diff mbox series

[v2,net] af_unix: Suppress false-positive lockdep splat for spin_lock() in __unix_gc().

Message ID 20240424022319.20574-1-kuniyu@amazon.com (mailing list archive)
State Superseded
Delegated to: Netdev Maintainers
Headers show
Series [v2,net] af_unix: Suppress false-positive lockdep splat for spin_lock() in __unix_gc(). | expand

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netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 950 this patch: 950
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netdev/checkpatch warning WARNING: Possible repeated word: 'Google'
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Commit Message

Kuniyuki Iwashima April 24, 2024, 2:23 a.m. UTC
syzbot reported a lockdep splat regarding unix_gc_lock() and
unix_state_lock().

One is called from recvmsg() for a connected socket, and another
is called from GC for TCP_LISTEN socket.

So, the splat is false-positive.

Let's add a dedicated lock class for the latter to suppress the splat.

Note that this change is not necessary for net-next.git as the issue
is only applied to the old GC impl.

[0]:
WARNING: possible circular locking dependency detected
6.9.0-rc5-syzkaller-00007-g4d2008430ce8 #0 Not tainted
 -----------------------------------------------------
kworker/u8:1/11 is trying to acquire lock:
ffff88807cea4e70 (&u->lock){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
ffff88807cea4e70 (&u->lock){+.+.}-{2:2}, at: __unix_gc+0x40e/0xf70 net/unix/garbage.c:302

but task is already holding lock:
ffffffff8f6ab638 (unix_gc_lock){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
ffffffff8f6ab638 (unix_gc_lock){+.+.}-{2:2}, at: __unix_gc+0x117/0xf70 net/unix/garbage.c:261

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

 -> #1 (unix_gc_lock){+.+.}-{2:2}:
       lock_acquire+0x1ed/0x550 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
       spin_lock include/linux/spinlock.h:351 [inline]
       unix_notinflight+0x13d/0x390 net/unix/garbage.c:140
       unix_detach_fds net/unix/af_unix.c:1819 [inline]
       unix_destruct_scm+0x221/0x350 net/unix/af_unix.c:1876
       skb_release_head_state+0x100/0x250 net/core/skbuff.c:1188
       skb_release_all net/core/skbuff.c:1200 [inline]
       __kfree_skb net/core/skbuff.c:1216 [inline]
       kfree_skb_reason+0x16d/0x3b0 net/core/skbuff.c:1252
       kfree_skb include/linux/skbuff.h:1262 [inline]
       manage_oob net/unix/af_unix.c:2672 [inline]
       unix_stream_read_generic+0x1125/0x2700 net/unix/af_unix.c:2749
       unix_stream_splice_read+0x239/0x320 net/unix/af_unix.c:2981
       do_splice_read fs/splice.c:985 [inline]
       splice_file_to_pipe+0x299/0x500 fs/splice.c:1295
       do_splice+0xf2d/0x1880 fs/splice.c:1379
       __do_splice fs/splice.c:1436 [inline]
       __do_sys_splice fs/splice.c:1652 [inline]
       __se_sys_splice+0x331/0x4a0 fs/splice.c:1634
       do_syscall_x64 arch/x86/entry/common.c:52 [inline]
       do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

 -> #0 (&u->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+0x1ed/0x550 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
       spin_lock include/linux/spinlock.h:351 [inline]
       __unix_gc+0x40e/0xf70 net/unix/garbage.c:302
       process_one_work kernel/workqueue.c:3254 [inline]
       process_scheduled_works+0xa10/0x17c0 kernel/workqueue.c:3335
       worker_thread+0x86d/0xd70 kernel/workqueue.c:3416
       kthread+0x2f0/0x390 kernel/kthread.c:388
       ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(unix_gc_lock);
                               lock(&u->lock);
                               lock(unix_gc_lock);
  lock(&u->lock);

 *** DEADLOCK ***

3 locks held by kworker/u8:1/11:
 #0: ffff888015089148 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3229 [inline]
 #0: ffff888015089148 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_scheduled_works+0x8e0/0x17c0 kernel/workqueue.c:3335
 #1: ffffc90000107d00 (unix_gc_work){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3230 [inline]
 #1: ffffc90000107d00 (unix_gc_work){+.+.}-{0:0}, at: process_scheduled_works+0x91b/0x17c0 kernel/workqueue.c:3335
 #2: ffffffff8f6ab638 (unix_gc_lock){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
 #2: ffffffff8f6ab638 (unix_gc_lock){+.+.}-{2:2}, at: __unix_gc+0x117/0xf70 net/unix/garbage.c:261

stack backtrace:
CPU: 0 PID: 11 Comm: kworker/u8:1 Not tainted 6.9.0-rc5-syzkaller-00007-g4d2008430ce8 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
Workqueue: events_unbound __unix_gc
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+0x1ed/0x550 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
 spin_lock include/linux/spinlock.h:351 [inline]
 __unix_gc+0x40e/0xf70 net/unix/garbage.c:302
 process_one_work kernel/workqueue.c:3254 [inline]
 process_scheduled_works+0xa10/0x17c0 kernel/workqueue.c:3335
 worker_thread+0x86d/0xd70 kernel/workqueue.c:3416
 kthread+0x2f0/0x390 kernel/kthread.c:388
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>

Fixes: 47d8ac011fe1 ("af_unix: Fix garbage collector racing against connect()")
Reported-and-tested-by: syzbot+fa379358c28cc87cc307@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=fa379358c28cc87cc307
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
---
 include/net/af_unix.h | 3 +++
 net/unix/garbage.c    | 2 +-
 2 files changed, 4 insertions(+), 1 deletion(-)

Comments

Michal Luczaj April 24, 2024, 12:35 p.m. UTC | #1
On 4/24/24 04:23, Kuniyuki Iwashima wrote:
> syzbot reported a lockdep splat regarding unix_gc_lock() and
> unix_state_lock().

Just a nit: probably unix_gc_lock, without brackets?

Thanks!
Michal

> One is called from recvmsg() for a connected socket, and another
> is called from GC for TCP_LISTEN socket.
> 
> So, the splat is false-positive.
> 
> Let's add a dedicated lock class for the latter to suppress the splat.
> 
> Note that this change is not necessary for net-next.git as the issue
> is only applied to the old GC impl.
> 
> [0]:
> WARNING: possible circular locking dependency detected
> 6.9.0-rc5-syzkaller-00007-g4d2008430ce8 #0 Not tainted
>  -----------------------------------------------------
> kworker/u8:1/11 is trying to acquire lock:
> ffff88807cea4e70 (&u->lock){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
> ffff88807cea4e70 (&u->lock){+.+.}-{2:2}, at: __unix_gc+0x40e/0xf70 net/unix/garbage.c:302
> 
> but task is already holding lock:
> ffffffff8f6ab638 (unix_gc_lock){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
> ffffffff8f6ab638 (unix_gc_lock){+.+.}-{2:2}, at: __unix_gc+0x117/0xf70 net/unix/garbage.c:261
> 
> which lock already depends on the new lock.
> 
> the existing dependency chain (in reverse order) is:
> 
>  -> #1 (unix_gc_lock){+.+.}-{2:2}:
>        lock_acquire+0x1ed/0x550 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
>        spin_lock include/linux/spinlock.h:351 [inline]
>        unix_notinflight+0x13d/0x390 net/unix/garbage.c:140
>        unix_detach_fds net/unix/af_unix.c:1819 [inline]
>        unix_destruct_scm+0x221/0x350 net/unix/af_unix.c:1876
>        skb_release_head_state+0x100/0x250 net/core/skbuff.c:1188
>        skb_release_all net/core/skbuff.c:1200 [inline]
>        __kfree_skb net/core/skbuff.c:1216 [inline]
>        kfree_skb_reason+0x16d/0x3b0 net/core/skbuff.c:1252
>        kfree_skb include/linux/skbuff.h:1262 [inline]
>        manage_oob net/unix/af_unix.c:2672 [inline]
>        unix_stream_read_generic+0x1125/0x2700 net/unix/af_unix.c:2749
>        unix_stream_splice_read+0x239/0x320 net/unix/af_unix.c:2981
>        do_splice_read fs/splice.c:985 [inline]
>        splice_file_to_pipe+0x299/0x500 fs/splice.c:1295
>        do_splice+0xf2d/0x1880 fs/splice.c:1379
>        __do_splice fs/splice.c:1436 [inline]
>        __do_sys_splice fs/splice.c:1652 [inline]
>        __se_sys_splice+0x331/0x4a0 fs/splice.c:1634
>        do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>        do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83
>        entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
>  -> #0 (&u->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+0x1ed/0x550 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
>        spin_lock include/linux/spinlock.h:351 [inline]
>        __unix_gc+0x40e/0xf70 net/unix/garbage.c:302
>        process_one_work kernel/workqueue.c:3254 [inline]
>        process_scheduled_works+0xa10/0x17c0 kernel/workqueue.c:3335
>        worker_thread+0x86d/0xd70 kernel/workqueue.c:3416
>        kthread+0x2f0/0x390 kernel/kthread.c:388
>        ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
>        ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
> 
> other info that might help us debug this:
> 
>  Possible unsafe locking scenario:
> 
>        CPU0                    CPU1
>        ----                    ----
>   lock(unix_gc_lock);
>                                lock(&u->lock);
>                                lock(unix_gc_lock);
>   lock(&u->lock);
> 
>  *** DEADLOCK ***
> 
> 3 locks held by kworker/u8:1/11:
>  #0: ffff888015089148 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3229 [inline]
>  #0: ffff888015089148 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_scheduled_works+0x8e0/0x17c0 kernel/workqueue.c:3335
>  #1: ffffc90000107d00 (unix_gc_work){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3230 [inline]
>  #1: ffffc90000107d00 (unix_gc_work){+.+.}-{0:0}, at: process_scheduled_works+0x91b/0x17c0 kernel/workqueue.c:3335
>  #2: ffffffff8f6ab638 (unix_gc_lock){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
>  #2: ffffffff8f6ab638 (unix_gc_lock){+.+.}-{2:2}, at: __unix_gc+0x117/0xf70 net/unix/garbage.c:261
> 
> stack backtrace:
> CPU: 0 PID: 11 Comm: kworker/u8:1 Not tainted 6.9.0-rc5-syzkaller-00007-g4d2008430ce8 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
> Workqueue: events_unbound __unix_gc
> 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+0x1ed/0x550 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
>  spin_lock include/linux/spinlock.h:351 [inline]
>  __unix_gc+0x40e/0xf70 net/unix/garbage.c:302
>  process_one_work kernel/workqueue.c:3254 [inline]
>  process_scheduled_works+0xa10/0x17c0 kernel/workqueue.c:3335
>  worker_thread+0x86d/0xd70 kernel/workqueue.c:3416
>  kthread+0x2f0/0x390 kernel/kthread.c:388
>  ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
>  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
>  </TASK>
> 
> Fixes: 47d8ac011fe1 ("af_unix: Fix garbage collector racing against connect()")
> Reported-and-tested-by: syzbot+fa379358c28cc87cc307@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=fa379358c28cc87cc307
> Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
> ---
>  include/net/af_unix.h | 3 +++
>  net/unix/garbage.c    | 2 +-
>  2 files changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/include/net/af_unix.h b/include/net/af_unix.h
> index 627ea8e2d915..3dee0b2721aa 100644
> --- a/include/net/af_unix.h
> +++ b/include/net/af_unix.h
> @@ -85,6 +85,9 @@ enum unix_socket_lock_class {
>  	U_LOCK_NORMAL,
>  	U_LOCK_SECOND,	/* for double locking, see unix_state_double_lock(). */
>  	U_LOCK_DIAG, /* used while dumping icons, see sk_diag_dump_icons(). */
> +	U_LOCK_GC_LISTENER, /* used for listening socket while determining gc
> +			     * candidates to close a small race window.
> +			     */
>  };
>  
>  static inline void unix_state_lock_nested(struct sock *sk,
> diff --git a/net/unix/garbage.c b/net/unix/garbage.c
> index 6433a414acf8..0104be9d4704 100644
> --- a/net/unix/garbage.c
> +++ b/net/unix/garbage.c
> @@ -299,7 +299,7 @@ static void __unix_gc(struct work_struct *work)
>  			__set_bit(UNIX_GC_MAYBE_CYCLE, &u->gc_flags);
>  
>  			if (sk->sk_state == TCP_LISTEN) {
> -				unix_state_lock(sk);
> +				unix_state_lock_nested(sk, U_LOCK_GC_LISTENER);
>  				unix_state_unlock(sk);
>  			}
>  		}
Kuniyuki Iwashima April 24, 2024, 4:59 p.m. UTC | #2
From: Michal Luczaj <mhal@rbox.co>
Date: Wed, 24 Apr 2024 14:35:19 +0200
> On 4/24/24 04:23, Kuniyuki Iwashima wrote:
> > syzbot reported a lockdep splat regarding unix_gc_lock() and
> > unix_state_lock().
> 
> Just a nit: probably unix_gc_lock, without brackets?

Ah, nice catch :)

Will fix, thanks!

pw-bot: cr
diff mbox series

Patch

diff --git a/include/net/af_unix.h b/include/net/af_unix.h
index 627ea8e2d915..3dee0b2721aa 100644
--- a/include/net/af_unix.h
+++ b/include/net/af_unix.h
@@ -85,6 +85,9 @@  enum unix_socket_lock_class {
 	U_LOCK_NORMAL,
 	U_LOCK_SECOND,	/* for double locking, see unix_state_double_lock(). */
 	U_LOCK_DIAG, /* used while dumping icons, see sk_diag_dump_icons(). */
+	U_LOCK_GC_LISTENER, /* used for listening socket while determining gc
+			     * candidates to close a small race window.
+			     */
 };
 
 static inline void unix_state_lock_nested(struct sock *sk,
diff --git a/net/unix/garbage.c b/net/unix/garbage.c
index 6433a414acf8..0104be9d4704 100644
--- a/net/unix/garbage.c
+++ b/net/unix/garbage.c
@@ -299,7 +299,7 @@  static void __unix_gc(struct work_struct *work)
 			__set_bit(UNIX_GC_MAYBE_CYCLE, &u->gc_flags);
 
 			if (sk->sk_state == TCP_LISTEN) {
-				unix_state_lock(sk);
+				unix_state_lock_nested(sk, U_LOCK_GC_LISTENER);
 				unix_state_unlock(sk);
 			}
 		}