linux-kernel - [PATCH] arm64: use preempt_disable_notrace in _percpu

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Message-Id: <1473338719-18647-1-git-send-email-zhang.chunyan@linaro.org>
Date:   Thu,  8 Sep 2016 20:45:19 +0800
From:   Chunyan Zhang <zhang.chunyan@...aro.org>
To:     rostedt@...dmis.org, mingo@...hat.com
Cc:     zhang.lyra@...il.com, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.orgi, takahiro.akashi@...aro.org,
        mark.yang@...eadtrum.com
Subject: [PATCH] arm64: use preempt_disable_notrace in _percpu_read/write

When debug preempt or preempt tracer is enabled, preempt_count_add/sub()
can be traced by function and function graph tracing, and
preempt_disable/enable() would call preempt_count_add/sub(), so in Ftrace
subsystem we should use preempt_disable/enable_notrace instead.

In the commit 345ddcc882d8 ("ftrace: Have set_ftrace_pid use the bitmap
like events do") the function this_cpu_read() was added to
trace_graph_entry(), and if this_cpu_read() calls preempt_disable(), graph
tracer will go into a recursive loop, even if the tracing_on is
disabled.

So this patch change to use preempt_enable/disable_notrace instead in
this_cpu_read().

Since Yonghui Yang helped a lot to find the root cause of this problem,
so also add his SOB.

Signed-off-by: Yonghui Yang <mark.yang@...eadtrum.com>
Signed-off-by: Chunyan Zhang <zhang.chunyan@...aro.org>
---
 arch/arm64/include/asm/percpu.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/percpu.h b/arch/arm64/include/asm/percpu.h
index 0a456be..2fee2f5 100644
--- a/arch/arm64/include/asm/percpu.h
+++ b/arch/arm64/include/asm/percpu.h
@@ -199,19 +199,19 @@ static inline unsigned long __percpu_xchg(void *ptr, unsigned long val,
 #define _percpu_read(pcp)						\
 ({									\
 	typeof(pcp) __retval;						\
-	preempt_disable();						\
+	preempt_disable_notrace();					\
 	__retval = (typeof(pcp))__percpu_read(raw_cpu_ptr(&(pcp)), 	\
 					      sizeof(pcp));		\
-	preempt_enable();						\
+	preempt_enable_notrace();					\
 	__retval;							\
 })

 #define _percpu_write(pcp, val)						\
 do {									\
-	preempt_disable();						\
+	preempt_disable_notrace();					\
 	__percpu_write(raw_cpu_ptr(&(pcp)), (unsigned long)(val), 	\
 				sizeof(pcp));				\
-	preempt_enable();						\
+	preempt_enable_notrace();					\
 } while(0)								\

 #define _pcp_protect(operation, pcp, val)			\
-- 
2.7.4