path: root/kernel
diff options
authorSteven Rostedt (Red Hat) <rostedt@goodmis.org>2016-03-22 17:30:58 -0400
committerSasha Levin <sasha.levin@oracle.com>2016-04-18 08:49:38 -0400
commit51d109b05dea76910c6b5c95908e9e334888f46f (patch)
treeae2c325cf72e8134319757cb376707b26fa8c3c7 /kernel
parent241a9a816bc95d7bbc7c422c60e880491a59ac1b (diff)
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>
Diffstat (limited to 'kernel')
1 files changed, 3 insertions, 0 deletions
diff --git a/kernel/trace/trace_printk.c b/kernel/trace/trace_printk.c
index 2900817ba65c..14ffaa59a9e9 100644
--- a/kernel/trace/trace_printk.c
+++ b/kernel/trace/trace_printk.c
@@ -291,6 +291,9 @@ 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);