Commit-ID: 9311a4c9f0d2d5404cd7bc2ba913c919418f83e2
Gitweb: http://git.kernel.org/tip/9311a4c9f0d2d5404cd7bc2ba913c919418f83e2
Author: Steven Rostedt <rostedt@xxxxxxxxxxx>
AuthorDate: Thu, 8 Sep 2016 12:34:33 -0400
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 6 Oct 2016 09:55:07 +0200
locking/lockdep: Quiet GCC about dangerous __builtin_return_address() operations
GCC's new warnings about __builtin_return_address(n) operations with
n > 0 is popping up around the kernel. The operation is dangerous, and
the warning is "good to know". But there's instances that we use
__builtin_return_address(n) with n > 0 and are aware of the issues,
and work around them. And its used mostly for tracing and debugging. In
these cases, the warning becomes a distraction and is not helpful.
To get better lock issue traces, a function like get_lock_parent_ip()
uses __builtin_return_address() to find the caller of the lock, and
skip over the internal callers of the lock itself. Currently it is only
used in the kernel/ directory and only if certain configs are enabled.
Create a new config called CONFIG_USING_GET_LOCK_PARENT_IP that gets
selected when another config relies on get_lock_parent_ip(), and this
will now enable the function get_lock_parent_ip(), otherwise it wont be
defined. It will also disable the frame-address warnings from GCC in
the kernel directory.
Reported-and-tested-by: Borislav Petkov <bp@xxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Acked-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/20160908123433.2cf93b96@xxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
include/linux/ftrace.h | 2 ++
kernel/Makefile | 7 +++++++
kernel/trace/Kconfig | 1 +
lib/Kconfig.debug | 10 ++++++++++
4 files changed, 20 insertions(+)
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 6f93ac4..1218b15 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -714,6 +714,7 @@ static inline void __ftrace_enabled_restore(int enabled)
#define CALLER_ADDR5 ((unsigned long)ftrace_return_address(5))
#define CALLER_ADDR6 ((unsigned long)ftrace_return_address(6))
+#ifdef CONFIG_USING_GET_LOCK_PARENT_IP
static inline unsigned long get_lock_parent_ip(void)
{
unsigned long addr = CALLER_ADDR0;
@@ -725,6 +726,7 @@ static inline unsigned long get_lock_parent_ip(void)
return addr;
return CALLER_ADDR2;
}
+#endif
#ifdef CONFIG_IRQSOFF_TRACER
extern void time_hardirqs_on(unsigned long a0, unsigned long a1);
diff --git a/kernel/Makefile b/kernel/Makefile
index e2ec54e..bff8214 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -11,6 +11,13 @@ obj-y = fork.o exec_domain.o panic.o \
notifier.o ksysfs.o cred.o reboot.o \
async.o range.o smpboot.o
+# Tracing may do some dangerous __builtin_return_address() operations
+# We know they are dangerous, we don't need gcc telling us that.
+ifdef CONFIG_USING_GET_LOCK_PARENT_IP
+FRAME_CFLAGS := $(call cc-disable-warning,frame-address)
+KBUILD_CFLAGS += $(FRAME_CFLAGS)
+endif
+
obj-$(CONFIG_MULTIUSER) += groups.o
ifdef CONFIG_FUNCTION_TRACER
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index ba33267..ecc0bbc 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -192,6 +192,7 @@ config PREEMPT_TRACER
select RING_BUFFER_ALLOW_SWAP
select TRACER_SNAPSHOT
select TRACER_SNAPSHOT_PER_CPU_SWAP
+ select USING_GET_LOCK_PARENT_IP
help
This option measures the time spent in preemption-off critical
sections, with microsecond accuracy.
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index cab7405..dbc49c4 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -977,6 +977,7 @@ config TIMER_STATS
config DEBUG_PREEMPT
bool "Debug preemptible kernel"
depends on DEBUG_KERNEL && PREEMPT && TRACE_IRQFLAGS_SUPPORT
+ select USING_GET_LOCK_PARENT_IP
default y
help
If you say Y here then the kernel will use a debug variant of the
@@ -1159,8 +1160,17 @@ config LOCK_TORTURE_TEST
endmenu # lock debugging
+config USING_GET_LOCK_PARENT_IP
+ bool
+ help
+ Enables the use of the function get_lock_parent_ip() that
+ will use __builtin_return_address(n) with n > 0 causing
+ some gcc warnings. When this is selected, those warnings
+ will be suppressed.
+
config TRACE_IRQFLAGS
bool
+ select USING_GET_LOCK_PARENT_IP
help
Enables hooks to interrupt enabling and disabling for
either tracing or lock debugging.
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