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| 1 | +af_unix: Suppress false-positive lockdep splat for spin_lock() in __unix_gc(). |
| 2 | + |
| 3 | +jira LE-2015 |
| 4 | +Rebuild_History Non-Buildable kernel-5.14.0-427.42.1.el9_4 |
| 5 | +commit-author Kuniyuki Iwashima < [email protected]> |
| 6 | +commit 1971d13ffa84a551d29a81fdf5b5ec5be166ac83 |
| 7 | +Empty-Commit: Cherry-Pick Conflicts during history rebuild. |
| 8 | +Will be included in final tarball splat. Ref for failed cherry-pick at: |
| 9 | +ciq/ciq_backports/kernel-5.14.0-427.42.1.el9_4/1971d13f.failed |
| 10 | + |
| 11 | +syzbot reported a lockdep splat regarding unix_gc_lock and |
| 12 | +unix_state_lock(). |
| 13 | + |
| 14 | +One is called from recvmsg() for a connected socket, and another |
| 15 | +is called from GC for TCP_LISTEN socket. |
| 16 | + |
| 17 | +So, the splat is false-positive. |
| 18 | + |
| 19 | +Let's add a dedicated lock class for the latter to suppress the splat. |
| 20 | + |
| 21 | +Note that this change is not necessary for net-next.git as the issue |
| 22 | +is only applied to the old GC impl. |
| 23 | + |
| 24 | +[0]: |
| 25 | +WARNING: possible circular locking dependency detected |
| 26 | +6.9.0-rc5-syzkaller-00007-g4d2008430ce8 #0 Not tainted |
| 27 | + ----------------------------------------------------- |
| 28 | +kworker/u8:1/11 is trying to acquire lock: |
| 29 | +ffff88807cea4e70 (&u->lock){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline] |
| 30 | +ffff88807cea4e70 (&u->lock){+.+.}-{2:2}, at: __unix_gc+0x40e/0xf70 net/unix/garbage.c:302 |
| 31 | + |
| 32 | +but task is already holding lock: |
| 33 | +ffffffff8f6ab638 (unix_gc_lock){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline] |
| 34 | +ffffffff8f6ab638 (unix_gc_lock){+.+.}-{2:2}, at: __unix_gc+0x117/0xf70 net/unix/garbage.c:261 |
| 35 | + |
| 36 | +which lock already depends on the new lock. |
| 37 | + |
| 38 | +the existing dependency chain (in reverse order) is: |
| 39 | + |
| 40 | + -> #1 (unix_gc_lock){+.+.}-{2:2}: |
| 41 | + lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754 |
| 42 | + __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline] |
| 43 | + _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154 |
| 44 | + spin_lock include/linux/spinlock.h:351 [inline] |
| 45 | + unix_notinflight+0x13d/0x390 net/unix/garbage.c:140 |
| 46 | + unix_detach_fds net/unix/af_unix.c:1819 [inline] |
| 47 | + unix_destruct_scm+0x221/0x350 net/unix/af_unix.c:1876 |
| 48 | + skb_release_head_state+0x100/0x250 net/core/skbuff.c:1188 |
| 49 | + skb_release_all net/core/skbuff.c:1200 [inline] |
| 50 | + __kfree_skb net/core/skbuff.c:1216 [inline] |
| 51 | + kfree_skb_reason+0x16d/0x3b0 net/core/skbuff.c:1252 |
| 52 | + kfree_skb include/linux/skbuff.h:1262 [inline] |
| 53 | + manage_oob net/unix/af_unix.c:2672 [inline] |
| 54 | + unix_stream_read_generic+0x1125/0x2700 net/unix/af_unix.c:2749 |
| 55 | + unix_stream_splice_read+0x239/0x320 net/unix/af_unix.c:2981 |
| 56 | + do_splice_read fs/splice.c:985 [inline] |
| 57 | + splice_file_to_pipe+0x299/0x500 fs/splice.c:1295 |
| 58 | + do_splice+0xf2d/0x1880 fs/splice.c:1379 |
| 59 | + __do_splice fs/splice.c:1436 [inline] |
| 60 | + __do_sys_splice fs/splice.c:1652 [inline] |
| 61 | + __se_sys_splice+0x331/0x4a0 fs/splice.c:1634 |
| 62 | + do_syscall_x64 arch/x86/entry/common.c:52 [inline] |
| 63 | + do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83 |
| 64 | + entry_SYSCALL_64_after_hwframe+0x77/0x7f |
| 65 | + |
| 66 | + -> #0 (&u->lock){+.+.}-{2:2}: |
| 67 | + check_prev_add kernel/locking/lockdep.c:3134 [inline] |
| 68 | + check_prevs_add kernel/locking/lockdep.c:3253 [inline] |
| 69 | + validate_chain+0x18cb/0x58e0 kernel/locking/lockdep.c:3869 |
| 70 | + __lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137 |
| 71 | + lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754 |
| 72 | + __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline] |
| 73 | + _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154 |
| 74 | + spin_lock include/linux/spinlock.h:351 [inline] |
| 75 | + __unix_gc+0x40e/0xf70 net/unix/garbage.c:302 |
| 76 | + process_one_work kernel/workqueue.c:3254 [inline] |
| 77 | + process_scheduled_works+0xa10/0x17c0 kernel/workqueue.c:3335 |
| 78 | + worker_thread+0x86d/0xd70 kernel/workqueue.c:3416 |
| 79 | + kthread+0x2f0/0x390 kernel/kthread.c:388 |
| 80 | + ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147 |
| 81 | + ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244 |
| 82 | + |
| 83 | +other info that might help us debug this: |
| 84 | + |
| 85 | + Possible unsafe locking scenario: |
| 86 | + |
| 87 | + CPU0 CPU1 |
| 88 | + ---- ---- |
| 89 | + lock(unix_gc_lock); |
| 90 | + lock(&u->lock); |
| 91 | + lock(unix_gc_lock); |
| 92 | + lock(&u->lock); |
| 93 | + |
| 94 | + *** DEADLOCK *** |
| 95 | + |
| 96 | +3 locks held by kworker/u8:1/11: |
| 97 | + #0: ffff888015089148 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3229 [inline] |
| 98 | + #0: ffff888015089148 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_scheduled_works+0x8e0/0x17c0 kernel/workqueue.c:3335 |
| 99 | + #1: ffffc90000107d00 (unix_gc_work){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3230 [inline] |
| 100 | + #1: ffffc90000107d00 (unix_gc_work){+.+.}-{0:0}, at: process_scheduled_works+0x91b/0x17c0 kernel/workqueue.c:3335 |
| 101 | + #2: ffffffff8f6ab638 (unix_gc_lock){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline] |
| 102 | + #2: ffffffff8f6ab638 (unix_gc_lock){+.+.}-{2:2}, at: __unix_gc+0x117/0xf70 net/unix/garbage.c:261 |
| 103 | + |
| 104 | +stack backtrace: |
| 105 | +CPU: 0 PID: 11 Comm: kworker/u8:1 Not tainted 6.9.0-rc5-syzkaller-00007-g4d2008430ce8 #0 |
| 106 | +Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024 |
| 107 | +Workqueue: events_unbound __unix_gc |
| 108 | +Call Trace: |
| 109 | + <TASK> |
| 110 | + __dump_stack lib/dump_stack.c:88 [inline] |
| 111 | + dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114 |
| 112 | + check_noncircular+0x36a/0x4a0 kernel/locking/lockdep.c:2187 |
| 113 | + check_prev_add kernel/locking/lockdep.c:3134 [inline] |
| 114 | + check_prevs_add kernel/locking/lockdep.c:3253 [inline] |
| 115 | + validate_chain+0x18cb/0x58e0 kernel/locking/lockdep.c:3869 |
| 116 | + __lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137 |
| 117 | + lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754 |
| 118 | + __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline] |
| 119 | + _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154 |
| 120 | + spin_lock include/linux/spinlock.h:351 [inline] |
| 121 | + __unix_gc+0x40e/0xf70 net/unix/garbage.c:302 |
| 122 | + process_one_work kernel/workqueue.c:3254 [inline] |
| 123 | + process_scheduled_works+0xa10/0x17c0 kernel/workqueue.c:3335 |
| 124 | + worker_thread+0x86d/0xd70 kernel/workqueue.c:3416 |
| 125 | + kthread+0x2f0/0x390 kernel/kthread.c:388 |
| 126 | + ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147 |
| 127 | + ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244 |
| 128 | + </TASK> |
| 129 | + |
| 130 | +Fixes: 47d8ac011fe1 ("af_unix: Fix garbage collector racing against connect()") |
| 131 | +Reported-and-tested-by: [email protected] |
| 132 | +Closes: https://syzkaller.appspot.com/bug?extid=fa379358c28cc87cc307 |
| 133 | + Signed-off-by: Kuniyuki Iwashima < [email protected]> |
| 134 | +Link: https://lore.kernel.org/r/ [email protected] |
| 135 | + Signed-off-by: Jakub Kicinski < [email protected]> |
| 136 | +(cherry picked from commit 1971d13ffa84a551d29a81fdf5b5ec5be166ac83) |
| 137 | + Signed-off-by: Jonathan Maple < [email protected]> |
| 138 | + |
| 139 | +# Conflicts: |
| 140 | +# net/unix/garbage.c |
| 141 | +diff --cc net/unix/garbage.c |
| 142 | +index 2405f0f9af31,0104be9d4704..000000000000 |
| 143 | +--- a/net/unix/garbage.c |
| 144 | ++++ b/net/unix/garbage.c |
| 145 | +@@@ -248,6 -297,11 +248,14 @@@ void unix_gc(void |
| 146 | + list_move_tail(&u->link, &gc_candidates); |
| 147 | + __set_bit(UNIX_GC_CANDIDATE, &u->gc_flags); |
| 148 | + __set_bit(UNIX_GC_MAYBE_CYCLE, &u->gc_flags); |
| 149 | +++<<<<<<< HEAD |
| 150 | +++======= |
| 151 | ++ |
| 152 | ++ if (sk->sk_state == TCP_LISTEN) { |
| 153 | ++ unix_state_lock_nested(sk, U_LOCK_GC_LISTENER); |
| 154 | ++ unix_state_unlock(sk); |
| 155 | ++ } |
| 156 | +++>>>>>>> 1971d13ffa84 (af_unix: Suppress false-positive lockdep splat for spin_lock() in __unix_gc().) |
| 157 | + } |
| 158 | + } |
| 159 | + |
| 160 | +diff --git a/include/net/af_unix.h b/include/net/af_unix.h |
| 161 | +index 8b0dd4b52c1b..3697799f3b0c 100644 |
| 162 | +--- a/include/net/af_unix.h |
| 163 | ++++ b/include/net/af_unix.h |
| 164 | +@@ -77,6 +77,9 @@ enum unix_socket_lock_class { |
| 165 | + U_LOCK_NORMAL, |
| 166 | + U_LOCK_SECOND, /* for double locking, see unix_state_double_lock(). */ |
| 167 | + U_LOCK_DIAG, /* used while dumping icons, see sk_diag_dump_icons(). */ |
| 168 | ++ U_LOCK_GC_LISTENER, /* used for listening socket while determining gc |
| 169 | ++ * candidates to close a small race window. |
| 170 | ++ */ |
| 171 | + }; |
| 172 | + |
| 173 | + static inline void unix_state_lock_nested(struct sock *sk, |
| 174 | +* Unmerged path net/unix/garbage.c |
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