On 03/23/2016 01:24 PM, Steven Rostedt wrote:
From: "Steven Rostedt (Red Hat)" <rostedt@xxxxxxxxxxx> 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@xxxxxxx> Fixes: 07d777fe8c398 "tracing: Add percpu buffers for trace_printk()" Cc: stable@xxxxxxxxxxxxxxx # v3.5+ Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Tested-by: Vlastimil Babka <vbabka@xxxxxxx> Thanks! -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html