[powerpc][5.13.0-rc7] Kernel warning (kernel/sched/fair.c:401) while running LTP tests

[Sachin Sant]

While running LTP tests (cfs_bandwidth01) against 5.13.0-rc7 kernel on a powerpc box
following warning is seen

[ 6611.331827] ------------[ cut here ]------------
[ 6611.331855] rq->tmp_alone_branch != &rq->leaf_cfs_rq_list
[ 6611.331862] WARNING: CPU: 8 PID: 0 at kernel/sched/fair.c:401 unthrottle_cfs_rq+0x4cc/0x590
[ 6611.331883] Modules linked in: nfsv3 nfs_acl nfs lockd grace fscache netfs tun brd overlay vfat fat btrfs blake2b_generic xor zstd_compress raid6_pq xfs loop sctp ip6_udp_tunnel udp_tunnel libcrc32c dm_mod bonding rfkill sunrpc pseries_rng xts vmx_crypto sch_fq_codel ip_tables ext4 mbcache jbd2 sd_mod t10_pi sg ibmvscsi ibmveth scsi_transport_srp fuse [last unloaded: init_module]
[ 6611.331957] CPU: 8 PID: 0 Comm: swapper/8 Tainted: G           OE     5.13.0-rc6-gcba5e97280f5 #1
[ 6611.331968] NIP:  c0000000001b7aac LR: c0000000001b7aa8 CTR: c000000000722d30
[ 6611.331976] REGS: c00000000274f3a0 TRAP: 0700   Tainted: G           OE      (5.13.0-rc6-gcba5e97280f5)
[ 6611.331985] MSR:  8000000000029033 <SF,EE,ME,IR,DR,RI,LE>  CR: 48000224  XER: 00000005
[ 6611.332002] CFAR: c00000000014ca20 IRQMASK: 1 
[ 6611.332002] GPR00: c0000000001b7aa8 c00000000274f640 c000000001abaf00 000000000000002d 
[ 6611.332002] GPR04: 00000000ffff7fff c00000000274f300 0000000000000027 c000000efdb07e08 
[ 6611.332002] GPR08: 0000000000000023 0000000000000001 0000000000000027 c000000001976680 
[ 6611.332002] GPR12: 0000000000000000 c000000effc0be80 c000000ef07b3f90 000000001eefe200 
[ 6611.332002] GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 
[ 6611.332002] GPR20: 0000000000000001 c000000000fa6c08 c000000000fa6030 0000000000000001 
[ 6611.332002] GPR24: 0000000000000000 0000000000000000 c000000efde12380 0000000000000001 
[ 6611.332002] GPR28: 0000000000000001 0000000000000000 c000000efde12400 0000000000000000 
[ 6611.332094] NIP [c0000000001b7aac] unthrottle_cfs_rq+0x4cc/0x590
[ 6611.332104] LR [c0000000001b7aa8] unthrottle_cfs_rq+0x4c8/0x590
[ 6611.332113] Call Trace:
[ 6611.332116] [c00000000274f640] [c0000000001b7aa8] unthrottle_cfs_rq+0x4c8/0x590 (unreliable)
[ 6611.332128] [c00000000274f6e0] [c0000000001b7e38] distribute_cfs_runtime+0x1d8/0x280
[ 6611.332139] [c00000000274f7b0] [c0000000001b81d0] sched_cfs_period_timer+0x140/0x330
[ 6611.332149] [c00000000274f870] [c00000000022a03c] __hrtimer_run_queues+0x17c/0x380
[ 6611.332158] [c00000000274f8f0] [c00000000022ac68] hrtimer_interrupt+0x128/0x2f0
[ 6611.332168] [c00000000274f9a0] [c00000000002940c] timer_interrupt+0x13c/0x370
[ 6611.332179] [c00000000274fa00] [c000000000009c04] decrementer_common_virt+0x1a4/0x1b0
[ 6611.332189] --- interrupt: 900 at plpar_hcall_norets_notrace+0x18/0x24
[ 6611.332199] NIP:  c0000000000f6af8 LR: c000000000a05f68 CTR: 0000000000000000
[ 6611.332206] REGS: c00000000274fa70 TRAP: 0900   Tainted: G           OE      (5.13.0-rc6-gcba5e97280f5)
[ 6611.332214] MSR:  800000000280b033 <SF,VEC,VSX,EE,FP,ME,IR,DR,RI,LE>  CR: 28000224  XER: 00000000
[ 6611.332234] CFAR: 0000000000000c00 IRQMASK: 0 
[ 6611.332234] GPR00: 0000000000000000 c00000000274fd10 c000000001abaf00 0000000000000000 
[ 6611.332234] GPR04: 00000000000000c0 0000000000000080 0001a91c68b80fa1 00000000000003dc 
[ 6611.332234] GPR08: 000000000001f400 0000000000000001 0000000000000000 0000000000000000 
[ 6611.332234] GPR12: 0000000000000000 c000000effc0be80 c000000ef07b3f90 000000001eefe200 
[ 6611.332234] GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 
[ 6611.332234] GPR20: 0000000000000001 0000000000000002 0000000000000010 c0000000019fe2f8 
[ 6611.332234] GPR24: 0000000000000001 00000603517d757e 0000000000000000 0000000000000000 
[ 6611.332234] GPR28: 0000000000000001 0000000000000000 c000000001231f90 c000000001231f98 
[ 6611.332323] NIP [c0000000000f6af8] plpar_hcall_norets_notrace+0x18/0x24
[ 6611.332332] LR [c000000000a05f68] check_and_cede_processor+0x48/0x60
[ 6611.332340] --- interrupt: 900
[ 6611.332345] [c00000000274fd10] [c000000efdb92380] 0xc000000efdb92380 (unreliable)
[ 6611.332355] [c00000000274fd70] [c000000000a063bc] dedicated_cede_loop+0x9c/0x1b0
[ 6611.332364] [c00000000274fdc0] [c000000000a02b04] cpuidle_enter_state+0x2e4/0x4e0
[ 6611.332375] [c00000000274fe20] [c000000000a02da0] cpuidle_enter+0x50/0x70
[ 6611.332385] [c00000000274fe60] [c0000000001a883c] call_cpuidle+0x4c/0x80
[ 6611.332393] [c00000000274fe80] [c0000000001a8ee0] do_idle+0x380/0x3e0
[ 6611.332402] [c00000000274ff00] [c0000000001a91bc] cpu_startup_entry+0x3c/0x40
[ 6611.332411] [c00000000274ff30] [c000000000063ff8] start_secondary+0x298/0x2b0
[ 6611.332421] [c00000000274ff90] [c00000000000c754] start_secondary_prolog+0x10/0x14
[ 6611.332430] Instruction dump:
[ 6611.332435] 4bfffc44 3d22fff6 8929f328 2f890000 409efea4 39200001 3d42fff6 3c62ff4f 
[ 6611.332451] 3863bcd8 992af328 4bf94f15 60000000 <0fe00000> 4bfffe80 7f6407b4 7f43d378 
[ 6611.332466] ---[ end trace 1346f865cd1cae91 ]—

5.13.0-rc6 was good. Bisect points to following patch

commit a7b359fc6a37
sched/fair: Correctly insert cfs_rq's to list on unthrottle

The test runs to completion(without this warning) if the patch is reverted.

Thanks
-Sachin