[syzbot] [net?] INFO: task hung in unix_stream_sendmsg

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 71b605d32017 net: phy: aquantia: add AQR113 PHY ID
git tree: net-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=1107270c180000
kernel config: https://syzkaller.appspot.com/x/.config?x=970c7b6c80a096da
dashboard link: https://syzkaller.appspot.com/bug?extid=ecab4d36f920c3574bf9
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=14a0522c180000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1557b752180000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/4e43093a84c4/disk-71b605d3.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/f0cccd84c6e5/vmlinux-71b605d3.xz
kernel image: https://storage.googleapis.com/syzbot-assets/581c58b8f080/bzImage-71b605d3.xz

The issue was bisected to:

commit 25236c91b5ab4a26a56ba2e79b8060cf4e047839
Author: Kuniyuki Iwashima <kun...@amazon.com>
Date: Fri Feb 9 22:04:53 2024 +0000

af_unix: Fix task hung while purging oob_skb in GC.

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=177f209c180000
final oops: https://syzkaller.appspot.com/x/report.txt?x=14ff209c180000
console output: https://syzkaller.appspot.com/x/log.txt?x=10ff209c180000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ecab4d...@syzkaller.appspotmail.com
Fixes: 25236c91b5ab ("af_unix: Fix task hung while purging oob_skb in GC.")

INFO: task syz-executor397:5487 blocked for more than 143 seconds.
Not tainted 6.8.0-rc4-syzkaller-01028-g71b605d32017 #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor397 state:D stack:26800 pid:5487 tgid:5487 ppid:5066 flags:0x00004006
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5400 [inline]
__schedule+0x17d1/0x49f0 kernel/sched/core.c:6727
__schedule_loop kernel/sched/core.c:6802 [inline]
schedule+0x149/0x260 kernel/sched/core.c:6817
schedule_timeout+0xb0/0x310 kernel/time/timer.c:2159
do_wait_for_common kernel/sched/completion.c:95 [inline]
__wait_for_common kernel/sched/completion.c:116 [inline]
wait_for_common kernel/sched/completion.c:127 [inline]
wait_for_completion+0x354/0x620 kernel/sched/completion.c:148
__flush_work+0x950/0xad0 kernel/workqueue.c:3410
unix_stream_sendmsg+0x1c3/0xe60 net/unix/af_unix.c:2264
sock_sendmsg_nosec net/socket.c:730 [inline]
__sock_sendmsg+0x221/0x270 net/socket.c:745
____sys_sendmsg+0x525/0x7d0 net/socket.c:2584
___sys_sendmsg net/socket.c:2638 [inline]
__sys_sendmsg+0x2b0/0x3a0 net/socket.c:2667
do_syscall_64+0xf9/0x240
entry_SYSCALL_64_after_hwframe+0x6f/0x77
RIP: 0033:0x7f4cfb950b39
RSP: 002b:00007ffd1e7e2758 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f4cfb950b39
RDX: 0000000000008001 RSI: 00000000200015c0 RDI: 0000000000000004
RBP: 000000000001bf72 R08: 0000000000000006 R09: 0000000000000006
R10: 0000000000000006 R11: 0000000000000246 R12: 00007ffd1e7e276c
R13: 431bde82d7b634db R14: 0000000000000001 R15: 0000000000000001
</TASK>

Showing all locks held in the system:
1 lock held by khungtaskd/29:
#0: ffffffff8e130ae0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:298 [inline]
#0: ffffffff8e130ae0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:750 [inline]
#0: ffffffff8e130ae0 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x55/0x2a0 kernel/locking/lockdep.c:6614
2 locks held by kworker/u4:8/2784:
1 lock held by syslogd/4503:
#0: ffff8880b953c958 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested+0x2a/0x140 kernel/sched/core.c:559
2 locks held by getty/4822:
#0: ffff8880304f90a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
#1: ffffc90002efe2f0 (&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0x6b4/0x1e10 drivers/tty/n_tty.c:2201

=============================================

NMI backtrace for cpu 0
CPU: 0 PID: 29 Comm: khungtaskd Not tainted 6.8.0-rc4-syzkaller-01028-g71b605d32017 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x1e7/0x2e0 lib/dump_stack.c:106
nmi_cpu_backtrace+0x49c/0x4d0 lib/nmi_backtrace.c:113
nmi_trigger_cpumask_backtrace+0x198/0x320 lib/nmi_backtrace.c:62
trigger_all_cpu_backtrace include/linux/nmi.h:160 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:222 [inline]
watchdog+0xfaf/0xff0 kernel/hung_task.c:379
kthread+0x2ef/0x390 kernel/kthread.c:388
ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1b/0x30 arch/x86/entry/entry_64.S:242
</TASK>
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 2784 Comm: kworker/u4:8 Not tainted 6.8.0-rc4-syzkaller-01028-g71b605d32017 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
Workqueue: events_unbound __unix_gc
RIP: 0010:__sanitizer_cov_trace_pc+0x0/0x70 kernel/kcov.c:200
Code: 89 fb e8 23 00 00 00 48 8b 3d 84 f5 1a 0c 48 89 de 5b e9 43 26 57 00 0f 1f 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 <f3> 0f 1e fa 48 8b 04 24 65 48 8b 0d 90 52 70 7e 65 8b 15 91 52 70
RSP: 0018:ffffc9000a17fa78 EFLAGS: 00000287
RAX: ffffffff8a0a6108 RBX: ffff88802b6c2640 RCX: ffff88802c0b3b80
RDX: 0000000000000000 RSI: 0000000000000002 RDI: 0000000000000000
RBP: ffffc9000a17fbf0 R08: ffffffff89383f1d R09: 1ffff1100ee5ff84
R10: dffffc0000000000 R11: ffffed100ee5ff85 R12: 1ffff110056d84ee
R13: ffffc9000a17fae0 R14: 0000000000000000 R15: ffffffff8f47b840
FS: 0000000000000000(0000) GS:ffff8880b9500000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffef5687ff8 CR3: 0000000029b34000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<NMI>
</NMI>
<TASK>
__unix_gc+0xe69/0xf40 net/unix/garbage.c:343
process_one_work kernel/workqueue.c:2633 [inline]
process_scheduled_works+0x913/0x1420 kernel/workqueue.c:2706
worker_thread+0xa5f/0x1000 kernel/workqueue.c:2787
kthread+0x2ef/0x390 kernel/kthread.c:388
ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1b/0x30 arch/x86/entry/entry_64.S:242
</TASK>
INFO: NMI handler (nmi_cpu_backtrace_handler) took too long to run: 1.061 msecs


---
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For information about bisection process see: https://goo.gl/tpsmEJ#bisection

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
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If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

[Kuniyuki Iwashima]

From: syzbot <syzbot+ecab4d...@syzkaller.appspotmail.com>
Date: Sun, 18 Feb 2024 00:09:19 -0800

#syz test git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git 25236c91b5ab4a26a56ba2e79b8060cf4e047839

diff --git a/net/unix/garbage.c b/net/unix/garbage.c
index 51acf795f096..3b345b7a228b 100644
--- a/net/unix/garbage.c
+++ b/net/unix/garbage.c
@@ -340,13 +340,18 @@ static void __unix_gc(struct work_struct *work)
__skb_queue_purge(&hitlist);

#if IS_ENABLED(CONFIG_AF_UNIX_OOB)
- while (!list_empty(&gc_candidates)) {
- u = list_entry(gc_candidates.next, struct unix_sock, link);
+ u = list_first_entry_or_null(&gc_candidates, struct unix_sock, link);
+
+ while (u) {
if (u->oob_skb) {
struct sk_buff *skb = u->oob_skb;

u->oob_skb = NULL;
kfree_skb(skb);
+
+ u = list_first_entry_or_null(&gc_candidates, struct unix_sock, link);
+ } else {
+ u = list_next_entry(u, link);
}
}
#endif

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-and-tested-by: syzbot+ecab4d...@syzkaller.appspotmail.com

Tested on:

commit: 25236c91 af_unix: Fix task hung while purging oob_skb ..
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git
console output: https://syzkaller.appspot.com/x/log.txt?x=151b970c180000
kernel config: https://syzkaller.appspot.com/x/.config?x=c368c5806a3ee9fc

dashboard link: https://syzkaller.appspot.com/bug?extid=ecab4d36f920c3574bf9
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

patch: https://syzkaller.appspot.com/x/patch.diff?x=13ecdffc180000

Note: testing is done by a robot and is best-effort only.

[Kuniyuki Iwashima]

From: syzbot <syzbot+ecab4d...@syzkaller.appspotmail.com>
Date: Sun, 18 Feb 2024 00:09:19 -0800

#syz test git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git 25236c91b5ab4a26a56ba2e79b8060cf4e047839

diff --git a/net/unix/garbage.c b/net/unix/garbage.c

index 51acf795f096..fa39b6265238 100644
--- a/net/unix/garbage.c
+++ b/net/unix/garbage.c
@@ -322,9 +322,17 @@ static void __unix_gc(struct work_struct *work)
* which are creating the cycle(s).
*/
skb_queue_head_init(&hitlist);
- list_for_each_entry(u, &gc_candidates, link)
+ list_for_each_entry(u, &gc_candidates, link) {
scan_children(&u->sk, inc_inflight, &hitlist);

+#if IS_ENABLED(CONFIG_AF_UNIX_OOB)
+ if (u->oob_skb) {
+ kfree_skb(u->oob_skb);
+ u->oob_skb = NULL;
+ }
+#endif
+ }
+
/* not_cycle_list contains those sockets which do not make up a
* cycle. Restore these to the inflight list.
*/
@@ -339,18 +347,6 @@ static void __unix_gc(struct work_struct *work)
/* Here we are. Hitlist is filled. Die. */
__skb_queue_purge(&hitlist);

-#if IS_ENABLED(CONFIG_AF_UNIX_OOB)

- while (!list_empty(&gc_candidates)) {
- u = list_entry(gc_candidates.next, struct unix_sock, link);

- if (u->oob_skb) {
- struct sk_buff *skb = u->oob_skb;
-
- u->oob_skb = NULL;
- kfree_skb(skb);
- }
- }
-#endif
-
spin_lock(&unix_gc_lock);

/* All candidates should have been detached by now. */

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-and-tested-by: syzbot+ecab4d...@syzkaller.appspotmail.com

Tested on:

commit: 25236c91 af_unix: Fix task hung while purging oob_skb ..
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git

console output: https://syzkaller.appspot.com/x/log.txt?x=171f722c180000
kernel config: https://syzkaller.appspot.com/x/.config?x=c368c5806a3ee9fc

dashboard link: https://syzkaller.appspot.com/bug?extid=ecab4d36f920c3574bf9
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

patch: https://syzkaller.appspot.com/x/patch.diff?x=12e5c872180000