[PATCH 4.2.y-ckt 130/218] x86/apic: Fix suspicious RCU usage in smp_trace_call_function_interrupt()

From: Kamal Mostafa
Date: Thu Mar 31 2016 - 16:48:54 EST

4.2.8-ckt7 -stable review patch. If anyone has any objections, please let me know.


From: Dave Jones <davej@xxxxxxxxxxxxxxxxx>

commit 7834c10313fb823e538f2772be78edcdeed2e6e3 upstream.

Since 4.4, I've been able to trigger this occasionally:

[ INFO: suspicious RCU usage. ]
4.5.0-rc7-think+ #3 Not tainted
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/20160315012054.GA17765@xxxxxxxxxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

./arch/x86/include/asm/msr-trace.h:47 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 = 1
RCU used illegally from extended quiescent state!
no locks held by swapper/3/0.

stack backtrace:
CPU: 3 PID: 0 Comm: swapper/3 Not tainted 4.5.0-rc7-think+ #3
ffffffff92f821e0 1f3e5c340597d7fc ffff880468e07f10 ffffffff92560c2a
ffff880462145280 0000000000000001 ffff880468e07f40 ffffffff921376a6
ffffffff93665ea0 0000cc7c876d28da 0000000000000005 ffffffff9383dd60
Call Trace:
<IRQ> [<ffffffff92560c2a>] dump_stack+0x67/0x9d
[<ffffffff921376a6>] lockdep_rcu_suspicious+0xe6/0x100
[<ffffffff925ae7a7>] do_trace_write_msr+0x127/0x1a0
[<ffffffff92061c83>] native_apic_msr_eoi_write+0x23/0x30
[<ffffffff92054408>] smp_trace_call_function_interrupt+0x38/0x360
[<ffffffff92d1ca60>] trace_call_function_interrupt+0x90/0xa0
<EOI> [<ffffffff92ac5124>] ? cpuidle_enter_state+0x1b4/0x520

Move the entering_irq() call before ack_APIC_irq(), because entering_irq()
tells the RCU susbstems to end the extended quiescent state, so that the
following trace call in ack_APIC_irq() works correctly.

Suggested-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Fixes: 4787c368a9bc "x86/tracing: Add irq_enter/exit() in smp_trace_reschedule_interrupt()"
Signed-off-by: Dave Jones <davej@xxxxxxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
arch/x86/include/asm/apic.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
index c839363..fa2f39f 100644
--- a/arch/x86/include/asm/apic.h
+++ b/arch/x86/include/asm/apic.h
@@ -640,8 +640,8 @@ static inline void entering_irq(void)

static inline void entering_ack_irq(void)
- ack_APIC_irq();
+ ack_APIC_irq();

static inline void ipi_entering_ack_irq(void)