Suspicious RCU usage at boot w/ arm ipi trace events?

[John Stultz]

Not sure if I have the right folks on CC. Noticed this booting on a
apq8064 based system w/ 4.1-rc7 (plus a few patches that I believe are
unrelated).


[    0.008796] CPU0: thread -1, cpu 0, socket 0, mpidr 80000000
[    0.009024] Setting up static identity map for 0x80208280 - 0x802082d8
[    0.084781] CPU1: thread -1, cpu 1, socket 0, mpidr 80000001
[    0.085119]
[    0.085139] ===============================
[    0.085152] [ INFO: suspicious RCU usage. ]
[    0.085168] 4.1.0-rc7-00033-gb5bed2f #153 Not tainted
[    0.085180] -------------------------------
[    0.085195] include/trace/events/ipi.h:68 suspicious
rcu_dereference_check() usage!
[    0.085205]
[    0.085205] other info that might help us debug this:
[    0.085205]
[    0.085220]
[    0.085220] RCU used illegally from idle CPU!
[    0.085220] rcu_scheduler_active = 1, debug_locks = 0
[    0.085235] RCU used illegally from extended quiescent state!
[    0.085247] no locks held by swapper/0/0.
[    0.085256]
[    0.085256] stack backtrace:
[    0.085275] CPU: 0 PID: 0 Comm: swapper/0 Not tainted
4.1.0-rc7-00033-gb5bed2f #153
[    0.085288] Hardware name: Qualcomm (Flattened Device Tree)
[    0.085323] [<c0216b08>] (unwind_backtrace) from [<c02136e8>]
(show_stack+0x10/0x14)
[    0.085348] [<c02136e8>] (show_stack) from [<c075e678>]
(dump_stack+0x70/0xbc)
[    0.085369] [<c075e678>] (dump_stack) from [<c0215a80>]
(handle_IPI+0x428/0x604)
[    0.085393] [<c0215a80>] (handle_IPI) from [<c020942c>]
(gic_handle_irq+0x54/0x5c)
[    0.085423] [<c020942c>] (gic_handle_irq) from [<c0766604>]
(__irq_svc+0x44/0x7c)
[    0.085436] Exception stack(0xc09f3f48 to 0xc09f3f90)
[    0.085451] 3f40:                   00000001 00000001 00000000
c09f73b8 c09f4528 c0a5de9c
[    0.085468] 3f60: c076b4f0 00000000 00000000 c09ef108 c0a5cec1
00000001 00000000 c09f3f90
[    0.085481] 3f80: c026bf60 c0210ab8 20000113 ffffffff
[    0.085512] [<c0766604>] (__irq_svc) from [<c0210ab8>]
(arch_cpu_idle+0x20/0x3c)
[    0.085549] [<c0210ab8>] (arch_cpu_idle) from [<c02647f0>]
(cpu_startup_entry+0x2c0/0x5dc)
[    0.085576] [<c02647f0>] (cpu_startup_entry) from [<c099bc1c>]
(start_kernel+0x358/0x3c4)
[    0.085600] [<c099bc1c>] (start_kernel) from [<8020807c>] (0x8020807c)


Let me know if there's any patches you'd like me to test, or if you'd
like config details.

thanks
-john
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