comm: syz.0.21 Not tainted 6.14.0-rc2-syzkaller-00039-g09fbf3d50205 #0 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014 Call Trace: __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120 print_circular_bug+0x13a/0x1b0 kernel/locking/lockdep.c:2076 check_noncircular+0x36a/0x4a0 kernel/locking/lockdep.c:2208 check_prev_add kernel/locking/lockdep.c:3163 [inline] check_prevs_add kernel/locking/lockdep.c:3282 [inline] validate_chain+0x18ef/0x5920 kernel/locking/lockdep.c:3906 __lock_acquire+0x1397/0x2100 kernel/locking/lockdep.c:5228 lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5851 __mutex_lock_common kernel/locking/mutex.c:585 [inline] __mutex_lock+0x19c/0x1010 kernel/locking/mutex.c:730 pcpu_alloc_noprof+0x293/0x1760 mm/percpu.c:1782 __six_lock_init+0x104/0x150 fs/bcachefs/six.c:876 bch2_btree_lock_init+0x38/0x100 fs/bcachefs/btree_locking.c:12 bch2_btree_node_mem_alloc+0x565/0x16f0 fs/bcachefs/btree_cache.c:807 __bch2_btree_node_alloc fs/bcachefs/btree_update_interior.c:304 [inline] bch2_btree_reserve_get+0x2df/0x1890 fs/bcachefs/btree_update_interior.c:532 bch2_btree_update_start+0xe56/0x14e0 fs/bcachefs/btree_update_interior.c:1230 bch2_btree_split_leaf+0x121/0x880 fs/bcachefs/btree_update_interior.c:1851 bch2_trans_commit_error+0x212/0x1380 fs/bcachefs/btree_trans_commit.c:908 __bch2_trans_commit+0x812b/0x97a0 fs/bcachefs/btree_trans_commit.c:1085 bch2_trans_commit fs/bcachefs/btree_update.h:183 [inline] bch2_trans_mark_metadata_bucket+0x47a/0x17b0 fs/bcachefs/buckets.c:1043 bch2_trans_mark_metadata_sectors fs/bcachefs/buckets.c:1060 [inline] __bch2_trans_mark_dev_sb fs/bcachefs/buckets.c:1100 [inline] bch2_trans_mark_dev_sb+0x3f6/0x820 fs/bcachefs/buckets.c:1128 bch2_trans_mark_dev_sbs_flags+0x6be/0x720 fs/bcachefs/buckets.c:1138 bch2_fs_initialize+0xba0/0x1610 fs/bcachefs/recovery.c:1149 bch2_fs_start+0x36d/0x610 fs/bcachefs/super.c:1042 bch2_fs_get_tree+0xd8d/0x1740 fs/bcachefs/fs.c:2203 vfs_get_tree+0x90/0x2b0 fs/super.c:1814 do_new_mount+0x2be/0xb40 fs/namespace.c:3560 do_mount fs/namespace.c:3900 [inline] __do_sys_mount fs/namespace.c:4111 [inline] __se_sys_mount+0x2d6/0x3c0 fs/namespace.c:4088 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7fcaed38e58a Code: d8 64 89 02 48 c7 c0 ff ff ff ff eb a6 e8 de 1a 00 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007fcaec5fde68 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5 RAX: ffffffffffffffda RBX: 00007fcaec5fdef0 RCX: 00007fcaed38e58a RDX: 00004000000000c0 RSI: 0000400000000180 RDI: 00007fcaec5fdeb0 RBP: 00004000000000c0 R08: 00007fcaec5fdef0 R09: 0000000000000000 > --- > fs/bcachefs/six.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/bcachefs/six.c b/fs/bcachefs/six.c > index 7e7c66a1e1a6..ccdc6d496910 100644 > --- a/fs/bcachefs/six.c > +++ b/fs/bcachefs/six.c > @@ -873,7 +873,7 @@ void __six_lock_init(struct six_lock *lock, const char *name, > * failure if they wish by checking lock->readers, but generally > * will not want to treat it as an error. > */ > - lock->readers = alloc_percpu(unsigned); > + lock->readers = alloc_percpu_gfp(unsigned, GFP_NOWAIT|__GFP_NOWARN); > } > #endif > } > -- > 2.47.0 >