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List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [syzbot] [btrfs?] INFO: task hung in __alloc_workqueue (2) To: Tejun Heo , Qu Wenruo Cc: syzbot , anna-maria@linutronix.de, clm@fb.com, dsterba@suse.com, frederic@kernel.org, josef@toxicpanda.com, linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, tglx@linutronix.de, jiangshanlai@gmail.com References: <6899154b.050a0220.51d73.0094.GAE@google.com> Content-Language: en-US From: Qu Wenruo Autocrypt: addr=quwenruo.btrfs@gmx.com; keydata= xsBNBFnVga8BCACyhFP3ExcTIuB73jDIBA/vSoYcTyysFQzPvez64TUSCv1SgXEByR7fju3o 8RfaWuHCnkkea5luuTZMqfgTXrun2dqNVYDNOV6RIVrc4YuG20yhC1epnV55fJCThqij0MRL 1NxPKXIlEdHvN0Kov3CtWA+R1iNN0RCeVun7rmOrrjBK573aWC5sgP7YsBOLK79H3tmUtz6b 9Imuj0ZyEsa76Xg9PX9Hn2myKj1hfWGS+5og9Va4hrwQC8ipjXik6NKR5GDV+hOZkktU81G5 gkQtGB9jOAYRs86QG/b7PtIlbd3+pppT0gaS+wvwMs8cuNG+Pu6KO1oC4jgdseFLu7NpABEB AAHNIlF1IFdlbnJ1byA8cXV3ZW5ydW8uYnRyZnNAZ214LmNvbT7CwJQEEwEIAD4CGwMFCwkI 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naECE4m4XiFc9RfCGhWgSygo2bX4cudif2OCHbYGp1WUL0AgtyTGiPUBb6hifobKHkyBSJkf7 +uRtgkWzHfNZmf7YUKqJ4CnmeIoVsOVy/xOBXk5uSKZ9dI+S99X6v8Mm5esSrQcqcb0wesUZY 8ErXZ+4Tj0PCUF0/xUZa2gdMJSYVWK7FNzmeofRWAQ0MiJuba6x3eMJgKqKr0CgWPumQHcFyd 7krwys8ec/FTfy1JoLuXiXgJQIJqwTYHhYPwaZ1D6a9GOmvzoj87vKQ2TYXhx7/VuMuHFV5YI 4HQb+YE86QWvY/yf29A7DinKh1rhxc90q0bAAGB/vbl2yJWd3z481xjFkclSkdWwME7s/klg3 V4shbAQuvJJ6qvN4pcdWnk2zutjvL10jtivtHlW0XjuZwJTDF5Uo93Q0OV6Q1q =E5=9C=A8 2025/8/12 03:45, Tejun Heo =E5=86=99=E9=81=93: > Hello, >=20 > On Mon, Aug 11, 2025 at 08:02:40AM +0930, Qu Wenruo wrote: > ... >>> Call Trace: >>> >>> context_switch kernel/sched/core.c:5357 [inline] >>> __schedule+0x16f3/0x4c20 kernel/sched/core.c:6961 >>> __schedule_loop kernel/sched/core.c:7043 [inline] >>> schedule+0x165/0x360 kernel/sched/core.c:7058 >>> schedule_timeout+0x9a/0x270 kernel/time/sleep_timeout.c:75 >>> do_wait_for_common kernel/sched/completion.c:100 [inline] >>> __wait_for_common kernel/sched/completion.c:121 [inline] >>> wait_for_common kernel/sched/completion.c:132 [inline] >>> wait_for_completion+0x2bf/0x5d0 kernel/sched/completion.c:153 >>> kthread_flush_worker+0x1c6/0x240 kernel/kthread.c:1563 >> >> This is flushing pwq_release_worker during error handling, and I didn't= see >> anything btrfs specific except btrfs is allocating an ordered workqueue >> which utilizes WQ_UNBOUND flag. >> >> And that WQ_UNBOUND flag is pretty widely used among other filesystems, >> maybe it's just btrfs have too many workqueues triggering this? >> >> Adding workqueue maintainers. >=20 > That flush stall likely is a secondary effect of another failure. The > kthread worker is already spun up and running and the work function > pwq_release_workfn() grabs several locks. Maybe someone else is stalling= on > those unless the kthread is somehow not allowed to run? Continued below. >=20 >>> Showing all locks held in the system: >>> 1 lock held by khungtaskd/38: >>> #0: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acqu= ire include/linux/rcupdate.h:331 [inline] >>> #0: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock= include/linux/rcupdate.h:841 [inline] >>> #0: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: debug_show_al= l_locks+0x2e/0x180 kernel/locking/lockdep.c:6775 >>> 1 lock held by udevd/5207: >>> #0: ffff8880358bfa18 (&ep->lock){++++}-{3:3}, at: write_lock_irq in= clude/linux/rwlock_rt.h:104 [inline] >>> #0: ffff8880358bfa18 (&ep->lock){++++}-{3:3}, at: ep_poll fs/eventp= oll.c:2127 [inline] >>> #0: ffff8880358bfa18 (&ep->lock){++++}-{3:3}, at: do_epoll_wait+0x8= 4d/0xbb0 fs/eventpoll.c:2560 >>> 2 locks held by getty/5598: >>> #0: ffff88823bfae8a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_r= ef_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243 >>> #1: ffffc90003e8b2e0 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_= tty_read+0x444/0x1410 drivers/tty/n_tty.c:2222 >>> 3 locks held by kworker/u8:3/5911: >>> 3 locks held by kworker/u8:7/5942: >>> 6 locks held by udevd/6060: >>> 1 lock held by udevd/6069: >>> 1 lock held by udevd/6190: >>> 6 locks held by udevd/6237: > ~~~trimmed~~~ >=20 > That's a lot of locks to be held, so something's not going right for sur= e. >=20 >>> Sending NMI from CPU 1 to CPUs 0: >>> NMI backtrace for cpu 0 >>> CPU: 0 UID: 0 PID: 5911 Comm: kworker/u8:3 Tainted: G W = 6.16.0-syzkaller-11852-g479058002c32 #0 PREEMPT_{RT,(full)} >>> Tainted: [W]=3DWARN >>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIO= S Google 07/12/2025 >>> Workqueue: bat_events batadv_iv_send_outstanding_bat_ogm_packet >>> RIP: 0010:get_timer_this_cpu_base kernel/time/timer.c:939 [inline] >>> RIP: 0010:__mod_timer+0x81c/0xf60 kernel/time/timer.c:1101 >>> Code: 01 00 00 00 48 8b 5c 24 20 41 0f b6 44 2d 00 84 c0 0f 85 72 06 0= 0 00 8b 2b e8 f0 bb 49 09 41 89 c5 89 c3 bf 08 00 00 00 89 c6 0f c1 1= 2 00 41 83 fd 07 44 89 34 24 0f 87 69 06 00 00 e8 4c bc >>> RSP: 0018:ffffc90004fff680 EFLAGS: 00000082 >>> RAX: 0000000000000000 RBX: 0000000000000000 RCX: f9fab87ca5ec6a00 >>> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000008 >>> RBP: 0000000000200000 R08: 0000000000000000 R09: 0000000000000000 >>> R10: dffffc0000000000 R11: fffff520009ffeac R12: ffff8880b8825a80 >>> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000802 >>> FS: 0000000000000000(0000) GS:ffff8881268cd000(0000) knlGS:0000000000= 000000 >>> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >>> CR2: 00007f46b6524000 CR3: 000000003afb2000 CR4: 00000000003526f0 >>> Call Trace: >>> >>> queue_delayed_work_on+0x18b/0x280 kernel/workqueue.c:2559 >>> queue_delayed_work include/linux/workqueue.h:684 [inline] >>> batadv_forw_packet_queue+0x239/0x2a0 net/batman-adv/send.c:691 >>> batadv_iv_ogm_schedule_buff net/batman-adv/bat_iv_ogm.c:842 [inline= ] >>> batadv_iv_ogm_schedule+0x892/0xf00 net/batman-adv/bat_iv_ogm.c:874 >>> batadv_iv_send_outstanding_bat_ogm_packet+0x6c6/0x7e0 net/batman-ad= v/bat_iv_ogm.c:1714 >>> process_one_work kernel/workqueue.c:3236 [inline] >>> process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3319 >>> worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400 >>> kthread+0x711/0x8a0 kernel/kthread.c:463 >>> ret_from_fork+0x3f9/0x770 arch/x86/kernel/process.c:148 >>> ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 >>> >=20 > So, task hung watchdog triggered and making all cpus dump their backtrac= es > and it's only one CPU. Is this a two CPU setup in a live lockup? I don't= see > anything apparent and these are time based conditions that can be trigge= red > by severely overloading the system too. If you can reproduce the conditi= ons, That's the problem, it looks like I'm either cursed or really unlucky, I= =20 have a very low chance of reproducibility of syzbot bugs. And it's the same failed-to-reproduce here. Thanks, Qu > seeing how the system is doing in general and whether the system can unw= ind > itself after killing the workload may be useful. >=20 > Thanks. >=20