linux-kernel - [PATCH] percpu: use notrace variant of preempt_disable/preempt

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Message-Id: <20161103135838.GB9487@osiris>
Date:   Thu, 3 Nov 2016 14:58:38 +0100
From:   Heiko Carstens <heiko.carstens@...ibm.com>
To:     Tejun Heo <tj@...nel.org>, Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org,
        Sebastian Ott <sebott@...ux.vnet.ibm.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: [PATCH] percpu: use notrace variant of preempt_disable/preempt_enable

Commit 345ddcc882d8 ("ftrace: Have set_ftrace_pid use the bitmap like
events do") added a couple of this_cpu_read calls to the ftrace code.

On x86 this is not a problem, since it has single instructions to read
percpu data. Other architectures which use the generic variant now
have additional preempt_disable and preempt_enable calls in the core
ftrace code. This may lead to recursive calls and in result to a dead
machine, e.g. if preemption and debugging options are enabled.

To fix this use the notrace variant of preempt_disable and
preempt_enable within the generic percpu code.

Reported-and-bisected-by: Sebastian Ott <sebott@...ux.vnet.ibm.com>
Tested-by: Sebastian Ott <sebott@...ux.vnet.ibm.com>
Fixes: 345ddcc882d8 ("ftrace: Have set_ftrace_pid use the bitmap like events do")
Signed-off-by: Heiko Carstens <heiko.carstens@...ibm.com>
---
 include/asm-generic/percpu.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/asm-generic/percpu.h b/include/asm-generic/percpu.h
index 40e887068da2..0504ef8f3aa3 100644
--- a/include/asm-generic/percpu.h
+++ b/include/asm-generic/percpu.h
@@ -118,9 +118,9 @@ do {									\
 #define this_cpu_generic_read(pcp)					\
 ({									\
 	typeof(pcp) __ret;						\
-	preempt_disable();						\
+	preempt_disable_notrace();					\
 	__ret = raw_cpu_generic_read(pcp);				\
-	preempt_enable();						\
+	preempt_enable_notrace();					\
 	__ret;								\
 })

-- 
2.8.4