The commit 68f83057 ("workqueue: Reap workers via kthread_stop()
and remove detach_completion") changes the procedure of destroying
workers; the dying workers are kept in the cull_list in wake_dying_workers()
with the pool lock held and removed from the cull_list by the newly
added reap_dying_workers() without the pool lock.

This can cause a warning if the dying worker is wokenup earlier than
reaped as reported by Marc:

2024/07/23 18:01:21 [M83LP63]: [  157.267727] ------------[ cut here ]------------
2024/07/23 18:01:21 [M83LP63]: [  157.267735] WARNING: CPU: 21 PID: 725 at kernel/workqueue.c:3340 worker_thread+0x54e/0x558
2024/07/23 18:01:21 [M83LP63]: [  157.267746] Modules linked in: binfmt_misc nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct nft_chain_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 ip_set nf_tables sunrpc dm_service_time s390_trng vfio_ccw mdev vfio_iommu_type1 vfio sch_fq_codel
2024/07/23 18:01:21 [M83LP63]: loop dm_multipath configfs nfnetlink lcs ctcm fsm zfcp scsi_transport_fc ghash_s390 prng chacha_s390 libchacha aes_s390 des_s390 libdes sha3_512_s390 sha3_256_s390 sha512_s390 sha256_s390 sha1_s390 sha_common scm_block eadm_sch scsi_dh_rdac scsi_dh_emc scsi_dh_alua pkey zcrypt rng_core autofs4
2024/07/23 18:01:21 [M83LP63]: [  157.267792] CPU: 21 PID: 725 Comm: kworker/dying Not tainted 6.10.0-rc2-00239-g68f83057 #95
2024/07/23 18:01:21 [M83LP63]: [  157.267796] Hardware name: IBM 3906 M04 704 (LPAR)
2024/07/23 18:01:21 [M83LP63]: [  157.267802]            R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:1 PM:0 RI:0 EA:3
2024/07/23 18:01:21 [M83LP63]: [  157.267797] Krnl PSW : 0704d00180000000 000003d600fcd9fa (worker_thread+0x552/0x558)
2024/07/23 18:01:21 [M83LP63]: [  157.267806] Krnl GPRS: 6479696e6700776f 000002c901b62780 000003d602493ec8 000002c914954600
2024/07/23 18:01:21 [M83LP63]: [  157.267809]            0000000000000000 0000000000000008 000002c901a85400 000002c90719e840
2024/07/23 18:01:21 [M83LP63]: [  157.267811]            000002c90719e880 000002c901a85420 000002c91127adf0 000002c901a85400
2024/07/23 18:01:21 [M83LP63]: [  157.267813]            000002c914954600 0000000000000000 000003d600fcd772 000003560452bd98
2024/07/23 18:01:21 [M83LP63]: [  157.267822] Krnl Code: 000003d600fcd9ec: c0e500674262        brasl   %r14,000003d601cb5eb0
2024/07/23 18:01:21 [M83LP63]: [  157.267822]            000003d600fcd9f2: a7f4ffc8            brc     15,000003d600fcd982
2024/07/23 18:01:21 [M83LP63]: [  157.267822]           #000003d600fcd9f6: af000000            mc      0,0
2024/07/23 18:01:21 [M83LP63]: [  157.267822]           >000003d600fcd9fa: a7f4fec2            brc     15,000003d600fcd77e
2024/07/23 18:01:21 [M83LP63]: [  157.267822]            000003d600fcd9fe: 0707                bcr     0,%r7
2024/07/23 18:01:21 [M83LP63]: [  157.267822]            000003d600fcda00: c00400682e10        brcl    0,000003d601cd3620
2024/07/23 18:01:21 [M83LP63]: [  157.267822]            000003d600fcda06: eb7ff0500024        stmg    %r7,%r15,80(%r15)
2024/07/23 18:01:21 [M83LP63]: [  157.267822]            000003d600fcda0c: b90400ef            lgr     %r14,%r15
2024/07/23 18:01:21 [M83LP63]: [  157.267853] Call Trace:
2024/07/23 18:01:21 [M83LP63]: [  157.267855]  [<000003d600fcd9fa>] worker_thread+0x552/0x558
2024/07/23 18:01:21 [M83LP63]: [  157.267859] ([<000003d600fcd772>] worker_thread+0x2ca/0x558)
2024/07/23 18:01:21 [M83LP63]: [  157.267862]  [<000003d600fd6c80>] kthread+0x120/0x128
2024/07/23 18:01:21 [M83LP63]: [  157.267865]  [<000003d600f5305c>] __ret_from_fork+0x3c/0x58
2024/07/23 18:01:21 [M83LP63]: [  157.267868]  [<000003d601cc746a>] ret_from_fork+0xa/0x30
2024/07/23 18:01:21 [M83LP63]: [  157.267873] Last Breaking-Event-Address:
2024/07/23 18:01:21 [M83LP63]: [  157.267874]  [<000003d600fcd778>] worker_thread+0x2d0/0x558

Since the procedure of destroying workers is changed, the WARN_ON_ONCE()
becomes incorrect and should be removed.

Cc: Marc Hartmayer <mhartmay@linux.ibm.com>
Link: https://lore.kernel.org/lkml/87le1sjd2e.fsf@linux.ibm.com/Reported-by: Marc Hartmayer <mhartmay@linux.ibm.com>
Fixes: 68f83057 ("workqueue: Reap workers via kthread_stop() and remove detach_completion")
Cc: stable@vger.kernel.org # v6.11+
Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Signed-off-by: Tejun Heo <tj@kernel.org>