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SubjectWARNING: suspicious RCU usage since next-20220304
Hello

Booting my sun8i-a83t-bananapi-m3 since next-20220304 lead to lot of RCU warning:
[ 0.000000] CPU: PIPT / VIPT nonaliasing data cache, VIPT aliasing instruction cache
[ 0.000000] OF: fdt: Machine model: Banana Pi BPI-M3
[ 0.000000] earlycon: uart0 at MMIO32 0x01c28000 (options '')
[ 0.000000] printk: bootconsole [uart0] enabled
[ 0.000000] Memory policy: Data cache writealloc
[ 0.000000] cma: Reserved 16 MiB at 0xbf000000
[ 0.000000] Zone ranges:
[ 0.000000] Normal [mem 0x0000000040000000-0x000000006fffffff]
[ 0.000000] HighMem [mem 0x0000000070000000-0x00000000bfffffff]
[ 0.000000] Movable zone start for each node
[ 0.000000] Early memory node ranges
[ 0.000000] node 0: [mem 0x0000000040000000-0x00000000bfffffff]
[ 0.000000] Initmem setup node 0 [mem 0x0000000040000000-0x00000000bfffffff]
[ 0.000000] percpu: Embedded 16 pages/cpu s34740 r8192 d22604 u65536
[ 0.000000] Built 1 zonelists, mobility grouping on. Total pages: 522752
[ 0.000000] Kernel command line: console=ttyS0,115200n8 root=/dev/ram0 earlycon=uart,mmio32,0x01c28000 ip=dhcp
[ 0.000000] Dentry cache hash table entries: 131072 (order: 7, 524288 bytes, linear)
[ 0.000000] Inode-cache hash table entries: 65536 (order: 6, 262144 bytes, linear)
[ 0.000000] mem auto-init: stack:off, heap alloc:off, heap free:off
[ 0.000000] Memory: 2017876K/2097152K available (8192K kernel code, 1395K rwdata, 2956K rodata, 1024K init, 7184K bss, 62892K reserved, 16384K cma-reserved, 1294336K highmem)
[ 0.000000] SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=8, Nodes=1
[ 0.000000] trace event string verifier disabled
[ 0.000000] Running RCU self tests
[ 0.000000] rcu: Hierarchical RCU implementation.
[ 0.000000] rcu: RCU event tracing is enabled.
[ 0.000000] rcu: RCU lockdep checking is enabled.
[ 0.000000] rcu: RCU calculated value of scheduler-enlistment delay is 10 jiffies.
[ 0.000000] NR_IRQS: 16, nr_irqs: 16, preallocated irqs: 16
[ 0.000000] rcu: srcu_init: Setting srcu_struct sizes based on contention.
[ 0.000000] random: get_random_bytes called from start_kernel+0x534/0x6cc with crng_init=0
[ 0.000000] arch_timer: cp15 timer(s) running at 24.00MHz (virt).
[ 0.000000] clocksource: arch_sys_counter: mask: 0xffffffffffffff max_cycles: 0x588fe9dc0, max_idle_ns: 440795202592 ns
[ 0.000003] sched_clock: 56 bits at 24MHz, resolution 41ns, wraps every 4398046511097ns
[ 0.008649] Switching to timer-based delay loop, resolution 41ns
[ 0.015608] clocksource: timer: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 79635851949 ns
[ 0.026505] Console: colour dummy device 80x30
[ 0.031367] Lock dependency validator: Copyright (c) 2006 Red Hat, Inc., Ingo Molnar
[ 0.039759] ... MAX_LOCKDEP_SUBCLASSES: 8
[ 0.044185] ... MAX_LOCK_DEPTH: 48
[ 0.048693] ... MAX_LOCKDEP_KEYS: 8192
[ 0.053417] ... CLASSHASH_SIZE: 4096
[ 0.058117] ... MAX_LOCKDEP_ENTRIES: 32768
[ 0.062911] ... MAX_LOCKDEP_CHAINS: 65536
[ 0.067721] ... CHAINHASH_SIZE: 32768
[ 0.072516] memory used by lock dependency info: 4061 kB
[ 0.078364] memory used for stack traces: 2112 kB
[ 0.083533] per task-struct memory footprint: 1536 bytes
[ 0.089482] Calibrating delay loop (skipped), value calculated using timer frequency.. 48.00 BogoMIPS (lpj=240000)
[ 0.100709] pid_max: default: 32768 minimum: 301
[ 0.106465] Mount-cache hash table entries: 2048 (order: 1, 8192 bytes, linear)
[ 0.114435] Mountpoint-cache hash table entries: 2048 (order: 1, 8192 bytes, linear)
[ 0.125719] CPU: Testing write buffer coherency: ok
[ 0.132334]
[ 0.134009] =============================
[ 0.138348] WARNING: suspicious RCU usage
[ 0.142679] 5.17.0-rc6-next-20220307-00130-g074e6e0284df-dirty #222 Not tainted
[ 0.150565] -----------------------------
[ 0.154901] include/linux/cgroup.h:481 suspicious rcu_dereference_check() usage!
[ 0.162883]
[ 0.162883] other info that might help us debug this:
[ 0.162883]
[ 0.171509]
[ 0.171509] rcu_scheduler_active = 1, debug_locks = 1
[ 0.178546] 2 locks held by kthreadd/2:
[ 0.182694] #0: c19216b4 (&p->pi_lock){....}-{2:2}, at: task_rq_lock+0x34/0x134
[ 0.190763] #1: eef68b50 (&rq->__lock){-...}-{2:2}, at: task_rq_lock+0x5c/0x134
[ 0.198810]
[ 0.198810] stack backtrace:
[ 0.203522] CPU: 0 PID: 2 Comm: kthreadd Not tainted 5.17.0-rc6-next-20220307-00130-g074e6e0284df-dirty #222
[ 0.214132] Hardware name: Allwinner A83t board
[ 0.219031] unwind_backtrace from show_stack+0x10/0x14
[ 0.224690] show_stack from 0xf0835e8c
[ 0.228933]
[ 0.230564] =============================
[ 0.234891] WARNING: suspicious RCU usage
[ 0.239217] 5.17.0-rc6-next-20220307-00130-g074e6e0284df-dirty #222 Not tainted
[ 0.247108] -----------------------------
[ 0.251433] include/linux/cgroup.h:481 suspicious rcu_dereference_check() usage!
[ 0.259419]
[ 0.259419] other info that might help us debug this:
[ 0.259419]
[ 0.268061]
[ 0.268061] rcu_scheduler_active = 1, debug_locks = 1
[ 0.275103] no locks held by kthreadd/2.
[ 0.279336]
[ 0.279336] stack backtrace:
[ 0.284043] CPU: 0 PID: 2 Comm: kthreadd Not tainted 5.17.0-rc6-next-20220307-00130-g074e6e0284df-dirty #222
[ 0.294643] Hardware name: Allwinner A83t board
[ 0.299534] unwind_backtrace from show_stack+0x10/0x14
[ 0.305193] show_stack from 0xf0801efc
[ 0.309508] /cpus/cpu@0 missing clock-frequency property
[ 0.315324] /cpus/cpu@1 missing clock-frequency property
[ 0.321178] /cpus/cpu@2 missing clock-frequency property
[ 0.326983] /cpus/cpu@3 missing clock-frequency property
[ 0.332833] /cpus/cpu@100 missing clock-frequency property
[ 0.338835] /cpus/cpu@101 missing clock-frequency property
[ 0.344897] /cpus/cpu@102 missing clock-frequency property
[ 0.350930] /cpus/cpu@103 missing clock-frequency property
[ 0.356920] CPU0: thread -1, cpu 0, socket 0, mpidr 80000000
[ 0.366264] Setting up static identity map for 0x40100000 - 0x40100060
[ 0.374286] ARM CCI driver probed
[ 0.378726] sunxi multi cluster SMP support installed
[ 0.385497] rcu: Hierarchical SRCU implementation.
[ 0.391811]
[ 0.393463] =============================
[ 0.397800] WARNING: suspicious RCU usage
[ 0.402138] 5.17.0-rc6-next-20220307-00130-g074e6e0284df-dirty #222 Not tainted
[ 0.410033] -----------------------------
[ 0.414358] include/linux/cgroup.h:481 suspicious rcu_dereference_check() usage!
[ 0.422337]
[ 0.422337] other info that might help us debug this:
[ 0.422337]
[ 0.430972]
[ 0.430972] rcu_scheduler_active = 1, debug_locks = 1
[ 0.438016] 1 lock held by migration/0/12:
[ 0.442441] #0: eef68b50 (&rq->__lock){-...}-{2:2}, at: __schedule+0xf4/0xaa4
[ 0.450325]
[ 0.450325] stack backtrace:
[ 0.455037] CPU: 0 PID: 12 Comm: migration/0 Not tainted 5.17.0-rc6-next-20220307-00130-g074e6e0284df-dirty #222
[ 0.466027] Hardware name: Allwinner A83t board
[ 0.470920] Stopper: 0x0 <- 0x0
[ 0.474328] unwind_backtrace from show_stack+0x10/0x14
[ 0.479980] show_stack from 0xf087debc

I bisect it to dc6e0818bc9a0336d9accf3ea35d146d72aa7a18 sched/cpuacct: Optimize away RCU read lock
reverting this commit removed some RCU but the boot is clean since I reverted also 3eba0505d03a9c1eb30d40c2330c0880b22d1b3a "sched/cpuacct: Remove redundant RCU read lock"

Regards

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