[PATCH v2] x86/apic: Fix suspicious RCU usage

[Wanpeng Li]

From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>

===============================
[ INFO: suspicious RCU usage. ]
4.8.0-rc6+ #5 Not tainted
-------------------------------
./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 = 0
RCU used illegally from extended quiescent state!
no locks held by swapper/2/0.

stack backtrace:
CPU: 2 PID: 0 Comm: swapper/2 Not tainted 4.8.0-rc6+ #5
Hardware name: Dell Inc. OptiPlex 7020/0F5C5X, BIOS A03 01/08/2015
 0000000000000000 ffff8d1bd6003f10 ffffffff94446949 ffff8d1bd4a68000
 0000000000000001 ffff8d1bd6003f40 ffffffff940e9247 ffff8d1bbdfcf3d0
 000000000000080b 0000000000000000 0000000000000000 ffff8d1bd6003f70
Call Trace:
 <IRQ>  [<ffffffff94446949>] dump_stack+0x99/0xd0
 [<ffffffff940e9247>] lockdep_rcu_suspicious+0xe7/0x120
 [<ffffffff9448e0d5>] do_trace_write_msr+0x135/0x140
 [<ffffffff9406e750>] native_write_msr+0x20/0x30
 [<ffffffff9406503d>] native_apic_msr_eoi_write+0x1d/0x30
 [<ffffffff9405b17e>] smp_trace_call_function_interrupt+0x1e/0x270
 [<ffffffff948cb1d6>] trace_call_function_interrupt+0x96/0xa0
 <EOI>  [<ffffffff947200f4>] ? cpuidle_enter_state+0xe4/0x360
 [<ffffffff947200df>] ? cpuidle_enter_state+0xcf/0x360
 [<ffffffff947203a7>] cpuidle_enter+0x17/0x20
 [<ffffffff940df008>] cpu_startup_entry+0x338/0x4d0
 [<ffffffff9405bfc4>] start_secondary+0x154/0x180

This can be reproduced readily by running ftrace test case of kselftest.

Move the irq_enter() call before ack_APIC_irq(), because irq_enter()
tells the RCU susbstems to end the extended quiescent state, so that the
following trace call in ack_APIC_irq() works correctly, the same for 
exiting_ack_irq();
 
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
---
v1 -> v2:
 * add the same fix for exiting_ack_irq().

 arch/x86/include/asm/apic.h | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
index 1243577..f5aaf6c 100644
--- a/arch/x86/include/asm/apic.h
+++ b/arch/x86/include/asm/apic.h
@@ -650,8 +650,8 @@ static inline void entering_ack_irq(void)
 
 static inline void ipi_entering_ack_irq(void)
 {
-	ack_APIC_irq();
 	irq_enter();
+	ack_APIC_irq();
 }
 
 static inline void exiting_irq(void)
@@ -661,9 +661,8 @@ static inline void exiting_irq(void)
 
 static inline void exiting_ack_irq(void)
 {
-	irq_exit();
-	/* Ack only at the end to avoid potential reentry */
 	ack_APIC_irq();
+	irq_exit();
 }
 
 extern void ioapic_zap_locks(void);
-- 
1.9.1