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SubjectRe: WARNING: bad unlock balance in rcu_core
Hi,

On Wed, Oct 16, 2019 at 02:27:07AM -0700, syzbot wrote:
> syzbot has found a reproducer for the following crash on:
>
> HEAD commit: 0e9d28bc Add linux-next specific files for 20191015
> git tree: linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=11745608e00000
> kernel config: https://syzkaller.appspot.com/x/.config?x=3d84ca04228b0bf4
> dashboard link: https://syzkaller.appspot.com/bug?extid=36baa6c2180e959e19b1
> compiler: gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=159d297f600000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16289b30e00000
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+36baa6c2180e959e19b1@syzkaller.appspotmail.com
>
> =====================================
> WARNING: bad unlock balance detected!
> 5.4.0-rc3-next-20191015 #0 Not tainted
> -------------------------------------
> syz-executor276/8897 is trying to release lock (rcu_callback) at:
> [<ffffffff8160e7a4>] __write_once_size include/linux/compiler.h:226 [inline]
> [<ffffffff8160e7a4>] __rcu_reclaim kernel/rcu/rcu.h:221 [inline]
> [<ffffffff8160e7a4>] rcu_do_batch kernel/rcu/tree.c:2157 [inline]
> [<ffffffff8160e7a4>] rcu_core+0x574/0x1560 kernel/rcu/tree.c:2377
> but there are no more locks to release!
>
> other info that might help us debug this:
> 1 lock held by syz-executor276/8897:
> #0: ffff88809a3cc0d8 (&type->s_umount_key#40/1){+.+.}, at:
> alloc_super+0x158/0x910 fs/super.c:229
>
> stack backtrace:
> CPU: 0 PID: 8897 Comm: syz-executor276 Not tainted 5.4.0-rc3-next-20191015
> #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+0x172/0x1f0 lib/dump_stack.c:113
> print_unlock_imbalance_bug kernel/locking/lockdep.c:4008 [inline]
> print_unlock_imbalance_bug.cold+0x114/0x123 kernel/locking/lockdep.c:3984
> __lock_release kernel/locking/lockdep.c:4244 [inline]
> lock_release+0x5f2/0x960 kernel/locking/lockdep.c:4505
> rcu_lock_release include/linux/rcupdate.h:213 [inline]
> __rcu_reclaim kernel/rcu/rcu.h:223 [inline]

I have little knowledge about this kind of stuff, but after seeing
the dashboard https://syzkaller.appspot.com/bug?extid=36baa6c2180e959e19b1

I guess this is highly related with ntfs, and in ntfs_fill_super, it
has lockdep_off() in ntfs_fill_super...

In detail, commit 90c1cba2b3b3 ("locking/lockdep: Zap lock classes even
with lock debugging disabled") [1], and free_zapped_rcu....

static void free_zapped_rcu(struct rcu_head *ch)
{
struct pending_free *pf;
unsigned long flags;

if (WARN_ON_ONCE(ch != &delayed_free.rcu_head))
return;

raw_local_irq_save(flags);
arch_spin_lock(&lockdep_lock);
current->lockdep_recursion = 1; <--- here

/* closed head */
pf = delayed_free.pf + (delayed_free.index ^ 1);
__free_zapped_classes(pf);
delayed_free.scheduled = false;

/*
* If there's anything on the open list, close and start a new callback.
*/
call_rcu_zapped(delayed_free.pf + delayed_free.index);

current->lockdep_recursion = 0;
arch_spin_unlock(&lockdep_lock);
raw_local_irq_restore(flags);
}

Completely guess and untest since I am not familar with that,
but in case of that, Cc related people...
If I'm wrong, ignore my comments and unintentional noise....

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=90c1cba2b3b3851c151229f61801919b2904d437

Thanks,
Gao Xiang

> rcu_do_batch kernel/rcu/tree.c:2157 [inline]
> rcu_core+0x594/0x1560 kernel/rcu/tree.c:2377
> rcu_core_si+0x9/0x10 kernel/rcu/tree.c:2386
> __do_softirq+0x262/0x98c kernel/softirq.c:292
> invoke_softirq kernel/softirq.c:373 [inline]
> irq_exit+0x19b/0x1e0 kernel/softirq.c:413
> exiting_irq arch/x86/include/asm/apic.h:536 [inline]
> smp_apic_timer_interrupt+0x1a3/0x610 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+0xbb8/0xf00 kernel/printk/printk.c:2481
> Code: f3 88 48 c1 e8 03 42 80 3c 30 00 0f 85 e4 02 00 00 48 83 3d 99 9c 96
> 07 00 0f 84 91 01 00 00 e8 be c4 16 00 48 8b 7d 98 57 9d <0f> 1f 44 00 00 e9
> 6d ff ff ff e8 a9 c4 16 00 48 8b 7d 08 c7 05 eb
> RSP: 0018:ffff88809fd7f8f0 EFLAGS: 00000293 ORIG_RAX: ffffffffffffff13
> RAX: ffff8880a8bee540 RBX: 0000000000000200 RCX: 1ffffffff138eea6
> RDX: 0000000000000000 RSI: ffffffff815c8592 RDI: 0000000000000293
> RBP: ffff88809fd7f978 R08: ffff8880a8bee540 R09: fffffbfff11f4119
> R10: fffffbfff11f4118 R11: 0000000000000001 R12: 0000000000000000
> R13: ffffffff843f8ca0 R14: dffffc0000000000 R15: ffffffff895e1130
> vprintk_emit+0x2a0/0x700 kernel/printk/printk.c:1996
> vprintk_default+0x28/0x30 kernel/printk/printk.c:2023
> vprintk_func+0x7e/0x189 kernel/printk/printk_safe.c:386
> printk+0xba/0xed kernel/printk/printk.c:2056
> __ntfs_error.cold+0x91/0xc7 fs/ntfs/debug.c:89
> read_ntfs_boot_sector fs/ntfs/super.c:682 [inline]
> ntfs_fill_super+0x1ad3/0x3160 fs/ntfs/super.c:2784
> mount_bdev+0x304/0x3c0 fs/super.c:1415
> ntfs_mount+0x35/0x40 fs/ntfs/super.c:3051
> legacy_get_tree+0x108/0x220 fs/fs_context.c:647
> vfs_get_tree+0x8e/0x300 fs/super.c:1545
> do_new_mount fs/namespace.c:2823 [inline]
> do_mount+0x142e/0x1cf0 fs/namespace.c:3143
> ksys_mount+0xdb/0x150 fs/namespace.c:3352
> __do_sys_mount fs/namespace.c:3366 [inline]
> __se_sys_mount fs/namespace.c:3363 [inline]
> __x64_sys_mount+0xbe/0x150 fs/namespace.c:3363
> do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x4411a9
> Code: e8 fc ab 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 9b 09 fc ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007ffffff57cf8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00000000004411a9
> RDX: 0000000020000140 RSI: 0000000020000280 RDI: 00000000200004c0
> RBP: 00000000000114e0 R08: 0000000000000000 R09: 00000000004002c8
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000401fd0
> R13: 0000000000402060 R14: 0000000000000000 R15: 0000000000000000
>

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