af_unix: Suppress false-positive lockdep splat for spin_lock() in __unix_gc().
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-g4d200843 #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-g4d200843 #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: 47d8ac01 ("af_unix: Fix garbage collector racing against connect()") Reported-and-tested-by: syzbot+fa379358c28cc87cc307@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=fa379358c28cc87cc307Signed-off-by:Kuniyuki Iwashima <kuniyu@amazon.com> Link: https://lore.kernel.org/r/20240424170443.9832-1-kuniyu@amazon.comSigned-off-by:
Jakub Kicinski <kuba@kernel.org>
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