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| author | Steven Rostedt (Red Hat) <rostedt@goodmis.org> | 2016-03-22 17:30:58 -0400 |
|---|---|---|
| committer | Sasha Levin <sasha.levin@oracle.com> | 2016-04-18 08:51:06 -0400 |
| commit | bef794e8c891b60da2dec86c90f1e46fa142ea1e (patch) | |
| tree | a9e8b8eb99829123676c84ce406f53ec33225db7 | |
| parent | 01954dfd48d936199204ae0860897b8aed18c1e2 (diff) | |
| download | lwn-bef794e8c891b60da2dec86c90f1e46fa142ea1e.tar.gz lwn-bef794e8c891b60da2dec86c90f1e46fa142ea1e.zip | |
tracing: Fix trace_printk() to print when not using bprintk()
[ Upstream commit 3debb0a9ddb16526de8b456491b7db60114f7b5e ]
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+
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
| -rw-r--r-- | include/linux/kernel.h | 6 | ||||
| -rw-r--r-- | 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 3a5b48e52a9e..d837f2a41665 100644 --- a/include/linux/kernel.h +++ b/include/linux/kernel.h @@ -606,7 +606,7 @@ 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; \ \ @@ -650,7 +650,7 @@ int __trace_printk(unsigned long ip, const char *fmt, ...); */ #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; \ \ @@ -672,7 +672,7 @@ 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 36c1455b7567..6d6c0411cbe8 100644 --- a/kernel/trace/trace_printk.c +++ b/kernel/trace/trace_printk.c @@ -289,6 +289,9 @@ 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); /* |