linux-kernel - [PATCH 3.19.y-ckt 103/170] x86/apic: Fix suspicious RCU usage in smp_trace_call_function

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Message-Id: <1459558456-24452-104-git-send-email-kamal@canonical.com>
Date:	Fri,  1 Apr 2016 17:53:09 -0700
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Andi Kleen <ak@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Dave Jones <davej@...emonkey.org.uk>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 3.19.y-ckt 103/170] x86/apic: Fix suspicious RCU usage in smp_trace_call_function_interrupt()

3.19.8-ckt18 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Dave Jones <davej@...emonkey.org.uk>

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@...ux.intel.com>
Link: http://lkml.kernel.org/r/20160315012054.GA17765@codemonkey.org.uk
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

-------------------------------
./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@...ux.intel.com>
Fixes: 4787c368a9bc "x86/tracing: Add irq_enter/exit() in smp_trace_reschedule_interrupt()"
Signed-off-by: Dave Jones <davej@...emonkey.org.uk>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 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 465b309..dbaf844 100644
--- a/arch/x86/include/asm/apic.h
+++ b/arch/x86/include/asm/apic.h
@@ -651,8 +651,8 @@ static inline void entering_irq(void)
 
 static inline void entering_ack_irq(void)
 {
-	ack_APIC_irq();
 	entering_irq();
+	ack_APIC_irq();
 }
 
 static inline void exiting_irq(void)
-- 
2.7.4