next: suspicious RCU usage message since commit 'rcu: Remove superfluous versions of rcu_read_lock_sched_held()'

[Guenter Roeck <linux@roeck-us.net>]

Hi,

I see the following log message when running a qemu test for 'beagle'
with omap2plus_defconfig.

===============================
[ INFO: suspicious RCU usage. ]
4.6.0-rc4-next-20160422 #1 Not tainted
-------------------------------
include/trace/events/power.h:328 suspicious rcu_dereference_check() usage!

other info that might help us debug this:

RCU used illegally from idle CPU!
rcu_scheduler_active = 1, debug_locks = 0
RCU used illegally from extended quiescent state!
no locks held by swapper/0/0.

stack backtrace:
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.6.0-rc4-next-20160422 #1
Hardware name: Generic OMAP3-GP (Flattened Device Tree)
[<c010f55c>] (unwind_backtrace) from [<c010b64c>] (show_stack+0x10/0x14)
[<c010b64c>] (show_stack) from [<c047acbc>] (dump_stack+0xa8/0xe0)
[<c047acbc>] (dump_stack) from [<c012bc10>] (pwrdm_set_next_pwrst+0xf8/0x1cc)
[<c012bc10>] (pwrdm_set_next_pwrst) from [<c01269fc>] (omap3_enter_idle_bm+0x1b8/0x1e8)
[<c01269fc>] (omap3_enter_idle_bm) from [<c05fa0b8>] (cpuidle_enter_state+0x84/0x408)
[<c05fa0b8>] (cpuidle_enter_state) from [<c0182c1c>] (cpu_startup_entry+0x1c8/0x3f0)
[<c0182c1c>] (cpu_startup_entry) from [<c0b00c20>] (start_kernel+0x354/0x3cc)

bisect points to commit 'rcu: Remove superfluous versions of
rcu_read_lock_sched_held()'. Bisect log is attached.

Thanks,
Guenter

---
# bad: [73442f7becf1b305c966ad37f5991d030f8bc025] Add linux-next specific files for 20160422
# good: [c3b46c73264b03000d1e18b22f5caf63332547c9] Linux 4.6-rc4
git bisect start 'HEAD' 'v4.6-rc4'
# good: [f59d58f4c4c5d63b2f1768ab94465f9e98cd771d] Merge remote-tracking branch 'l2-mtd/master'
git bisect good f59d58f4c4c5d63b2f1768ab94465f9e98cd771d
# good: [ee634dd861741fa3112263c5fcd562e7953a8f3e] Merge remote-tracking branch 'tip/auto-latest'
git bisect good ee634dd861741fa3112263c5fcd562e7953a8f3e
# bad: [56ce28694cb53fb5609feca2735736583a35d5d1] Merge remote-tracking branch 'staging/staging-next'
git bisect bad 56ce28694cb53fb5609feca2735736583a35d5d1
# good: [9acc4500b44723d12bec63519038ef820479eaad] staging/lustre/llite: rename struct ccc_thread_info to vvp_thread_info
git bisect good 9acc4500b44723d12bec63519038ef820479eaad
# bad: [95585a7b8c5f8eac40402378bc7482376f17a3ff] Merge remote-tracking branch 'driver-core/driver-core-next'
git bisect bad 95585a7b8c5f8eac40402378bc7482376f17a3ff
# bad: [3052fd5d2b38b26deaa195aec34f18bacccdf40c] torture: Add starvation events to error summary
git bisect bad 3052fd5d2b38b26deaa195aec34f18bacccdf40c
# good: [a54062c0d95921d4fb0edc8d268021bf387e6c75] rcutorture: Add boot-time adjustment of leaf fanout
git bisect good a54062c0d95921d4fb0edc8d268021bf387e6c75
# bad: [dcd36d01fb3f99d1d5df01714f6ccbe3fbbaf81f] Merge branches 'doc.2016.04.19a', 'exp.2016.03.31d', 'fixes.2016.03.31d' and 'torture.2016.04.21a' into HEAD
git bisect bad dcd36d01fb3f99d1d5df01714f6ccbe3fbbaf81f
# good: [3b5f668e715bc19610ad967ef97a7e8c55a186ec] rcu: Overlap wakeups with next expedited grace period
git bisect good 3b5f668e715bc19610ad967ef97a7e8c55a186ec
# good: [5413e24c943da33306047fc091fa34fa4f261b3b] documentation: Sharpen up the no-readers quick quiz
git bisect good 5413e24c943da33306047fc091fa34fa4f261b3b
# bad: [293e2421fe25839500207eda123cc4475f8d17b8] rcu: Remove superfluous versions of rcu_read_lock_sched_held()
git bisect bad 293e2421fe25839500207eda123cc4475f8d17b8
# good: [fcfd0a237bfcf0c314005007e9d76e55a25e2bad] rcu: Make FQS schedule advance only if FQS happened
git bisect good fcfd0a237bfcf0c314005007e9d76e55a25e2bad
# good: [8c7c4829a81c1838f18c12ce5a3a5c29a08bf0a8] rcu: Awaken grace-period kthread if too long since FQS
git bisect good 8c7c4829a81c1838f18c12ce5a3a5c29a08bf0a8
# first bad commit: [293e2421fe25839500207eda123cc4475f8d17b8] rcu: Remove superfluous versions of rcu_read_lock_sched_held()