On Tue, Mar 26, 2024 at 12:53:35PM -0700, Alexei Starovoitov wrote: > Hi Paul, > > syzbot found an interesting false positive deadlock. > See below. > My understanding is the following: > > cpu 2: > grabs timer_base lock > spins on bpf_lpm lock > > cpu 1: > grab rcu krcp lock > spins on timer_base lock > > cpu 0: > grab bpf_lpm lock > spins on rcu krcp lock > > bpf_lpm lock can be the same. > timer_base lock can also be the same due to timer migration. > > but rcu krcp lock is always per-cpu, so it cannot be the same lock. > Hence it's a false positive, but still interesting. > > I don't think rcu can tell lockdep that these are different locks. It might be possible. I will play with this tomorrow, modeling after the use of lockdep_set_class_and_name() in rcu_init_one(). I am a bit concerned about systems with thousands of CPUs, but it just might be OK. > Few ideas/questions on how to address this: > > 1. in kernel/rcu/tree.c: > if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING) > schedule_delayed_monitor_work(krcp); > > unlock_return: > krc_this_cpu_unlock(krcp, flags); > > moving schedule_delayed_monitor_work() after unlock will not work, right? If telling lockdep that these are different locks works, that should be easier. Though maybe Uladzislau can assure me that moving this schedule_delayed_monitor_work() is OK. Thanx, Paul > 2. if not, we can move 4 kfree_rcu-s in kernel/bpf/lpm_trie.c > to a place after unlock of lpm_trie > > 3. move bpf_lpm_trie to bpf_mem_alloc. > > The 2 or 3 will address this false positive. > > Other ideas? > > On Tue, Mar 26, 2024 at 12:00 PM syzbot > <syzbot+1fa663a2100308ab6eab@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > > > Hello, > > > > syzbot found the following issue on: > > > > HEAD commit: fe46a7dd189e Merge tag 'sound-6.9-rc1' of git://git.kernel.. > > git tree: upstream > > console output: https://syzkaller.appspot.com/x/log.txt?x=11547a65180000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=4d90a36f0cab495a > > dashboard link: https://syzkaller.appspot.com/bug?extid=1fa663a2100308ab6eab > > compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40 > > > > Unfortunately, I don't have any reproducer for this issue yet. > > > > Downloadable assets: > > disk image: https://storage.googleapis.com/syzbot-assets/f6c04726a2ae/disk-fe46a7dd.raw.xz > > vmlinux: https://storage.googleapis.com/syzbot-assets/09c26ce901ea/vmlinux-fe46a7dd.xz > > kernel image: https://storage.googleapis.com/syzbot-assets/134acf7f5322/bzImage-fe46a7dd.xz > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > Reported-by: syzbot+1fa663a2100308ab6eab@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > ====================================================== > > WARNING: possible circular locking dependency detected > > 6.8.0-syzkaller-08951-gfe46a7dd189e #0 Not tainted > > ------------------------------------------------------ > > syz-executor.3/6590 is trying to acquire lock: > > ffff8880b9529470 (krc.lock){..-.}-{2:2}, at: krc_this_cpu_lock kernel/rcu/tree.c:2960 [inline] > > ffff8880b9529470 (krc.lock){..-.}-{2:2}, at: add_ptr_to_bulk_krc_lock kernel/rcu/tree.c:3359 [inline] > > ffff8880b9529470 (krc.lock){..-.}-{2:2}, at: kvfree_call_rcu+0x18a/0x790 kernel/rcu/tree.c:3444 > > > > but task is already holding lock: > > ffff888021a271f8 (&trie->lock){..-.}-{2:2}, at: trie_update_elem+0xcb/0xc10 kernel/bpf/lpm_trie.c:324 > > > > which lock already depends on the new lock. > > > > > > the existing dependency chain (in reverse order) is: > > > > -> #2 (&trie->lock){..-.}-{2:2}: > > lock_acquire+0x1e4/0x530 kernel/locking/lockdep.c:5754 > > __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline] > > _raw_spin_lock_irqsave+0xd5/0x120 kernel/locking/spinlock.c:162 > > trie_delete_elem+0x96/0x6a0 kernel/bpf/lpm_trie.c:451 > > bpf_prog_510c7248c5f60c92+0x2e/0x46 > > bpf_dispatcher_nop_func include/linux/bpf.h:1234 [inline] > > __bpf_prog_run include/linux/filter.h:657 [inline] > > bpf_prog_run include/linux/filter.h:664 [inline] > > __bpf_trace_run kernel/trace/bpf_trace.c:2381 [inline] > > bpf_trace_run2+0x204/0x420 kernel/trace/bpf_trace.c:2420 > > trace_timer_start include/trace/events/timer.h:52 [inline] > > enqueue_timer+0x396/0x550 kernel/time/timer.c:663 > > internal_add_timer kernel/time/timer.c:688 [inline] > > __mod_timer+0xa0e/0xeb0 kernel/time/timer.c:1183 > > call_timer_fn+0x17e/0x600 kernel/time/timer.c:1792 > > expire_timers kernel/time/timer.c:1843 [inline] > > __run_timers kernel/time/timer.c:2408 [inline] > > __run_timer_base+0x66a/0x8e0 kernel/time/timer.c:2419 > > run_timer_base kernel/time/timer.c:2428 [inline] > > run_timer_softirq+0xb7/0x170 kernel/time/timer.c:2438 > > __do_softirq+0x2bc/0x943 kernel/softirq.c:554 > > invoke_softirq kernel/softirq.c:428 [inline] > > __irq_exit_rcu+0xf2/0x1c0 kernel/softirq.c:633 > > irq_exit_rcu+0x9/0x30 kernel/softirq.c:645 > > instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1043 [inline] > > sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1043 > > asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702 > > memory_is_poisoned_n mm/kasan/generic.c:130 [inline] > > memory_is_poisoned mm/kasan/generic.c:161 [inline] > > check_region_inline mm/kasan/generic.c:180 [inline] > > kasan_check_range+0x4f/0x290 mm/kasan/generic.c:189 > > instrument_atomic_read_write include/linux/instrumented.h:96 [inline] > > atomic_try_cmpxchg_acquire include/linux/atomic/atomic-instrumented.h:1301 [inline] > > queued_spin_lock include/asm-generic/qspinlock.h:111 [inline] > > do_raw_spin_lock+0x14f/0x370 kernel/locking/spinlock_debug.c:116 > > spin_lock include/linux/spinlock.h:351 [inline] > > lockref_get+0x15/0x60 lib/lockref.c:50 > > dget include/linux/dcache.h:333 [inline] > > __traverse_mounts+0x3b4/0x580 fs/namei.c:1401 > > traverse_mounts fs/namei.c:1442 [inline] > > handle_mounts fs/namei.c:1545 [inline] > > step_into+0x5e5/0x1080 fs/namei.c:1842 > > walk_component fs/namei.c:2010 [inline] > > link_path_walk+0x748/0xea0 fs/namei.c:2331 > > path_lookupat+0xa9/0x450 fs/namei.c:2484 > > filename_lookup+0x256/0x610 fs/namei.c:2514 > > user_path_at_empty+0x42/0x60 fs/namei.c:2921 > > do_readlinkat+0x118/0x3b0 fs/stat.c:499 > > __do_sys_readlink fs/stat.c:532 [inline] > > __se_sys_readlink fs/stat.c:529 [inline] > > __x64_sys_readlink+0x7f/0x90 fs/stat.c:529 > > do_syscall_64+0xfb/0x240 > > entry_SYSCALL_64_after_hwframe+0x6d/0x75 > > > > -> #1 (&base->lock){-.-.}-{2:2}: > > lock_acquire+0x1e4/0x530 kernel/locking/lockdep.c:5754 > > __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline] > > _raw_spin_lock_irqsave+0xd5/0x120 kernel/locking/spinlock.c:162 > > lock_timer_base+0x112/0x240 kernel/time/timer.c:1051 > > __mod_timer+0x1ca/0xeb0 kernel/time/timer.c:1132 > > queue_delayed_work_on+0x15a/0x260 kernel/workqueue.c:2595 > > kvfree_call_rcu+0x47f/0x790 kernel/rcu/tree.c:3472 > > rtnl_register_internal+0x482/0x590 net/core/rtnetlink.c:265 > > rtnl_register+0x36/0x80 net/core/rtnetlink.c:315 > > ip_rt_init+0x2f5/0x3a0 net/ipv4/route.c:3719 > > ip_init+0xe/0x20 net/ipv4/ip_output.c:1664 > > inet_init+0x3d8/0x580 net/ipv4/af_inet.c:2022 > > do_one_initcall+0x238/0x830 init/main.c:1241 > > do_initcall_level+0x157/0x210 init/main.c:1303 > > do_initcalls+0x3f/0x80 init/main.c:1319 > > kernel_init_freeable+0x435/0x5d0 init/main.c:1550 > > kernel_init+0x1d/0x2a0 init/main.c:1439 > > ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147 > > ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:243 > > > > -> #0 (krc.lock){..-.}-{2:2}: > > check_prev_add kernel/locking/lockdep.c:3134 [inline] > > check_prevs_add kernel/locking/lockdep.c:3253 [inline] > > validate_chain+0x18cb/0x58e0 kernel/locking/lockdep.c:3869 > > __lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137 > > lock_acquire+0x1e4/0x530 kernel/locking/lockdep.c:5754 > > __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline] > > _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154 > > krc_this_cpu_lock kernel/rcu/tree.c:2960 [inline] > > add_ptr_to_bulk_krc_lock kernel/rcu/tree.c:3359 [inline] > > kvfree_call_rcu+0x18a/0x790 kernel/rcu/tree.c:3444 > > trie_update_elem+0x819/0xc10 kernel/bpf/lpm_trie.c:385 > > bpf_map_update_value+0x4d3/0x540 kernel/bpf/syscall.c:203 > > generic_map_update_batch+0x60d/0x900 kernel/bpf/syscall.c:1876 > > bpf_map_do_batch+0x3e0/0x690 kernel/bpf/syscall.c:5145 > > __sys_bpf+0x377/0x810 > > __do_sys_bpf kernel/bpf/syscall.c:5738 [inline] > > __se_sys_bpf kernel/bpf/syscall.c:5736 [inline] > > __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:5736 > > do_syscall_64+0xfb/0x240 > > entry_SYSCALL_64_after_hwframe+0x6d/0x75 > > > > other info that might help us debug this: > > > > Chain exists of: > > krc.lock --> &base->lock --> &trie->lock > > > > Possible unsafe locking scenario: > > > > CPU0 CPU1 > > ---- ---- > > lock(&trie->lock); > > lock(&base->lock); > > lock(&trie->lock); > > lock(krc.lock); > > > > *** DEADLOCK *** > > > > 2 locks held by syz-executor.3/6590: > > #0: ffffffff8e132020 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:298 [inline] > > #0: ffffffff8e132020 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:750 [inline] > > #0: ffffffff8e132020 (rcu_read_lock){....}-{1:2}, at: bpf_map_update_value+0x3c4/0x540 kernel/bpf/syscall.c:202 > > #1: ffff888021a271f8 (&trie->lock){..-.}-{2:2}, at: trie_update_elem+0xcb/0xc10 kernel/bpf/lpm_trie.c:324 > > > > stack backtrace: > > CPU: 1 PID: 6590 Comm: syz-executor.3 Not tainted 6.8.0-syzkaller-08951-gfe46a7dd189e #0 > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/29/2024 > > Call Trace: > > <TASK> > > __dump_stack lib/dump_stack.c:88 [inline] > > dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114 > > check_noncircular+0x36a/0x4a0 kernel/locking/lockdep.c:2187 > > check_prev_add kernel/locking/lockdep.c:3134 [inline] > > check_prevs_add kernel/locking/lockdep.c:3253 [inline] > > validate_chain+0x18cb/0x58e0 kernel/locking/lockdep.c:3869 > > __lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137 > > lock_acquire+0x1e4/0x530 kernel/locking/lockdep.c:5754 > > __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline] > > _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154 > > krc_this_cpu_lock kernel/rcu/tree.c:2960 [inline] > > add_ptr_to_bulk_krc_lock kernel/rcu/tree.c:3359 [inline] > > kvfree_call_rcu+0x18a/0x790 kernel/rcu/tree.c:3444 > > trie_update_elem+0x819/0xc10 kernel/bpf/lpm_trie.c:385 > > bpf_map_update_value+0x4d3/0x540 kernel/bpf/syscall.c:203 > > generic_map_update_batch+0x60d/0x900 kernel/bpf/syscall.c:1876 > > bpf_map_do_batch+0x3e0/0x690 kernel/bpf/syscall.c:5145 > > __sys_bpf+0x377/0x810 > > __do_sys_bpf kernel/bpf/syscall.c:5738 [inline] > > __se_sys_bpf kernel/bpf/syscall.c:5736 [inline] > > __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:5736 > > do_syscall_64+0xfb/0x240 > > entry_SYSCALL_64_after_hwframe+0x6d/0x75 > > RIP: 0033:0x7fe5f987dda9 > > Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 e1 20 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48 > > RSP: 002b:00007fe5fa6000c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000141 > > RAX: ffffffffffffffda RBX: 00007fe5f99abf80 RCX: 00007fe5f987dda9 > > RDX: 0000000000000038 RSI: 0000000020000240 RDI: 000000000000001a > > RBP: 00007fe5f98ca47a R08: 0000000000000000 R09: 0000000000000000 > > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 > > R13: 000000000000000b R14: 00007fe5f99abf80 R15: 00007ffe908076c8 > > </TASK> > > > > > > --- > > This report is generated by a bot. It may contain errors. > > See https://goo.gl/tpsmEJ for more information about syzbot. > > syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxx. > > > > syzbot will keep track of this issue. See: > > https://goo.gl/tpsmEJ#status for how to communicate with syzbot. > > > > If the report is already addressed, let syzbot know by replying with: > > #syz fix: exact-commit-title > > > > If you want to overwrite report's subsystems, reply with: > > #syz set subsystems: new-subsystem > > (See the list of subsystem names on the web dashboard) > > > > If the report is a duplicate of another one, reply with: > > #syz dup: exact-subject-of-another-report > > > > If you want to undo deduplication, reply with: > > #syz undup > >
