81 lines
3.1 KiB
Diff
81 lines
3.1 KiB
Diff
|
From 28fb06421ab3d9256d32611138306470996cc4c1 Mon Sep 17 00:00:00 2001
|
||
|
|
From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>
|
||
|
|
Date: Tue, 22 Mar 2016 17:30:58 -0400
|
||
|
|
Subject: [PATCH] UPSTREAM: tracing: Fix trace_printk() to print when not using
|
||
|
|
bprintk()
|
||
|
|
|
||
|
|
The trace_printk() code will allocate extra buffers if the compile detects
|
||
|
|
that a trace_printk() is used. To do this, the format of the trace_printk()
|
||
|
|
is saved to the __trace_printk_fmt section, and if that section is bigger
|
||
|
|
than zero, the buffers are allocated (along with a message that this has
|
||
|
|
happened).
|
||
|
|
|
||
|
|
If trace_printk() uses a format that is not a constant, and thus something
|
||
|
|
not guaranteed to be around when the print happens, the compiler optimizes
|
||
|
|
the fmt out, as it is not used, and the __trace_printk_fmt section is not
|
||
|
|
filled. This means the kernel will not allocate the special buffers needed
|
||
|
|
for the trace_printk() and the trace_printk() will not write anything to the
|
||
|
|
tracing buffer.
|
||
|
|
|
||
|
|
Adding a "__used" to the variable in the __trace_printk_fmt section will
|
||
|
|
keep it around, even though it is set to NULL. This will keep the string
|
||
|
|
from being printed in the debugfs/tracing/printk_formats section as it is
|
||
|
|
not needed.
|
||
|
|
|
||
|
|
Reported-by: Vlastimil Babka <vbabka@suse.cz>
|
||
|
|
Fixes: 07d777fe8c398 "tracing: Add percpu buffers for trace_printk()"
|
||
|
|
Cc: stable@vger.kernel.org # v3.5+
|
||
|
|
Bug: 34277115
|
||
|
|
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
|
||
|
|
Change-Id: I10ce56caa41c7644d9d290d9ed272a6d156c938c
|
||
|
|
---
|
||
|
|
include/linux/kernel.h | 6 +++---
|
||
|
|
kernel/trace/trace_printk.c | 3 +++
|
||
|
|
2 files changed, 6 insertions(+), 3 deletions(-)
|
||
|
|
|
||
|
|
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
|
||
|
|
index 44d0a02224897..0d1fa1b442209 100644
|
||
|
|
--- a/include/linux/kernel.h
|
||
|
|
+++ b/include/linux/kernel.h
|
||
|
|
@@ -554,7 +554,7 @@ do { \
|
||
|
|
|
||
|
|
#define do_trace_printk(fmt, args...) \
|
||
|
|
do { \
|
||
|
|
- static const char *trace_printk_fmt \
|
||
|
|
+ static const char *trace_printk_fmt __used \
|
||
|
|
__attribute__((section("__trace_printk_fmt"))) = \
|
||
|
|
__builtin_constant_p(fmt) ? fmt : NULL; \
|
||
|
|
\
|
||
|
|
@@ -601,7 +601,7 @@ extern int __trace_puts(unsigned long ip, const char *str, int size);
|
||
|
|
*/
|
||
|
|
|
||
|
|
#define trace_puts(str) ({ \
|
||
|
|
- static const char *trace_printk_fmt \
|
||
|
|
+ static const char *trace_printk_fmt __used \
|
||
|
|
__attribute__((section("__trace_printk_fmt"))) = \
|
||
|
|
__builtin_constant_p(str) ? str : NULL; \
|
||
|
|
\
|
||
|
|
@@ -621,7 +621,7 @@ extern void trace_dump_stack(int skip);
|
||
|
|
#define ftrace_vprintk(fmt, vargs) \
|
||
|
|
do { \
|
||
|
|
if (__builtin_constant_p(fmt)) { \
|
||
|
|
- static const char *trace_printk_fmt \
|
||
|
|
+ static const char *trace_printk_fmt __used \
|
||
|
|
__attribute__((section("__trace_printk_fmt"))) = \
|
||
|
|
__builtin_constant_p(fmt) ? fmt : NULL; \
|
||
|
|
\
|
||
|
|
diff --git a/kernel/trace/trace_printk.c b/kernel/trace/trace_printk.c
|
||
|
|
index a9077c1b4ad3f..fdb23e84b011b 100644
|
||
|
|
--- a/kernel/trace/trace_printk.c
|
||
|
|
+++ b/kernel/trace/trace_printk.c
|
||
|
|
@@ -272,6 +272,9 @@ static int t_show(struct seq_file *m, void *v)
|
||
|
|
const char *str = *fmt;
|
||
|
|
int i;
|
||
|
|
|
||
|
|
+ if (!*fmt)
|
||
|
|
+ return 0;
|
||
|
|
+
|
||
|
|
seq_printf(m, "0x%lx : \"", *(unsigned long *)fmt);
|
||
|
|
|
||
|
|
/*
|