On Sun 13-10-19 14:28:06, syzbot wrote: > syzbot has found a reproducer for the following crash on: > > HEAD commit: da940012 Merge tag 'char-misc-5.4-rc3' of git://git.kernel.. > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=12cfdf4f600000 > kernel config: https://syzkaller.appspot.com/x/.config?x=2d2fd92a28d3e50 > dashboard link: https://syzkaller.appspot.com/bug?extid=f9545ab3e9f85cd43a3a > compiler: clang version 9.0.0 (/home/glider/llvm/clang > 80fee25776c2fb61e74c1ecb1a523375c2500b69) > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=148c9fc7600000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=100d3f8b600000 > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > Reported-by: syzbot+f9545ab3e9f85cd43a3a@xxxxxxxxxxxxxxxxxxxxxxxxx > > ===================================== > WARNING: bad unlock balance detected! > 5.4.0-rc2+ #0 Not tainted > ------------------------------------- > syz-executor111/7877 is trying to release lock (rcu_callback) at: > [<ffffffff81612bd4>] rcu_lock_release+0x4/0x20 include/linux/rcupdate.h:212 > but there are no more locks to release! Hum, this is really weird. Look: > other info that might help us debug this: > 1 lock held by syz-executor111/7877: > #0: ffff8880a3c600d8 (&type->s_umount_key#42/1){+.+.}, at: > alloc_super+0x15f/0x790 fs/super.c:229 > > stack backtrace: > CPU: 1 PID: 7877 Comm: syz-executor111 Not tainted 5.4.0-rc2+ #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS > Google 01/01/2011 > Call Trace: > <IRQ> > __dump_stack lib/dump_stack.c:77 [inline] > dump_stack+0x1d8/0x2f8 lib/dump_stack.c:113 > print_unlock_imbalance_bug+0x20b/0x240 kernel/locking/lockdep.c:4008 > __lock_release kernel/locking/lockdep.c:4244 [inline] > lock_release+0x473/0x780 kernel/locking/lockdep.c:4506 > rcu_lock_release+0x1c/0x20 include/linux/rcupdate.h:214 > __rcu_reclaim kernel/rcu/rcu.h:223 [inline] __rcu_reclaim_kernel() has: rcu_lock_acquire(&rcu_callback_map); if (__is_kfree_rcu_offset(offset)) { trace_rcu_invoke_kfree_callback(rn, head, offset); kfree((void *)head - offset); rcu_lock_release(&rcu_callback_map); return true; } else { trace_rcu_invoke_callback(rn, head); f = head->func; WRITE_ONCE(head->func, (rcu_callback_t)0L); f(head); rcu_lock_release(&rcu_callback_map); return false; } So RCU locking is clearly balanced there. The only possibility I can see how this can happen is that RCU callback we have called actually released rcu_callback_map but grepping the kernel doesn't show any other place where that would get released? Confused. But apparently there is even a reproducer for this so we could dig further... Honza > rcu_do_batch kernel/rcu/tree.c:2157 [inline] > rcu_core+0x84f/0x1050 kernel/rcu/tree.c:2377 > rcu_core_si+0x9/0x10 kernel/rcu/tree.c:2386 > __do_softirq+0x333/0x7c4 arch/x86/include/asm/paravirt.h:766 > invoke_softirq kernel/softirq.c:373 [inline] > irq_exit+0x227/0x230 kernel/softirq.c:413 > exiting_irq arch/x86/include/asm/apic.h:536 [inline] > smp_apic_timer_interrupt+0x113/0x280 arch/x86/kernel/apic/apic.c:1137 > apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:830 > </IRQ> > RIP: 0010:arch_local_irq_restore arch/x86/include/asm/paravirt.h:756 > [inline] > RIP: 0010:console_unlock+0xe35/0xef0 kernel/printk/printk.c:2477 > Code: 20 00 74 0c 48 c7 c7 f0 91 8a 88 e8 65 da 4f 00 48 83 3d ad fd 2d 07 > 00 0f 84 b1 00 00 00 e8 d2 9c 16 00 48 8b 7c 24 10 57 9d <0f> 1f 44 00 00 eb > 91 e8 bf 9c 16 00 eb 8a e8 b8 9c 16 00 eb 83 48 > RSP: 0018:ffff888092daf930 EFLAGS: 00000282 ORIG_RAX: ffffffffffffff13 > RAX: ffffffff815c944e RBX: 0000000000000200 RCX: ffff888094422640 > RDX: 0000000000000000 RSI: ffffffff815c8129 RDI: 0000000000000282 > RBP: ffff888092daf9f0 R08: ffff888094422640 R09: fffffbfff111a4f1 > R10: fffffbfff111a4f1 R11: 0000000000000000 R12: dffffc0000000000 > R13: 0000000000000000 R14: 0000000000000001 R15: ffffffff88a3d748 > vprintk_emit+0x239/0x3a0 kernel/printk/printk.c:1996 > vprintk_default+0x28/0x30 kernel/printk/printk.c:2023 > vprintk_func+0x158/0x170 kernel/printk/printk_safe.c:386 > printk+0x62/0x8d kernel/printk/printk.c:2056 > __ntfs_error+0x185/0x190 fs/ntfs/debug.c:89 > read_ntfs_boot_sector fs/ntfs/super.c:675 [inline] > ntfs_fill_super+0x720/0x2a40 fs/ntfs/super.c:2784 > mount_bdev+0x27c/0x390 fs/super.c:1415 > ntfs_mount+0x34/0x40 fs/ntfs/super.c:3051 > legacy_get_tree+0xf9/0x1a0 fs/fs_context.c:647 > vfs_get_tree+0x8b/0x2a0 fs/super.c:1545 > do_new_mount fs/namespace.c:2823 [inline] > do_mount+0x16c0/0x2510 fs/namespace.c:3143 > ksys_mount+0xcc/0x100 fs/namespace.c:3352 > __do_sys_mount fs/namespace.c:3366 [inline] > __se_sys_mount fs/namespace.c:3363 [inline] > __x64_sys_mount+0xbf/0xd0 fs/namespace.c:3363 > do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:290 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > RIP: 0033:0x441e99 > Code: e8 fc ad 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 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 > 0f 83 3b 0a fc ff c3 66 2e 0f 1f 84 00 00 00 00 > RSP: 002b:00007fff8d7174e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5 > RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000441e99 > RDX: 0000000020000140 RSI: 0000000020000280 RDI: 00000000200004c0 > RBP: 000000000000f000 R08: 0000000000000000 R09: 00007fff8d717698 > R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006ccdc8 > R13: 00000000006cd440 R14: 0000000000000000 R15: 0000000000000000 > -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
