* [PATCH] bcachefs: Use alloc_percpu_gfp to avoid deadlock @ 2025-02-12 10:06 Alan Huang 2025-02-12 14:27 ` Kent Overstreet 0 siblings, 1 reply; 10+ messages in thread From: Alan Huang @ 2025-02-12 10:06 UTC (permalink / raw) To: kent.overstreet; +Cc: linux-bcachefs, Alan Huang, syzbot+fe63f377148a6371a9db 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 <mmpgouride@gmail.com> --- 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 ^ permalink raw reply related [flat|nested] 10+ messages in thread
* Re: [PATCH] bcachefs: Use alloc_percpu_gfp to avoid deadlock 2025-02-12 10:06 [PATCH] bcachefs: Use alloc_percpu_gfp to avoid deadlock Alan Huang @ 2025-02-12 14:27 ` Kent Overstreet 2025-02-20 10:57 ` Alan Huang 0 siblings, 1 reply; 10+ messages in thread From: Kent Overstreet @ 2025-02-12 14:27 UTC (permalink / raw) To: Alan Huang Cc: linux-bcachefs, syzbot+fe63f377148a6371a9db, linux-mm, Tejun Heo, Dennis Zhou, Christoph Lameter 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 <mmpgouride@gmail.com> 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: <TASK> __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 > ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH] bcachefs: Use alloc_percpu_gfp to avoid deadlock 2025-02-12 14:27 ` Kent Overstreet @ 2025-02-20 10:57 ` Alan Huang 2025-02-20 12:40 ` Kent Overstreet 2025-02-20 17:16 ` Vlastimil Babka 0 siblings, 2 replies; 10+ messages in thread From: Alan Huang @ 2025-02-20 10:57 UTC (permalink / raw) To: Kent Overstreet Cc: linux-bcachefs, syzbot+fe63f377148a6371a9db, linux-mm, Tejun Heo, Dennis Zhou, Christoph Lameter Ping > On Feb 12, 2025, at 22:27, Kent Overstreet <kent.overstreet@linux.dev> wrote: > > 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 <mmpgouride@gmail.com> > > 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: > <TASK> > __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 >> ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH] bcachefs: Use alloc_percpu_gfp to avoid deadlock 2025-02-20 10:57 ` Alan Huang @ 2025-02-20 12:40 ` Kent Overstreet 2025-02-20 12:44 ` Alan Huang 2025-02-20 17:16 ` Vlastimil Babka 1 sibling, 1 reply; 10+ messages in thread From: Kent Overstreet @ 2025-02-20 12:40 UTC (permalink / raw) To: Alan Huang Cc: linux-bcachefs, syzbot+fe63f377148a6371a9db, linux-mm, Tejun Heo, Dennis Zhou, Christoph Lameter On Thu, Feb 20, 2025 at 06:57:32PM +0800, Alan Huang wrote: > Ping I really want to get this fixed in percpu... let's leave this until we can fix it properly, this has come up before and I don't want to just kick the can down again (yes, that means fixing the global percpu allocation lock) > > > On Feb 12, 2025, at 22:27, Kent Overstreet <kent.overstreet@linux.dev> wrote: > > > > 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 <mmpgouride@gmail.com> > > > > 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: > > <TASK> > > __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 > >> > ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH] bcachefs: Use alloc_percpu_gfp to avoid deadlock 2025-02-20 12:40 ` Kent Overstreet @ 2025-02-20 12:44 ` Alan Huang 0 siblings, 0 replies; 10+ messages in thread From: Alan Huang @ 2025-02-20 12:44 UTC (permalink / raw) To: Kent Overstreet Cc: linux-bcachefs, syzbot+fe63f377148a6371a9db, linux-mm, Tejun Heo, Dennis Zhou, Christoph Lameter > On Feb 20, 2025, at 20:40, Kent Overstreet <kent.overstreet@linux.dev> wrote: > > On Thu, Feb 20, 2025 at 06:57:32PM +0800, Alan Huang wrote: >> Ping > > I really want to get this fixed in percpu... > > let's leave this until we can fix it properly, this has come up before > and I don't want to just kick the can down again > > (yes, that means fixing the global percpu allocation lock) The ping is for the percpu people... > >> >>> On Feb 12, 2025, at 22:27, Kent Overstreet <kent.overstreet@linux.dev> wrote: >>> >>> 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 <mmpgouride@gmail.com> >>> >>> 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: >>> <TASK> >>> __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 >>>> >> ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH] bcachefs: Use alloc_percpu_gfp to avoid deadlock 2025-02-20 10:57 ` Alan Huang 2025-02-20 12:40 ` Kent Overstreet @ 2025-02-20 17:16 ` Vlastimil Babka 2025-02-20 20:37 ` Kent Overstreet 1 sibling, 1 reply; 10+ messages in thread From: Vlastimil Babka @ 2025-02-20 17:16 UTC (permalink / raw) To: Alan Huang, Kent Overstreet Cc: linux-bcachefs, syzbot+fe63f377148a6371a9db, linux-mm, Tejun Heo, Dennis Zhou, Christoph Lameter, Michal Hocko On 2/20/25 11:57, Alan Huang wrote: > Ping > >> On Feb 12, 2025, at 22:27, Kent Overstreet <kent.overstreet@linux.dev> wrote: >> >> 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 <mmpgouride@gmail.com> >> >> 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 Seeing this as part of the chain (fs reclaim from a worker doing pcpu_balance_workfn) makes me think Michal's patch could be a fix to this: https://lore.kernel.org/all/20250206122633.167896-1-mhocko@kernel.org/ >> -> #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: >> <TASK> >> __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 >>> > > ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH] bcachefs: Use alloc_percpu_gfp to avoid deadlock 2025-02-20 17:16 ` Vlastimil Babka @ 2025-02-20 20:37 ` Kent Overstreet 2025-02-21 2:46 ` Dennis Zhou 0 siblings, 1 reply; 10+ messages in thread From: Kent Overstreet @ 2025-02-20 20:37 UTC (permalink / raw) To: Vlastimil Babka Cc: Alan Huang, linux-bcachefs, syzbot+fe63f377148a6371a9db, linux-mm, Tejun Heo, Dennis Zhou, Christoph Lameter, Michal Hocko On Thu, Feb 20, 2025 at 06:16:43PM +0100, Vlastimil Babka wrote: > On 2/20/25 11:57, Alan Huang wrote: > > Ping > > > >> On Feb 12, 2025, at 22:27, Kent Overstreet <kent.overstreet@linux.dev> wrote: > >> > >> 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 <mmpgouride@gmail.com> > >> > >> 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 > > Seeing this as part of the chain (fs reclaim from a worker doing > pcpu_balance_workfn) makes me think Michal's patch could be a fix to this: > > https://lore.kernel.org/all/20250206122633.167896-1-mhocko@kernel.org/ Thanks for the link - that does look like just the thing. ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH] bcachefs: Use alloc_percpu_gfp to avoid deadlock 2025-02-20 20:37 ` Kent Overstreet @ 2025-02-21 2:46 ` Dennis Zhou 2025-02-21 7:21 ` Vlastimil Babka 2025-02-21 19:44 ` Alan Huang 0 siblings, 2 replies; 10+ messages in thread From: Dennis Zhou @ 2025-02-21 2:46 UTC (permalink / raw) To: Kent Overstreet Cc: Vlastimil Babka, Alan Huang, linux-bcachefs, syzbot+fe63f377148a6371a9db, linux-mm, Tejun Heo, Christoph Lameter, Michal Hocko Hello, On Thu, Feb 20, 2025 at 03:37:26PM -0500, Kent Overstreet wrote: > On Thu, Feb 20, 2025 at 06:16:43PM +0100, Vlastimil Babka wrote: > > On 2/20/25 11:57, Alan Huang wrote: > > > Ping > > > > > >> On Feb 12, 2025, at 22:27, Kent Overstreet <kent.overstreet@linux.dev> wrote: > > >> > > >> 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 <mmpgouride@gmail.com> > > >> > > >> 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 > > > > Seeing this as part of the chain (fs reclaim from a worker doing > > pcpu_balance_workfn) makes me think Michal's patch could be a fix to this: > > > > https://lore.kernel.org/all/20250206122633.167896-1-mhocko@kernel.org/ > > Thanks for the link - that does look like just the thing. Sorry I missed the first email asking to weigh in. Michal's problem is a little bit different than what's happening here. He's having an issue where a alloc_percpu_gfp(NOFS/NOIO) is considered atomic and failing during probing. This is because we don't have enough percpu memory backed to fulfill the "atomic" requests. Historically we've considered any allocation that's not GFP_KERNEL to be atomic. Here it seems like the alloc_percpu() behind the bc->lock() should have been an "atomic" allocation to prevent the lock cycle? Thanks, Dennis ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH] bcachefs: Use alloc_percpu_gfp to avoid deadlock 2025-02-21 2:46 ` Dennis Zhou @ 2025-02-21 7:21 ` Vlastimil Babka 2025-02-21 19:44 ` Alan Huang 1 sibling, 0 replies; 10+ messages in thread From: Vlastimil Babka @ 2025-02-21 7:21 UTC (permalink / raw) To: Dennis Zhou, Kent Overstreet Cc: Alan Huang, linux-bcachefs, syzbot+fe63f377148a6371a9db, linux-mm, Tejun Heo, Christoph Lameter, Michal Hocko On 2/21/25 03:46, Dennis Zhou wrote: > Hello, > > On Thu, Feb 20, 2025 at 03:37:26PM -0500, Kent Overstreet wrote: >> On Thu, Feb 20, 2025 at 06:16:43PM +0100, Vlastimil Babka wrote: >> > On 2/20/25 11:57, Alan Huang wrote: >> > > Ping >> > > >> > >> On Feb 12, 2025, at 22:27, Kent Overstreet <kent.overstreet@linux.dev> wrote: >> > >> >> > >> 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 <mmpgouride@gmail.com> >> > >> >> > >> 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 >> > >> > Seeing this as part of the chain (fs reclaim from a worker doing >> > pcpu_balance_workfn) makes me think Michal's patch could be a fix to this: >> > >> > https://lore.kernel.org/all/20250206122633.167896-1-mhocko@kernel.org/ >> >> Thanks for the link - that does look like just the thing. > > Sorry I missed the first email asking to weigh in. > > Michal's problem is a little bit different than what's happening here. Yes, but it's related enough. He mentions commit 28307d938fb2 and there you find a similar kind of lockdep splat. > He's having an issue where a alloc_percpu_gfp(NOFS/NOIO) is considered > atomic and failing during probing. This is because we don't have enough > percpu memory backed to fulfill the "atomic" requests. That, and we don't allow NOFS/NOIO to take the pcpu_alloc_mutex to avoid deadlock with pcpu_balance_workfn taking it and then doing __GFP_FS reclaim. > Historically we've considered any allocation that's not GFP_KERNEL to be > atomic. Here it seems like the alloc_percpu() behind the bc->lock() > should have been an "atomic" allocation to prevent the lock cycle? That's what the original mail/patch in this thread suggested: https://lore.kernel.org/all/20250212100625.55860-1-mmpgouride@gmail.com/ Note it proposes GFP_NOWAIT, possibly GFP_NOFS would be enough, but then the current implementation could would make it "atomic" anyway. But then it could end up failing like the allocations that motivated Michal's patch? So with Michal's approach we can avoid having to weaken pcpu_alloc() callers like this. Yes it's counter-intuitive that we weaken a kworker context instead, which normally has no restrictions. But it's not weakened (NOIO) nearly as much as pcpu_alloc() users that are effectively atomic when they can't take pcpu_alloc mutex at all. > Thanks, > Dennis > ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH] bcachefs: Use alloc_percpu_gfp to avoid deadlock 2025-02-21 2:46 ` Dennis Zhou 2025-02-21 7:21 ` Vlastimil Babka @ 2025-02-21 19:44 ` Alan Huang 1 sibling, 0 replies; 10+ messages in thread From: Alan Huang @ 2025-02-21 19:44 UTC (permalink / raw) To: Dennis Zhou Cc: Kent Overstreet, Vlastimil Babka, linux-bcachefs, syzbot+fe63f377148a6371a9db, linux-mm, Tejun Heo, Christoph Lameter, Michal Hocko On Feb 21, 2025, at 10:46, Dennis Zhou <dennis@kernel.org> wrote: > > Hello, > > On Thu, Feb 20, 2025 at 03:37:26PM -0500, Kent Overstreet wrote: >> On Thu, Feb 20, 2025 at 06:16:43PM +0100, Vlastimil Babka wrote: >>> On 2/20/25 11:57, Alan Huang wrote: >>>> Ping >>>> >>>>> On Feb 12, 2025, at 22:27, Kent Overstreet <kent.overstreet@linux.dev> wrote: >>>>> >>>>> 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 <mmpgouride@gmail.com> >>>>> >>>>> 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 >>> >>> Seeing this as part of the chain (fs reclaim from a worker doing >>> pcpu_balance_workfn) makes me think Michal's patch could be a fix to this: >>> >>> https://lore.kernel.org/all/20250206122633.167896-1-mhocko@kernel.org/ >> >> Thanks for the link - that does look like just the thing. > > Sorry I missed the first email asking to weigh in. > > Michal's problem is a little bit different than what's happening here. > He's having an issue where a alloc_percpu_gfp(NOFS/NOIO) is considered > atomic and failing during probing. This is because we don't have enough > percpu memory backed to fulfill the "atomic" requests. > > Historically we've considered any allocation that's not GFP_KERNEL to be > atomic. Here it seems like the alloc_percpu() behind the bc->lock() > should have been an "atomic" allocation to prevent the lock cycle? I think so, if I understand it correctly, NOFS/NOIO could invoke the shrinker, so we can lock bc->lock again. And I think we should not rely on the implementation of alloc_percpu_gfp, but the GFP flags instead. Correct me if I'm wrong. > Thanks, > Dennis ^ permalink raw reply [flat|nested] 10+ messages in thread
end of thread, other threads:[~2025-02-21 19:44 UTC | newest] Thread overview: 10+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 2025-02-12 10:06 [PATCH] bcachefs: Use alloc_percpu_gfp to avoid deadlock Alan Huang 2025-02-12 14:27 ` Kent Overstreet 2025-02-20 10:57 ` Alan Huang 2025-02-20 12:40 ` Kent Overstreet 2025-02-20 12:44 ` Alan Huang 2025-02-20 17:16 ` Vlastimil Babka 2025-02-20 20:37 ` Kent Overstreet 2025-02-21 2:46 ` Dennis Zhou 2025-02-21 7:21 ` Vlastimil Babka 2025-02-21 19:44 ` Alan Huang
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