On 12/8/25 12:21, syzbot wrote: > Hello, > > syzbot found the following issue on: > > HEAD commit: 559e608c4655 Merge tag 'ntfs3_for_6.19' of https://github... > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=164fdcc2580000 > kernel config: https://syzkaller.appspot.com/x/.config?x=74c2ec4187efdce > dashboard link: https://syzkaller.appspot.com/bug?extid=b1546ad4a95331b2101e > compiler: Debian clang version 20.1.8 > (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8 > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1446301a580000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=112c3f42580000 > > Downloadable assets: > disk image: > https://storage.googleapis.com/syzbot-assets/7d28798cb263/disk-559e608c.raw.xz > vmlinux: > https://storage.googleapis.com/syzbot-assets/239e800627b8/vmlinux-559e608c.xz > kernel image: > https://storage.googleapis.com/syzbot-assets/e89da2cc9887/bzImage-559e608c.xz
> The issue was bisected to: > > commit 0db4941d9dae159d887e7e2eac7e54e60c3aac87 > Author: Fushuai Wang <[email protected]> > Date: Tue Oct 7 07:40:11 2025 +0000 > > bpf: Use rcu_read_lock_dont_migrate in bpf_sk_storage.c (came here because reviewing a proposed fix: https://lore.kernel.org/all/[email protected]/ ) The bisection result seem weird to me, it changes some usages of migrate_disable(); + rcu_read_lock(); to rcu_read_lock_dont_migrate(); However with CONFIG_PREEMPT_RCU=y which the syzbot .config has, this should be equivalent? (Also I'm not sure the affected paths are even in the backtrace?) In either case with CONFIG_PREEMPT_RCU=y, rcu_read_lock() should not be disabling preemption? > > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=10cd3c1a580000 > final oops: https://syzkaller.appspot.com/x/report.txt?x=12cd3c1a580000 > console output: https://syzkaller.appspot.com/x/log.txt?x=14cd3c1a580000 > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: [email protected] > Fixes: 0db4941d9dae ("bpf: Use rcu_read_lock_dont_migrate in > bpf_sk_storage.c") > > BUG: sleeping function called from invalid context at > kernel/locking/spinlock_rt.c:48 > in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 6128, name: syz.3.73 > preempt_count: 2, expected: 0 > RCU nest depth: 1, expected: 1 > 3 locks held by syz.3.73/6128: > #0: ffff8880493da398 (sk_lock-AF_VSOCK){+.+.}-{0:0}, at: lock_sock > include/net/sock.h:1700 [inline] > #0: ffff8880493da398 (sk_lock-AF_VSOCK){+.+.}-{0:0}, at: > vsock_connect+0x152/0xd40 net/vmw_vsock/af_vsock.c:1546 > #1: ffffffff8d5aeba0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire > include/linux/rcupdate.h:331 [inline] > #1: ffffffff8d5aeba0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock > include/linux/rcupdate.h:867 [inline] > #1: ffffffff8d5aeba0 (rcu_read_lock){....}-{1:3}, at: __bpf_trace_run > kernel/trace/bpf_trace.c:2074 [inline] > #1: ffffffff8d5aeba0 (rcu_read_lock){....}-{1:3}, at: > bpf_trace_run9+0x1ec/0x510 kernel/trace/bpf_trace.c:2123 > #2: ffff8880b893fd48 (&s->lock_key#14){+.+.}-{3:3}, at: spin_lock > include/linux/spinlock_rt.h:44 [inline] > #2: ffff8880b893fd48 (&s->lock_key#14){+.+.}-{3:3}, at: > ___slab_alloc+0x12f/0x1400 mm/slub.c:4516 > Preemption disabled at: > [<ffffffff82179f5a>] class_preempt_constructor include/linux/preempt.h:468 > [inline] > [<ffffffff82179f5a>] __migrate_enable include/linux/sched.h:2378 [inline] > [<ffffffff82179f5a>] migrate_enable include/linux/sched.h:2429 [inline] > [<ffffffff82179f5a>] __slab_alloc+0xea/0x1f0 mm/slub.c:4777 Wait, so it's slab code itself disabling preemption, in migrate_enable()? But there's guard(preempt)(); so it should be enabled again. Or is it the limitation of the reporting, that it doesn't know which preemptions were re-enabled and which not? > CPU: 1 UID: 0 PID: 6128 Comm: syz.3.73 Not tainted syzkaller #0 > PREEMPT_{RT,(full)} > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS > Google 10/25/2025 > Call Trace: > <TASK> > dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120 > __might_resched+0x44b/0x5d0 kernel/sched/core.c:8830 > __rt_spin_lock kernel/locking/spinlock_rt.c:48 [inline] > rt_spin_lock+0xc7/0x3e0 kernel/locking/spinlock_rt.c:57 > spin_lock include/linux/spinlock_rt.h:44 [inline] > ___slab_alloc+0x12f/0x1400 mm/slub.c:4516 > __slab_alloc+0xc6/0x1f0 mm/slub.c:4774 > __slab_alloc_node mm/slub.c:4850 [inline] > kmalloc_nolock_noprof+0x1be/0x440 mm/slub.c:5729 > bpf_stream_elem_alloc kernel/bpf/stream.c:33 [inline] > __bpf_stream_push_str+0xa8/0x2b0 kernel/bpf/stream.c:50 > bpf_stream_stage_printk+0x14e/0x1c0 kernel/bpf/stream.c:306 > bpf_prog_report_may_goto_violation+0xc4/0x190 kernel/bpf/core.c:3203 > bpf_check_timed_may_goto+0xaa/0xb0 kernel/bpf/core.c:3221 > arch_bpf_timed_may_goto+0x21/0x40 arch/x86/net/bpf_timed_may_goto.S:40 > bpf_prog_262a74d054ad2993+0x53/0x5f > bpf_dispatcher_nop_func include/linux/bpf.h:1376 [inline] > __bpf_prog_run include/linux/filter.h:723 [inline] > bpf_prog_run include/linux/filter.h:730 [inline] > __bpf_trace_run kernel/trace/bpf_trace.c:2075 [inline] > bpf_trace_run9+0x2de/0x510 kernel/trace/bpf_trace.c:2123 > __bpf_trace_virtio_transport_alloc_pkt+0x2d7/0x340 > include/trace/events/vsock_virtio_transport_common.h:39 > __do_trace_virtio_transport_alloc_pkt > include/trace/events/vsock_virtio_transport_common.h:39 [inline] > trace_virtio_transport_alloc_pkt > include/trace/events/vsock_virtio_transport_common.h:39 [inline] > virtio_transport_alloc_skb+0x10af/0x1110 > net/vmw_vsock/virtio_transport_common.c:311 > virtio_transport_send_pkt_info+0x694/0x10b0 > net/vmw_vsock/virtio_transport_common.c:390 > virtio_transport_connect+0xa7/0x100 > net/vmw_vsock/virtio_transport_common.c:1072 > vsock_connect+0xaca/0xd40 net/vmw_vsock/af_vsock.c:1611 > __sys_connect_file net/socket.c:2080 [inline] > __sys_connect+0x323/0x450 net/socket.c:2099 > __do_sys_connect net/socket.c:2105 [inline] > __se_sys_connect net/socket.c:2102 [inline] > __x64_sys_connect+0x7a/0x90 net/socket.c:2102 > do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] > do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > RIP: 0033:0x7f0c4d91f749 > Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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 a8 ff ff ff f7 d8 64 89 01 48 > RSP: 002b:00007ffd8ed26ac8 EFLAGS: 00000246 ORIG_RAX: 000000000000002a > RAX: ffffffffffffffda RBX: 00007f0c4db75fa0 RCX: 00007f0c4d91f749 > RDX: 0000000000000010 RSI: 0000200000000080 RDI: 0000000000000003 > RBP: 00007f0c4d9a3f91 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 > R13: 00007f0c4db75fa0 R14: 00007f0c4db75fa0 R15: 0000000000000003 > </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 [email protected]. > > syzbot will keep track of this issue. See: > https://goo.gl/tpsmEJ#status for how to communicate with syzbot. > For information about bisection process see: https://goo.gl/tpsmEJ#bisection > > If the report is already addressed, let syzbot know by replying with: > #syz fix: exact-commit-title > > If you want syzbot to run the reproducer, reply with: > #syz test: git://repo/address.git branch-or-commit-hash > If you attach or paste a git patch, syzbot will apply it before testing. > > 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 >
